Why do faster than light signals break spacetime?
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- Опубліковано 27 вер 2024
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Let's explore why faster than light signals reverse time and break causality. Why they can make effects occur before cause, causing time paradoxes.
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first
Sir,unable to get 30 days free trail even after clicking the link.
Space time diagrames use 45° angle for light only as CONVENTION. If you decide angle for light is 0°, light particles would not travel back in time but travel in present and wouldn't experience time. Misconception of this video is it suggests faster than light particles would travel back in time. Retarded action is the reason why physics cannot make progress, since relativity suggests every particle travelling faster than light travel into the past. But the truth is faster than light particles travel into the present from the perspective of the source, they don't actually travel back in time. Relativity of simultaneity opens a possibility for faster than light propagation, since synchronization convention prevents you from measuring one way speed of light.
@TriTr-qd2bd If there was no speed of light, universe would look the same but eveything would happen all at once. Speed of light is actually speed of causality, which suggest c is round trip distance divided by time.
nah. this episode was way too forced. in real life faster than light travel dont cause time travel.. it just shortens time and the people you used in the example dont know about FTL and cant do proper calculations.
If you don't understand the shirt in calculus if we consider x to be position and t to be time then the rate of change of the position over time is called dx/dt. The rate of change of velocity is acceleration and so it's d^2x/dt^2. The rate of change of acceleration is d^3x/dt^3 and the name for that is jerk. So the shirt says "Don't be a jerk".
And bonus fun fact for cereal fans: the 4th, 5th and 6th derivatives are called snap, crackle and pop.
Thanks
bro i legit came here to explain the same thing but u beat me to it. kudos!
Thanku I'm always curious about his shirts what they mean sometimes when I didn't get it and someone explain it in the comment section it's always heaven to my heart 💝 😊😌😌😌
"What will it be?" bartender asks. Tachyon walks into a bar.
Causality has left the room
@Mahesh_Shenoy bomb moves backwards from bomb or the event occurs chronologically in reverse?
What’s the difference between the two?
Entropy
Well not really, just seems like it to the near speed of light observer
Relativity is seriously a amazing topic to talk to the people's who likes it
Yeah, its great if you have friends that share same intrest
it is interesting their finding that, technically its possible to look back in time. but the idea is nothing like back to the future movie or anything... i mean deterioration of the universe, rotting, aging, ( whatever you call it.. ) - could go slightly backwards just walking around. but in our eyes this would be like 1 in 1000th of a second, i mean you wouldnt even notice it. you couldnt even do the dejavu cat from the matrix. and its a 1 in billion possibility in every day life...
Our observation of reality, and reality aren't the same thing. Models need to remember that perception and reality are not the same thing.
@@chrisoakey9841 objective reality don't exist tough, atleast we can't see.
@@malemsana_only we cant see, but in general dont need to as the stuff that affects us enough to make a difference are seeable. we dont worry about the pull of gravity from proxima because it is insignificant. but models like general relativity are fine until we extrapolate concepts like space compression etc because of taking the model of our observation and suggesting that we therefore know... which results in idiotic things like the expanding universe, dark matter and dark energy and twin paradoxes etc.
I wish you SHOWED us at 22:14 how causality is broken when the fast observer send FTL message to stop the bomb. That was the most important part of the entire visualization of events
Missed that too
Yup simply observation will not do anything
Even if he had some instantaneous transmission device, his trigger would be the reception of the light signal. This, by nature, would have taken a year (relative to the ship) so the signal would arrive at the exact moment the launch signal arrived at the second ship. Still not breaking causality.
The blue ships trigger is the explosion. The blue ship is right next to explosion when it happens, so the time it takes for the light signal of the explosion to reach the blue ship is negligible. If they send an instant/ftl/faster than missile signal to the destroyer, that’s the paradox. Rewatch starting at 20:00, with key points at 22:00
@@nickwalden6425 It would seem so, but it isn't, is it. No matter when you send the signal and how fast you send it, the missile was already fired from the firing ship's perspective and the moon has already been blown up by the missile before any signal reaches the blue ship.
Here's my idea of what actually happens:
Ship a fires an FTL missile, the missile blows up the moon, ship b sees the moon blown up, ship b sends an FTL signal to ship a, ship a can receive this signal anywhen between the moment that the explosion was seen by ship b and infinite time from now in the future, depending on which direction and speed ship a has in relation to ship b's message signal.
From ship b's perspective their message will reach ship a in the future, after they see the moon explode and the ship firing the missile, and not in the past. The light from ship a at the time when it receives the missile will reach ship b waaaaaaaay after it has all happened.
There is no breach of causality. It's only that some observers will not be able to calculate the correct order of events without additional maths that corrects for the incorrectly observed time that passes for each event from their perspective. Some events, like the path the missile traverses, will seem to go backwards, but in reality they don't, they just go really really fast.
To actually break causality you'd have to find a way to send the signal to a time before the missile was fired and that didn't happen, and wouldn't, no matter the speed. Even at infinite speed you'd still be stuck with the present. We have to remember that we can see the past because light takes time to get here. Things in the past have already happened, regardless of the time or speed with which our information is updated with the events.
How is the causality broken in any of the cases discussed? As you said, what you see is not what is happening. So, even if the explosion is observed to happen before the missile is being launched. In reality, the effect is still following the cause. For example, we see lightning before the thunder. But anyhow the thunder occurred before the lightning. So, even if we are seeing the causality to break just because of seeing light signals in wrong order, that does not mean that the events have also occurred in wrong order. So the causality should not be broken even if the missile is travelling faster than light. Consequently, the argument that causality will break if an object travels faster than light should not stand. As an analogy, a supersonic aircraft travels faster than the speed of sound resulting in different effects without breaking the causality.
You explain well, in a very simple and entertaining way. Thank you, for sharing. Keep educating us.
The lighting example dont work because one event is not causing the other. The sound and the light comes from the same event, but is not one that is leading to the other.
And examples using sound waves also dont work because sound uses air as a medium. Most experients bases itself in a vacuum. But sound not travel in a vacuum.
@life-my9tl I was wondering the same thing! I wrote a comment wondering if you redid the thought experiment, but with a supersonic missile and observers LISTENING for these events, would the causality also be broken? And @sonofcronos7831 I think it’s ok to just add air to the thought experiment so that sound can propagate, or assume sound is also an EM wave for the sake of thought experiment
It's not a real explanation, but I think a good way to think about it is like this: You are always constantly travelling at the speed of light. But that speed is distributed between time and space. The faster you move through space, the slower you move through time and vice versa. But no matter what the distribution is, both speeds must sum to lightspeed. If you then want to travel through space faster than light, while the sum stays fixed, you have to have a negative speed through time.
In the spaceship’s frame, the explosion did happen before launching the FTL missile. Check that section of the video again :)
Supersonic travel doesn’t contract space, so it’s not an appropriate analogy. This weird concept is happening because traveling at the speed of light is doing a weird effect on spacetime. Any other speed can’t be used as an analogy
i have to admit your are really smooth with the promos
Haha, thanks!
@@Mahesh_Shenoy breaking of causality is not a paradox but an usual phenomenon.rocket's light will travel slower than rocket therefore we will see that rocket hasn't hit anything but in reality rocket would already have smashed into the object and the light of the moment when rocket hit the object will take time to reach us therefore we will see destroyed object first then we will see rocket smashing into object.
@@pwinsider007 What you've described was the first scenario, with the astronaut right next to the planet - there's an illusion that makes it look like it happened in reverse, but it actually didn't. The second scenario, with the near-light-speed space ship passing the planet at the time of impact shows that for some observers, the events *actually* happen in reverse, it's not just an illusion that makes it look that way.
Hands down the best relativity physics content on UA-cam. Your approach of leading the audience to discover the meaning of each concept for themselves with the help of animations and Socratic dialogue is wonderful. A superb teacher.
Before this video I didn't understand what the problem with seeing things backwards is, now thanks to the faster than light signal "don't shoot!" I understand. Bravo, as usual! Event circles is also a good depiction
I wanted to see how the faster than light "don't shoot" signal traveling, he said it will arrive before the light of the moment they "shot" the bomb, but how though? I wish he showed us instead of just saying it does
@@abdulqader1829 You can imagine it going arbitrarily quickly, or even instantly, after the "boom" detection as the animation plays.
Closed timelike loops
@@abdulqader1829On a regular 1D+1D Minkowski spacetime diagram, two inertial observers at physically distant locations in space, usually get drawn as parallel vertical lines... But... The "same time" for each of those observers are connected with 45° diagonal lines. (It's not a horizontal displacement on the graph.)
To shift from one observer's coordinate system to the other, you slide the parallel lines up and down (in time) so that points intersecting on the same 45° diagonal line, will be moved to match on the diagonal line perpendicular to the first one (i.e. -45° or 135°)
Faster than light signals will intersect with the "past" of each observer's vertical line after transforming to the other observer's coordinate system.
(This happens _both ways_ symmetrically.)
If the boom is the triggering event to send a signal to stop the boom, then it is irrelevant because by virtue of the boom happening, the firing had already happened.
Does sending a signal back to the destroyer to tell them to stop firing erases the boom from happening? Of course not.
Therefore, causality is maintained.
The missile knows when it is in all reference frames. It knows this because it knows when it isn’t.
Someone was a missileer
There's a couple things about this sort of thing I've found fascinating for a while now.
First is that if there was a stationary observer sitting somewhere between the destroyer and the moon, when the FTL missile passed them they would get the optical equivalent of a sonic boom. They would see the image of the missile appear out of nowhere at the point of its closest approach, then *split in two.* One image would race forwards towards the moon, the other backwards towards the destroyer. Like the astronaut they could do the math later and work out the order of events, but I still find it neat.
Second is that there's a relationship between the speeds of the spaceship and the FTL missile in order for causality to break. If the ship isn't traveling close enough to lightspeed, it won't see causality break. Similarly, if the missile isn't travel as far above lightspeed -- let's say, only two or three times lightspeed instead of four -- the spaceship won't see causality break. As demonstrated, at exactly the right combination of speeds the spaceship sees it all happen simultaneously.
I don't know the math well enough to figure this out exactly, but I have a hunch it's something close to an inverse relationship between the speed of the missile and the time dilation/length contraction observed by the spaceship. It's not the raw speed of the spaceship because the relativistic effects don't scale linearly; you don't get 50% time dilation/length contraction at 50% of lightspeed, you get it at about 86.6% of lightspeed.
So for a spaceship observing 10% time dilation/length contraction (41.7% lightspeed), you would only start to see causality break from things traveling more than ten times faster than light.
At 20% TD/LC (55% lightspeed) you'd see it break for things above five times faster.
At 50% TD/LC it would break for anything above two times lightspeed.
You can break causality with any signal velocity greater than light and a much clearer demonstration of this is to do a round-trip journey from "Location A" to "Location B" and then back to "Location A" again. If the trip is done faster than light [FTL] it will arrive at its destination "Location A" *_BEFORE_* it departed from "Location A". I was hoping that this video would demonstrate this case, but it didn't.
The math is a line, y = Mx + b, so you can do it. For a launch at t,X = 0,0 in years, light years, and an impact at (1/v, 1) where v is the missile speed. For a rocket ship going u and launch it 0,0. The hit occurs at t’ = gamma(1/v - u), so Lorentz contraction and time dilation are irrelevant, but the break point is indeed inverse u > c^2 / v
@@juliavixen176 it’s from pov of B. From pov A sequence is normal. You can’t see spacecraft coming at point b from pov b, but once it arrives, images of it’s travel will appear like moving backward, and then you’ll see launch from point A. And if before that spacecraft launches from B to A, from perspective of B, that didn’t see launching yet, it will seems like spacecraft will return before it was launched. But when light reaches B all sequences will be in order. From Pov B the’ll see two spacecrafts flight towards A. One of them moving backwards, and another moving forward. But they reach A with same delay as between arrival at B and departure. And as far as I understand, we don’t really understand what means (-dt)^(1/2) (result of v > c). Maybe it’s just limit of theory, or maybe time travel in some way. If it’s later, than causality can be broken, but it’s likely former.
It can be considered as time travel in a way. Imagine B observing caveman on A in far system, and suddenly those ”caveman” arrive to B on FTL spacecraft.
@vichav3167 Location A and Location B _are both in each other's past_ symmetrically. The FTL object/signal arrives in the past of the other location _each way_
A round trip puts the FTL thing in *everyone's past* including the original location where it started.
In Special Relativity, time *is* space. Every location in space is a location in time, and every location in space is in the past of every other location in space. (The use of " _i_ " on the time coordinate is a mathematical way to deal with this.) When you look with your eyes, in a straight line from the tip of your nose out into distant space, what you are currently seeing _right now_ is the past.
The straight line distance away from you in space is the 45° line on a Minkowski spacetime diagram. Everything you see and interact with *_right now_* is on this 4D light cone. Anything not on this light cone is not happening to you _right now_
That's time; time is the radial distance in a "straight line" away from you.
Velocity is just the conversion factor between two observers of how much of spacetime to label "space" and how much to label "time" for each other... because all inertial observers are at rest with respect to themselves and their clock always ticks at one second per second.
A simple way to rework this is to imagine the default refresh rate of the universe is C (Light speed) so if something could move faster than the speed of light it wouldn't be drawn properly . It might look something like a laterally, directionally stretched object that flashes in time/space cycles as it moves through large areas of space and if you were to cut out all the gaps when it wasn't visible it would seem to be moving at C , but when you add the dark gaps in it's illumination you can deduce how much faster than C it's going . If time stands still at the speed of light then moving closer and closer to C would be like reducing the frame-rate until it's approaching zero frames a second which would be invisible . A simple way to think of it is how cameras make wheels going a certain speed start to appear to turn backwards . If you had an infinately powerful camera and you wanted to reduces the movement of light to a completely still image when reduced back to 24 frames a second , the best you could ever acheive is smaller and smaller fractions of a frame , which is why it would take infinite power to acheive 1c . But if you could go from 0c to 1c without accelerating , then you should be able to go over C . But it's just possible that going C+ looks like a ghostly still image beaming in and out of space in such a flash you might not see it if was right infront of your computer screen . Anything visible would be reduced to the same laws as seeing something move at lightspeed because it would be visual abberations of C speed photons being disturbed by a partially drawn mass . Maybe it would look more like a streched out collection of flickering entangled point particles . Maybe faster than light travel has an embedded quantum probability mechanic . Not really something I've given a lot of thought . Fun to imagine though . Anyway , just because you see an effect before a cause doesn't mean it actually happened that way . Could be little difference between that and using different speed communication devices to hear an answer before a question - it doesn't mean you have the ability from your perspective to get an answer before asking a question .
That's How I think about, and that also, maybe things move at discrete steps (yet really small ones) like a Planck's length. Because of light speed is limited and a field can't transmit information to all particles simultaniously (even though, entanglement effects could happen between bunch of particles, that wouldn't change the overall perspective for a macroscopic observation, so we could ignore it, if things go at speeds lesser than C).
General relativity and quantum mechanics will never be combined until we realize that each individual observer is observing them both at different moments in time. Because causality has a speed limit (c) every point in space where one observes it from will be the closest to the present moment. When one looks out into the universe they see the past which is made of particles (GR). When one tries to look at smaller and smaller sizes and distances, they are actually looking closer and closer to the present moment (QM). The wave property of particles appears when we start trying to predict the future of that particle. It is a probability wave because the future is probabilistic. Wave function collapse is what we perceive as the present moment and is what divides the past from the future. GR is making measurements in the observed past and therefore, predictable. It can predict the future but only from information collected from the past. QM is attempting to make measurements of the unobserved future and therefore, unpredictable. Only once a particle interacts with the present moment does it become predictable. This is an observational interpretation of the mathematics we currently use based on the limited perspective we have with the experiments we choose to observe the universe with.
Ain't reading all that
Read all of it. Makes perfect sense. Thank you for writing it!
That would mean that we can predict the future of a particle if we look at it from far away, but that's not true as far as I know
your first point what it basically says is that whenever you look into your past lightcone, you see particles and when you try to derive a outcome of the future lightcone by observing the past lightcone, then particles behave like waves?
@@aster2790 celestial objects are far away and made of particles and we can predict their motion.
First Video I see and I'm mainly disappointed because you're not just a floating head explaining physics.
You missed a critical step. We MUST change the frame of reference back to the destroyer's frame of reference when the message not to shoot is received. When we do that, there is no paradox. In your example, the moving ship observes the order of events as its message arrived before the missile was fired, but the destroyer still doesn't get the message until after from their frame of reference.
Here's an analogy sonic experiment to demonstrate why.
We have a gun pointed at a target down range. The gun has a light sensor that will lock the gun when the sensor activates. The target has a laser aimed at the gun's light sensor and will activate when a bullet hits the target. With the precision of our setup, we'll have an observer safely positioned near the target, ready to witness the sequence of events.
1) The gun fires.
2) The observer hears the bullet hit the target (I know this because I've been in this scenario).
2a) The laser fires.
3) The laser hits the gun's light sensor and locks the gun.
4) The observer hears the gunshot *BANG!
Even though the observer sees the gun lock before hearing it fire, we know the gun fired before the bullet hit the target.
I know folks may say, "But this is sonic, not the speed of light. They're different." Yes, but apply the same logic to the ships. If we keep the destroyer's frame of reference, they will never receive the message not to fire before they fire. You can even use instantaneous communication, like hypothetical portals, and there is no way to create a paradox.
Sabine Hossenfelder stated that FTL doesn't actually result in backwards causation because the paradox is due to only solving for SR, not GR, and the paradox goes away in the case of the latter.
I have a suggestion for your next t-shirt: a graphic with three cartoon characters eating a puffed rice breakfast cereal, each character labeled d^4x/dt^4, d^5x/dt^5, and of course d^6x/dt^6
Took me a moment.
@@astrokevin92 glad someone did 😉
snap, crackle and pop .....xD
I love this idea that the cause signal remains contained within the effect signal even under transformation for signals less than or at the speed of light. That is a fantastic way to arrive at the relationship between reference frames without calling on any maths. I'm going to watch this a few times to really bed down this representation.
also watch some animations of Minkowski diagrams (where the expanding circle here is repented by the light cones' X....it never moves, while the (t, x) axises flip flop around, that is: all references frame agree the effect envelope is a sphere expanding at the speed of light.
Insane.... Your explanations are traveling FTSL... I feel the effects even before you start explaining...
the only problem i have with this is that to me it means therhetically we can still travel ftl. All we need to do is create a dilation contraction bubble.
if an object or signal travels faster than light whilst interacting with the universe, it breaks causality sequence of events.
but isn't it theoretically then possible, that if we can create a bubble that surrounds the missile, that pulls it out from time dilation and length contraction affects of the universe.
we could fire a missile. once it would hit ftl speed. it would disappear like travelling into a wormhole and then only reappear once it drops below light speed and hits the moon.
basically ftl travel is akin to teleporation, or similar to travelling through wormholes, or similar to how 5th dimensional objects come into out dimension and dissappear from our dimension.
from the ships perspective, all they would see would be a missile suddenly pop into existence and hit the moon. they won't know what happened until months later when they'd see a missile being fired and disappearing from existence. so they wouldn't be able to send a message to the cruiser to not fire the missile.
so causality would not be broken. and we could still have ftl travel.
all it would mean is that ftl travel involves a type of teleporation / 5th dimensional movement of going out of our 4 dimensions and then coming back in.
So that causality can never be broken through the time dilation length contraction of other observers.
The transformations on the cause and effect loop, the length contractions are being made according to special relativity, which assumes the speed of light to be the limit. So using special relativity to say that faster than light travel doesn't exist while using it on a case where faster than speed of light travel occurs doesn't make sense to me.
No. Is exactly because faster than light breaks casuality that we know that nothing can travel faster than light, because one of the laws of physics is the law of casuality.
There's a much better demonstration, that wasn't covered in this video, of taking a round-trip voyage faster than light and arriving at where you started *BEFORE* you left. I was hoping that this would be in the video.
Intuitively understood so easily by the end; marvelous, thank you!
I love the energy you have while explaining things!
22:10 Intuitively I'd say, the problem is _transitioning_ a signal between slower-than-light and faster-than-light speeds. As long as the stl-"world" and ftl-world stay cleanly separated, causality doesn't break. Goes with what I heard, that the problem is _crossing_ the speed of light, not if you are below or above.
I have to think about that.
However: Reeeealy great video! Me like 😁
I don’t know about shattering spacetime, but photons do exactly that every time. So if create a mind experiment, in which photon released from Point A which lead to destruction of Point B, then spacecraft must see it in reverse too.
It’s impossible to see “rocket” at speed of light approaching. But light reflected of rocket still should exist. I think, that light reflected from rocket while it’s travelling must be taken in consideration, and shown as separated circle expanding at speed of light. Or maybe it’s effect of sqrt(-dt).
It took me a minute to get the joke on your shirt. Very clever.
At first I thought the shirt was saying “don’t be an accelerationist” (a sentiment I agree with!) but acceleration is second order, not third, so I was confused and stopped thinking about it. When I saw your comment I thought about it again, and remembered that third order force (jolt) is sometimes called “jerk” thus “don’t be (a) jerk”. Very good indeed!
Next he needs a shirt with three characters eating breakfast cereal, each character labeled d^4x/dt^4, d^5x/dt^5, and of course d^6x/dt^6
@@jpe1 Jerk is better than jolt because when you jerk something around you're changing the acceleration but when you jolt something you're probably throwing lightning around.
@@abebuckingham8198 I don’t disagree. When I learned physics in high school (_many_ years ago) it was jolt, but it seems jerk is now the more common term. Like, back then, my dad would have said (describing my mom’s driving) “don’t jolt the transmission” but now I think the more common phrase would be “don’t jerk the car around”
I'm still just impressed the astronaut can see a tiny ship and missile a light year away.
When we are in the original scenario, we looked at the length contraction from the missile POV. However, when looking at the FTL missile, you completely skip that step. I understand that the length contraction would make the distance imaginary, but it still seems like an important part of why things break at FTL.
The demonstration was mind-bending until the very end when you explained the "venn diagrams" of casualty, combined with stretching and shrinking of space within a reference frame. Causality really is nature's ultimate master.
22:21 But the problem is that this reverse phenomenon is only seen in the spaceship's perspective, no? Even if he sends a signal back, in the perspective of the shooter, the rocket has already launched. It is because of the limit of light's speed that the rocket is only seen after the boom occured.
Even if I didn't understand, just by your reaction and joyfulness makes the video fun❤
I don’t think I explained this well!!
Ek hi to dil.hai mahesh bhai
Kitni baar jeetoge
Par yeh dil maange more…Ahaaa!
Amazing video sir ! each and every video is getting even better!
waiting for the next one !
It's a good video explaining how FTL can create the illusion of the violation of causality, but nothing in it shows that causality was actually violated.
i love how you make everything so understandable keep doing what others don't i love it!!
I only get so attracted to any discussion regarding relativity.
13:00 guys save you some time. This is absolutely correct!
Thank you! I've been waiting soo long to find video explaining this in simple way and since I found your channel I was hoping that one day you will touch this subject.
Big thanks!
You're an phenomenal teacher! Einstein would be proud of you.
Sir, when things travel faster than the speed of light, it's only the effect that is visible and cause is not visible or visibly delayed. But cause effect relationship is not broken . It's maintained. It's just that we see only the effect and not the cause. That's it.
Hi, I love your explanation !
But I have a problem to understand why we care about someone perceive something?
Light is a wave, so the sound is, so when a lightning strike it appends before we hear it, doesn't make a mater.
And the animation would be the same with someone shoot a missile faster than sound (mach4 for example), at a distance from the strike, and a plane moving near the speed of sound...
Because an observer perceive something earlier doesn't make a mater from traveling speeder than sound or light ?
How every observer observes some event does not change how an event happened. Using the faster than light weapons you mentioned, objectively, the missile would be launched, before the impact...regardless of how other observers perceived it.
What you just shown does not mean causality is broken, and thus it meaning faster than light is possible....
If, hypothetically the spaceship were to detect such an event, we can conclusively proof that faster than light travel is 100% possible.
The final example about a signal being sent back to the destroyer to tell them not to fire, from the destroyer's perspective....the signal should be received after they fire.
Reality is reality. Something causes, something happens. Just because one sees it differently doesn't makes impossible.
Even if the hypothetical weapons is an instantaneous weapons with zero travel time (infinity speed), the moment the weapon is launched, it already hit. Even if the observer spaceship is travelling at the speed of light at the target, and saw the boom, from their perspective, the boom happened, then the light of the launch arrives...so, whatever fancy reconstruction of the event from their perspective is irrelevant. The spaceship's signal to the destroyer would've been red shifted to heck.
Exactly... I've been arguing this here ad nauseum... good to see that there are at least a few people left here that can think logically!
Like several other commenters, I too feel that the example used in the video *_does not break causality._* Before we start, don't forget that everybody-including you, the astronaut on the moon, and the people in the spaceship-can and should be doing relativistic calculations to understand what's really happening. Not just from their own reference frames (RF), but from everybody else's as well. Your video was a bit misleading in this respect. The people on the spaceship assumed that what they saw was their entire reality-they didn't do any calculations to dig deeper. But that's wrong. Appearances are deceptive. If they did the calculations, they'd get the same results as everybody else.
The "stationary" astronaut and the "moving" spaceship both see the explosion first and the missile launch happen later. But you only showed the astronaut doing the calculations. She therefore realized that in her own RF-as well as the launcher's-the missile launched first, and the explosion happened later. The calculations also show that in the spaceship's RF, the order of events was reversed. Everybody-including the people on the spaceship-can do the calculations. Everybody will get the same results. You yourself have emphasized the *Relativity of Simultaneity* several times in the past. Thanks to you, we already know that time behaves unintuitively in moving RFs. So why is it a contradiction this time?
As for the "moving" spaceship sending an FTL signal to the "stationary" missile launcher asking them not to launch the missile-here's the big reveal that you skipped: *From the missile launcher's RF, the FTL signal NEVER REACHES THEM!"* So again, no causality was broken.
Do the math: The spaceship is moving away from the launcher at v < c, say, 0.9c. It fires an FTL signal towards the launcher at |u'| > c, say 2c. So u' = -2c, the negative sign indicating that its direction is opposite to v. The signal approaches the launcher with a speed u = (v + u')/(1 + vu'/c²) = +1.375c. The positive sign means that the FTL signal is *moving away* from the missile launcher. (It actually doesn't matter if you take u' = +2c. u is still positive: +1.036c.)
So yeah, since the equations of Special Relativity are based on the assumption that nothing can travel FTL, you'll have to come up with new equations to explain how FTL signals behave. Only then will we be able to meaningfully discuss causality breaking. It's meaningless to use SR equations for FTL phenomena.
I'm thinking though, for the FTL missile: even if we see the missile's explosion's first and then the missile going backwards to the ship, if we knew the missile was FTL... can we incorporate that knowledge into our thinking and deduce that we saw the events in reverse?
I was thinking the same thing. Shouldn't the spaceship people have accounted for the fact they were themselves travelling in the same direction at relativistic speeds when they back-calculated where the missile came from? Wouldn't that account for the disparity in their view of cause and effect events?
I was left with the impression that there was a missing coordinate frame transformation there.
There's a much better demonstration, that wasn't covered in this video, of taking a round-trip voyage faster than light and arriving at where you started *BEFORE* you left. I was hoping that this would be in the video.
@@akaHarvesteR They did. What they "see" is different than what they calculated, and they still reached the conclusion that it happened backwards. The only way for them to conclude that the cause happened first would be to assume they are not valid observers, or that the astronaut POV is more valid (remember, from their perspective she is the one traveling backwards at relativistic speeds). That also goes against relativity, because all inertial observers are valid regardless of velocity (and they all observe the speed of light to be the same).
See the astronaut, she also saw the explosion first, but she could calculate it backwards and realize that the missile is FTL and was launched before the explosion without assuming she isn't a valid observer. The ship did the same and reached a different conclusion.
You could do the same experiment with the destroyer and the target both traveling close to the speed of light and the ship being "stationary". They would still find that the explosion happened first (the target would still see it happening first but conclude it happened afterwards).
EDIT: Just to be clear, the ship will be able to conclude that the missile was shot first from the reference frame of the destroyer or the astronaut. But since they are also a valid reference frame, you can't just do that and call the other reference frame "more correct". There is nothing that makes the ship a less valid reference frame.
Reminds me of videos where the distance is far enough, and a bullet is fired and travels faster than the speed of sound towards you, and you hear the bullet hit a target close by, then the sound of the gun firing is heard. Cody's Lab did a video on that.
Not sure how you could be traveling at the speed of sound past the target and still hear it get hit; that might be non-trivial.
I love how the titles of these are stated as matters of fact. 😅
Why? Are saying it’s not fact?
at 11:50 from the spaceship perspective the missile launcher was traveling left(let in negative direction) then the missile has to first overcome that negative velocity(due to inertia) to hit the moon and this will slower it and finally take 1 light year only.Can anyone please answer this question.
From the spaceship's perspective launcher was traveling in negative direction but, so does the moon. It means moon is also moving in the same negative direction at same speed which means missile would need equivalently less time to travel to the moon.
So, one of the big things not mentioned in this video is that the spaceship who launched (will launch) the missile, watched it flying backwards towards them for several months after the moon went "boom". When the backwards missile finally reached them, _they launch it_
Seriously, faster than light stuff travels backwards in time.
No, it still takes 1 year to travel boom effect to the one who launched and he will still see normal, not backwards because the closer images of missile reach him first.
@@wargod1722 Think about it: when do they see the light from the missile, and where is the missile. The missile is further away than its emitted light. When do they see the "boom" and when do they see the missile just before it reaches the "boom"? Do they see the missile _before_ or _after_ the "boom"? Do they see the missile _before_ or _after_ they launch it? Which events are seen in which order? When the missile is _halfway_ in between, is that seen before or after launching it and before or after the "boom"?
Seriously, try to write these events down in order, the missile must be traveling backwards in time to make it all fit together.
As soon as an object moves faster than light, we ( our eyes ) will stop seeing it.
Not because its too far away, only because of the reason that we SEE things.
We see things because some light was able to reach the object, and some parts of that light bounced off of it and reached our eyes.
Faster than light = invisible to human eyes.
@martf1061 It emits light... that light propagates away from the thing _at the speed of light_ It's regular old *_light_* So we can see it just like any other light.
I mean light from boom still take 1 year to travel because two locations had distance of 1 light year.
Assumption 1: nothing can travel through space time that has positive rest mass at speed of light.
Assumption 2: nothing forbids space time itself to expand in faster than light speeds. (They do indeed for very far distances from us)
So if you pack the missile into a warp bubble and that warp bubble is responsible for contracting space in front of missile and expanding behind the missile could be still in its patch of space but the space could be displacing at speeds higher than c. No relativity violation! Than pretty close to the target the bubble breaks apart and the missile becomes subluminal and fires it’s engines and hits the target. So, from the point of view of anyone the missile was launched just after the bubble explodes.
There was a super luminal travel without any violation. No issues about light cone for observers.
No, this still has _the exact same problem_ It doesn't matter *_how_* you technologically accomplish the FTL motion.
And....
Spacetime in General Relativity... ok, the full explanation is going to take a long time to explain, but what your warp bubble is actually doing _is not moving a bubble of spacetime itself to a different location in spacetime_ What it is doing is "shrinking" the space in front of it, so the actual distance needed to travel is less, and "stretching" the space behind it. Yes, this destroys anything along its path. Also doing this requires several times the mass of the Sun in both positive *AND* "negative energy", which doesn't exist as far as we know. (It's like having inertial mass be a complex number. )
I have a theory, based on several other theories I've read, that seems to remove the time paradox. Imagine you are moving through time and your position is (A). (A) is constantly moving through time in a loop at a set "time speed", lets also imagine a prior time (B) moving at the same "time speed". If you were to travel back to (B) any change you made would always stay with (B) as (B) moves through the time loop but would never reach (A) as (A) is also constantly moving at the same "time speed". If, after making changes to (B), you returned to (A) you would not see any effect. Note that however much time you spent in (B) would also pass in (A). So, if 1 unit of time passes you would then be returning to (A+1) from (B+1). However, if you were to remain in (A+1) for a period of time, say 10 units of time or (A+11), then return to (B), which would now be 10 units of time to the future of when you 1st visited, or (B+11), you would see the effect of any changes you made.
I didn't really follow this, because everyone travels through time at exactly one second per second (in inertial motion, i.e. no acceleration (long story)) That's just it... It's always one second per second. Where Relativity kicks in is that every location in space is also a _location in time_ and every location in space is in _the past_ of every other location in space. Yes, both ways symmetrically. Everything is in the past of everything else, and the further distance away something is in space is exactly how far away it is in time (in the past).
The only way two things will ever be "at the same time" is when they are "at the same place".
So, if you have two clocks located at the same place at the same time, you can synchronize them to start counting seconds together, 1, 2, 3, etc.
If you take one (or both) of the clocks and move them around through a different path in space, you also move them a different path through time. The clocks still tick one second per second, but when you bring them back together, they will have counted different quantities of seconds _because they traveled different distances in time_ and space from the first time their paths crossed to this second time their paths crossed. (That's all those "Twin Paradox" setups.)
If the clocks are not at the same location in space, then what is considered "right now" (the same numbered clock tick) is the 45° lines of their "light cones" on a Minkoeski diagram. Also, the -45° or 135° diagonal lines. Both are equally valid and you can't say that either clock is "before" or "after" the other clock as long as they are separated in space. (Seriously, events within the time window duration equal to their distance in space in light-speed units, can *not* be definitively ordered into "cause" and "effect". Any order is valid within that duration of time. (The window is of course zero when the clocks are zero distance apart, hence why you *can* synchronize them then.))
@@juliavixen176 I understand your confusion. I's a hard concept to explain in a format like this. Imagine a film reel every frame on that reel a snapshot in time. Each frame a separate reality, one that has its own past and its own future but following the same path. So, there are an infinite amount of you, each a slice of time existing in their own frame and moving through time at the same speed, so 1 second ago you, you and 1 second in the future you never meet, present you is always present you, moving through time. So, if you were to travel back 1 second in time you could meet your past self without creating a paradox as that self would be its own present moving through time and would never reach "your" present. Any changes made by you would remain in that present and if you were to return to "your" present you would not see any changes that you made nor would you suddenly have a memory of being visited by your future self as it would have never happened for the "present" you. Your "present" however would now have moved into the future by the same amount of time you had spent in the past and were you to return to the same exact time you left that would actually be a different reality, in the past relative to your actual present.
Lets now consider how the light from the explosion will interfere with the incoming light from the missile --
Will the interactions between the light give you a "hologram" of the cause and effect inside 1 piece of film ??
I don´t understand why it matters that causality is broken to observers as long as its not broken from the cause and effects "reality" as observed by them.
Even if something as in the example is launched 4xFTL in a 1LY distance, the message from an FTL observer to the effect would still reach the cause from the cause point of view after it has acted no matter how fast the message was transmitted.
I've been binging physics content for 2 days because I have the same issue. If an observer is subjected to space/time dilation and causality is broken for them, why does it matter for everyone else not subject to that space/time dilation and for whom causality is not broken...
Hey everyone, in Relativity, if you see light from something, it's really actually physically there interacting with you. It's not an illusion or a recording or something. When you see the FTL missile flying backwards from the target to where it was launched, _it is actually really there_ You can shoot it with a powerful laser beam after it has detonated at the planet, but before it has been launched, and destroy the missile in flight before the missile has destroyed the planet after it destroyed the planet.
To explain causalty you need to explain lorentz length contraction in detail. Without it the understanding wouldnt be complete. It is not like the causalty is "perceived" to be broken from the spaceship point of view but actually broken. Which can have an effect on other observers in other frame of references
When an object travels faster than the speed of light (or the speed of causality) it surpasses photons, thus after reaching at the destination, the effect would get hit by those photons (which were lagged behind, due to faster travel), thus revealing the effect first than the cause. An observer would see a "delayed" future of an object travelling at the speed of light (or causality). That's my take on the faster than light travel.
PS: I haven't yet watched the video, this is my initial understanding over this topic. However, I will be watching the video, for my future.
I mean we are talking about an impossible event so if impossible event occurs things happens where human brain can't comprehend
Like we get infinite voltage if the rate of change in current in just a small capacitor increase abruptly like in time period of 0 according calculation hence whole universe will be destroyed because of this which is an impossible event
YOUR SHIRT IS AWESOME!!!!
This video delves into why Einstein struggled with quantum mechanics. It suggests that when one electron's spin changes, its entangled partner responds instantly, potentially disrupting causality and challenging the speed limit of light, which Einstein proposed in his theory of relativity.
since Schrödinger's equation doesn't have a "c" in it....its not surprising there's no "c" limit.
None of this is an issue if you consider that physical interactions are symmetric over time, so any "effect" is mathematically consistent with being a cause. What the FTL ship sees is debris in space coming together in just the perfect way to form a moon and a missile, which travels backwards, collecting exhaust, until it slides perfectly into the launching tube of a destroyer. Entropy has been reversed, but no other laws of physics have been broken.
Consider if the FTL ship tries to "prevent" the missile launch by firing something like a brick wall into the missile's path. Then from the astronaut's perspective (who's moving through time "normally"), debris from a wall will appear to spontaneously come together from all directions in space to form a missile.
Issues only arise from the assumption that agents have the "free will" to change future events and a desire to say entropy can only increase/decrease one way.
Put even more abstractly, the common sense notion of causality creates an asymmetry in time, where past events can't be changed, but future ones can. But the mathematics of physics have no such asymmetry, only a requirement of continuous change between states. You can tack-on the second law of thermodynamics, but that relies on a sense of probability that's not causal.
I want to rewatch TENET now...
More like time appears to be moving backwards, much like being inside a moving train.
Now here's a thought experiment, have the train grow or shrink and see how object appear to move both on and off the train.
And the reverse is true, too. If a phenomena requires a reversal in time, it breaks the special theory of relativity. This happens in certain double-slit experiments.
The speed of light in a vacuum is the speed of causality which is why it can’t be exceeded or causality broken
I really enjoy your videos... I am learning a lot from them :)
Those causality circles are really just cross sections of light cones, aren't they?
Yes
These are some of the best physics explanations there are. Period.
Also, what does the shirt mean?
10:06 but it should be 1 light yr. Only. because in your 'why can't we still reach the speed of light ' video you said that even after length contraction every observer will agree on the distances because the measurements too will get length contracted and the distance will be the same so it should only be 1 lyr. but why isn't it so ?? Why is it 3 light months ?
In my opinion, this kind of paradox arises not because of ftl but because of trying to preserve causality in the causality-broken world.
Causality means an effect cannot happen prior to a cause, but it also indicates that an effect needs a cause.
If causality were somehow to be broken, an effect would take place before the cause, but also means that a cause doesn't necessarily need for an effect to occur.
Preventing the launching of a missile that would explode the moon after the explosion becomes a paradox when we think not launching a missile contradicts the explosion.
In other words, it becomes a paradox because we assume not launching a missile should influence the explosion, preserving the causality of missile launch→explosion.
If causality is violated, it is not strange that an explosion happens without any cause because that is what "causality is broken" means.
Therefore, if an ftl missile hit a moon and prevented the launching afterwards, the cause got deleted from history and the moon still remains destroyed without a cause (because causality is broken), so no paradox.
It seems to me that, all the emphasis is placed on what different observers will see. Regardless of differing perceptions due to proximity and speed, the cause, in and of itself, always occurs before the effect. A person cannot be shot and wounded by a bullet before the trigger is pulled.
Scenarios to the contrary, defy the logical linearity of observed reality which underpins our understanding. Could it even be possible to explain how an effect came into existence before its cause?
Quite easy to understand. However, I still see that the spaceship is just seeing like it happened in reverse, but not how it really happened.
This is actually interesting topic ("see" vs "happen"), quite a few videos on youtube mention that relativistic length contraction is not the only thing you will "see" (with eyes) when something passes by, you also will see this object turned due to speed of light having limit - this distortion has nothing to do with relativity. Look for "Optical effects caused by the finite speed of light"
In animations here, I guess, what spaceship "sees" means when the light circle emitted by some event reaches it, whereas what "actually happens" is what we as viewers see happening during this animation, while observing "from the side".
Relativity is a very "what you see is what you get" theory, and most of the popular science entertainment explanations of it are terrible. The way it gets presented outside of an actual Physics class just confuses most of the audience. Relativity really is very logical and straightforward, but the pop-sci version is a muddled mess. Like the game of telephone, the source for pop-sci entertainment is _other_ pop-sci entertainment.
Then I guess it’s not so easy to understand.
Questions:
Why do we ignore the light that is being emitted as the missile travels through space?
I understand that the observer sees the missile being fired and the moon being destroyed at the same time, but wouldn't they also see the missile destroying the moon since the light being emitted from the missile reaches the observer at the same time it's being destroyed since the missile is at the moon at the time of it being destroyed?
Wouldn't this phenomenon make it look like the missile was being stretched across space instead of seeing it in one place while another thing happens because of it?
For example, if the light at the time of the missile being fired and the light when it hits the moon arrived at the same time from your perspective, wouldn't it look like the missile was stretched across the entire lightyear of space in an instant?
Wouldn't it then look like the missile reached the moon instantaneously from the moon's perspective by stretching across the entire lightyear of space?
Speculation & Thought Experiment:
I'm thinking, what if space contraction happens because of the fact that the information you observe is more frequent in the direction you are traveling and less frequent in the direction you are not?
What if light moves at a constant speed no matter the perspective because light is just the speed of information for any interaction in the universe and not the speed limit of information itself in the universe?
This would mean that if any particle were to interact with any information that was traveling faster than light (or at any speed at all relative to it) that it would only be effected by what it receives from that information's light speed emissions; making it look like the information was being stretched across space (due to a perceived space contraction from the particle's perspective) while being hit with a different frequency of information (due to the particle receiving information faster than it can interact with anything else in the universe. This includes spacetime, so it also causes the perceived space contraction and time acceleration).
This includes the emissions of information (even at light speed) coming towards you as you approached the speed of light. Information is indeed coming towards you at a faster speed than light, but since you can only observe the information's light speed emissions, and interactions between particles operate at light speed, from the perspective of every object traveling with you, everything would be observed to have more information/energy (as the information received from every field of the universe including spacetime would be observed to be compressed or at a higher frequency when it is received), time would be observed to move faster, and distances would be observed to contract.
I believe this would allow faster than light objects to exist in the universe without breaking causality. If this works, this also gets rid of the "Universe conspires to keep things below light speed" weirdness that special relativity currently has. It would be that way because faster than light speed literally could not be obtained unless you already had some field that could accelerate information to something faster than the speed of light since the speed of interaction in all fields of the universe are capped at light speed. Like black holes for example.
It makes it easier to understand once you realise that the speed of light = the speed of causality.
I really wish that it had been called the speed of causality (the word would even match the letter c used to represent it in equations), because calling it the speed of light has led to people thinking that light has some sort of special status as a conveyor of causality, but it's actually the other way around. Lights moves at the speed it does because that's the speed at which causality occurs. Of course we didn't know about causality and relativity when the speed of light was calculated, so that's why it was named that way. A pity really.
Sabine has a video saying that this isn't true. Have you seen that? Would love to see you two sort that out.
I've seen a lot of Sabine's videos, and I don't remember her ever saying this. But maybe I'm mistaken. Which video of hers is it?
@@juliavixen176 ua-cam.com/video/9-jIplX6Wjw/v-deo.html
Every effect is caused by something previously.
To every reaction, there is a previous action.
But every actions are in fact, reactions to previous actions, that are reactions.... So on and so on...
Therefor, CAUSALITY CAN'T "REVERSE".
You turned my world upside down !!!
Okay, now I understand the movie Tenet!
I didn't know that the third derivative was called a jerk. For some reason my calculus prof never mentioned it.
Causality is god, at least in our universe.
Wonder what will happen to this sacred notion if the fabric of spacetime is proven to be made up of tiny wormholes connecting entangled particles, as suggested by some theories.
Great video. Thanks, looking forward to more.
Captain: Target the moon 1 light year away.
Gunner: What moon?
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There's a Sabine Hossenfelder video about ftl not necessarily breaking causality, what do you think of it?
I think that's somewhat clickbait, but at the same time, because there is not a combined theorem of GR and QM. We can't be *absolutely* certain.
She is a failed physicist but she is funny.
This is the best physics channel
Have experienced this with sound standing next to a rifle target being shot at a huge distance. You hear the bullet hit the target before you hear the gun fire.
In the same way the lightning (effect) arrives before the sound of the thunder (cause)
Here is the loop hole buddy. The blue ship can only see the boom effect after rocket hit the moon. And for rocket to hit the moon, shooter need to launch first. So, even rocket reach instant to the moon, shooter already press the button and launched. So, whatever blue ship people try to say the shooter, it can't stop because hitting button and launch was first event before boom effect. So, causality didn't broke.
Can we use the common housefly analogy here? From the fly's perspective or from its reference frame, things are very slow, like 20 fps, but from a human eye, the fly is flying faster, and thus, it is tricky to swat. I know Einstein is a poor analogy, but it's worth trying. 😁
From the perception of the ship moving away from the launch, how much of the light would be red shifted?
This video considers light as the transfer of signals but in information travels at infinite speed the space ship would know when the roket launches . Hence it information travels at infinite speed everyone would agree on same think .it would just be a matter visuals
Q: Why do faster than light signals break spacetime?
A: No: it does not happen. If it did, then it would be time-reversed.
So if we had a wormhole portal that could travel faster than the speed of light it would be possible to change the past, very intriguing.
Yes, this was one of the first things Kip Thorne published about wormholes.
This video is correct about FTL signals reversing cause and effect, although the presentation kinda burries the actual reason in a bunch of descriptive stories.
It's a bit easier to understand the problem with "FTL anything" by analyzing a FTL round-trip journey between two distant locations in space. To make a long story short, observers at each location will see the FTL thingy come from the distant location's own past... _Both_ ways!
If something goes back and forth FTL several times, it will time travel further and further backwards in time each trip.
I'll write out a long explanation of this if anyone here wants to read it.
I'd love to hear the explanation
@mistersadfaceman4257 Woo-hoo! I should have prepared some text beforehand, but I'll try to summarize the important things. (I'm in a hurry at the moment and need to be doing other stuff than writing right now. )
Things to know about Special Relativity:
• Every location in space is also a location in time.
• When you look in a straight line directly in front of your nose to the distant stars, everything you see and feel and can effect you in any way *_right now_* is the 45° surface of hyperspace "light cone" on a 4D Minkowski spacetime diagram. (Like slicing a 3D cone into circles, you are looking at concentric spheres centered on your eyes, and spheres are slices of a 4D hypercone. It's a 45° line on the regular 2D diagram everyone draws in books and videos. )
• What you see *_right now_* is the past of everything everywhere else in the universe.
• Everything everywhere at every location in space is also located in the past of every other location in space. Your feet are six nanoseconds in the past from your head and your head is six nanoseconds in the past from your feet. The Moon is 1.2s in the past of Earth, and Earth is 1.2s in the past of the Moon. The Earth is ~600s in the past from the Sun, and the Sun is ~600s in the past from Earth. The Earth is 2,537,000 years in the past from the Andromeda Galaxy, and the Andromeda Galaxy is 2,537,000 years in the past of Earth...
... _right now_
• If you flip this around, every location in space is also located in the future from every other location in space. This is if you count t=0 as everything you can see *_right now_* which is everyone else's past.
• This is symmetric, both ways.
• The _only_ way for two things to actually happen "at the same time" is by being located "at the same place"
• Syncronizing remote clocks is a bitch.
• There is a gap of time between any two distant locations in space, equal to the amount of time it takes for light to travel between those two locations, during which events do not have a strict cause-and-effect ordering. Event "A" at one location and Event "B" at a distant location can occur "before", "simultaneously", or "after", each other if they both occur during this time period. (It's the diamond shape between two light cones on a Minkowski diagram. ) All arrangements are valid, because who gets to be called "right now" is an arbitrary choice.
• Oh, I should mention: Everyone and everything's own "proper time" clock always ticks at exactly one second per second, _always_ no matter what they do. Time dilation is everyone else's problem.
I think that's most of the basics. So, everyone's current moment of *_right now_* is synchronized with light (or any kind of light speed signals, but light is the most practical.) Everyone arbitrarily chooses whether or not they will align their own current "right now" time to be named the "past" or the "future" on someone else's clock.
Alice and Bob are located on planets or space stations or whatever, four light years apart. Let's pretend that they are standing still with zero relative velocity with each other to keep this simple.
Alice broadcasts a radio message: "At the tone, it will be 00:00:00 January 1, 2000... *BEEP* "
From Alice's reference frame, Bob will receive this signal on New Years Day 2004 _on Alice's own clock_
But Bob sets his clock to match Alice's clock. So the instant when he receives Alice's radio signal, _it _*_IS_*_ Jan 1, 2000 for him_
(Back to Alice for a bit) When Alice was broadcasting that message on New Years 2000... from Alice's reference frame, it was "currently" 1996 at Bob's location.
Ok, got all that? Here's the thing: This is symmetric. Swap the names "Alice" and "Bob" in the text above, and it's exactly the same. It's valid for either one or even both to decide when to set the "zero" time to start counting seconds from. They could even use a third location halfway between them, that doesn't change their timekeeping situation.
So, Bob declares that it's "now" the year 2000-Bob-Time, and so Alice is in 1996-Bob-Time. Alice declares that it's "now" 2000-Alice-Time and so Bob is currently "right now" in 1996-Alice-Time.
You can slide these scales back and forth however you want as long as the offset _is less than four years_ As soon as light can get from Alice to Bob (and the other way) the order of cause and effect becomes frozen into a single reality... because they have both been "at the same time" for each other's "current time right now".
If a Baby is born on Alice's planet in 2001-Alice-Time, that's 1997-BobTime. If a baby is born on Bob's planet in 2002-Bob-Time, that's 1998-Alice-Time. Which Baby was born first? The answer is that it is valid to say that both babies were born before, simultaneously, or after each other.
If a Baby is born on Alice's planet in 2005-Alice-Time, that's 2001-Bob-Time. So, a baby born on Bob's planet in 2000-Bob-Time *IS* born _before_ that baby on Alice's planet. (1996-Alice-Time)
Cool, got all that?
Faster than light signals travel from the future to the past. They outrun the t=0 "right now" present moment synchronization that keeps cause and effect and "the present instant" in order.
When Bob receives Alice's radio signal, he's hearing it live, exactly as it is broadcast "right now". It's not a recording, it's really happening.
If Alice transmits a Faster Than Light [FTL] signal to Bob in 2000-Alice-Time, and Bob receives it in 1998-Alice-Time.... and then Bob immediately replies with his own FTL signal back to Alice. Bob is broadcasting his FTL signal in 1998-Alice-Time... which should be 1994-Bob-Time... which means that Alice will receive Bob's FTL signal in 1996-Alice-Time.... *_Four years before Alice broadcasts the original message in 2000_*
(I did this math in my head, and so if it's off by 2 or 4 years: oops! But the round-trip time is always negative. )
Slower than light round-trip: positive time length
Light-speed Round-trip: zero time length
Faster than light round-trip: negative time length.
I have to go do other stuff. Ask if you have any further questions.
@@juliavixen176
Okay, so I think I understand now. Thanks
I am so happy to figure out your shirt (a friend coincidently discussed it too) Hint: it's a third derivative of distance over time
I have a question. When the distance becomes 0, it was said that it did not matter what we divided by. What about dividing by zero? Doesn’t dividing by zero (0/0) break the math here? 25:42
So FTL breaks causality… but what what about faster than sound travel? If you take the same thought experiment, but replace the FTL missile with a supersonic one, have the stationary observer LISTENING for these events rather than looking, and have the moving observer traveling near the speed of sound and also LISTENING for these events, wouldn’t the same paradoxes arise? (Also assume it takes places in a medium like air that allows the mechanical sound waves to propagate.)
It could possibly. This guy made an error. The most important part of this theory is not the observation but the communication. So, say this FTL missile is being fired, and you observe it in t time (light reaches you)... Since you can travel/communicate in FTL speeds too, you can send a signal/warning before t not to fire the missile in the first place. And since your communication is FTL, when your communication reaches the missile, it won't have left the airport/wherever they keep missiles..
There's a better demonstration of the issues with FTL that wasn't mentioned in this video. If a round-trip is done by something moving faster than light, it will arrive at its departure location *BEFORE* it originally left.
In addition to what others have said, there’s also the length contraction aspect. When he’s playing around with the circles at the end, he uses the fact that the blue ship is traveling very fast to create length contraction such that the yellow circle is bigger than the green circle. The fact the yellow circle is bigger shows that the yellow event (explosion) actually happened first.
If you’re moving fast enough for meaningful length contraction, none of the sound signals will ever reach you.
Ok, but assume this is done with some sort of space contraction so we don't literally have all the relativistic effects (seems to be somewhat of a loophole to relativity) the demonstration that you could get to the source faster than the launch just doesn't automatically happen. If you did go faster than light towards the source the light reaching you would also accelerate even though your perceived (watch time) would not. The return trip would take the same time as the initial trip of the missile and half of it would be after the light from the missile launch has reached you, assuming 2x speed of light.
There is only 'Now'. There is no physical past and no physical future. If we want to graph some physical event - say the position of a falling rock then we put the hieght on the Y axis and we then have to use a clock to tell us when to take each record of where the rock was. We do this by taking a snapshot of the rocks position as the clocks pointer passes each second graduation (say). Now the thing that all scientists miss is this. The Y axis ONLY shows the hieght of the rock, nothing else. The x axis selects which of the snapshots of 'Now' that we want to see on the graph, in this case, we are most interested in the rocks position. But pull back and look at those snapshots again.... What else was captured? Well, the state of the entire universe was, literally everything. You can happily plot the path of anything on the same axis, an ants depth, the rotation of the moon, the temp of any star you like. That isn't a feature shared by hieght, voltage, pressure, light intensity or any of the SI units, time is different and though you can assign it as a 'variable number' in any maths equation, it can't be used like that in real life. Time is the same everywhere, it has to be, it is just a snap shot of everything at intervals dictated by a rotating mechanism. (Oh, and the clock isn't 'measuring time, it is dictating it.....)
So, it seems the most impressive thing we will ever see in our universe is the death star laser!
We will witness the explosion and firing sequence simultaneously.
where do you get these type of t shirts bro?
I’m unable to ascribe a physical (as opposed to mathematical) meaning to the missile launcher’s FTL signal to abort the launch arriving at the launcher before the launch but after the explosion. I realize this is the paradox but the argument feels tautological like: assume false (not something we want to show is false but rather something clearly false by definition), then show false is true, and therefore argue that false can not be true (which we always knew).
One could in principle conceive of multiverse theories where there is no paradox.
As I was saying tomorrow in my lecture on reversible time...
I can't help but to compare speed of light with speed of sound. There might be mathematical explanation but intuitively I don't understand why crossing a speed of one wave is feasible and aleady done, but other is not possible even in theory.
Remember the aliens from the movie the quite place? They don't have eyes but have very sharp ears. They "hear" the universe the way we "see" the universe. If we take the entire experiment in air or some medium and scale everything down to speed of sound and read sound waves rather than light, shouldn't those aliens be concluding that going more than speed of sound breaks causality?
@@paragchitnis7616 all other waves travel through a medium! So, they are carriers of oscillations of ‘things’!
Electromagnetic waves travel in vacuum with noTHING vibrating! That’s what makes them special!
I am having trouble understanding why it is not an illusion if the missile is not time traveling.
As far as I understand it, we believe that the maximum speed of light is the speed of causality (I'm think speed of causality is what is meant by speed of light in this video) because nothing (that we know of) is capable of carrying information faster; however, with this question, we assume that something CAN travel faster than light, and that thing carries information about its origin to its eventual destination. So would this not imply that we altered our definition of the speed of causality to be beyond than the maximum speed of light in the first place? As far as i understand it, there is nothing to really tell us we cant, it just isn't particularly meaningful to do so (that is unless super-photonic information transfer is possible, which this question assumes is the case)
It seems to me that we presuppose the maximum speed of any causal relationship, and ask what happens if something carries a causal relationship beyond that, similar to defining the north pole as the northern-most point, and asking what happens when you go north from there: the question breaks down. If we assume that we CAN still go north in the question, then that means that we have hidden the fact that we altered the definition of north when we asked the question.
TLDR: My intuition tells me I'm understanding something wrong or the question is flawed, and it has me confused. 😖
0:42 I'm pretty sure I've seen the leader of a certain country, somewhere on the interwebs, bragging that his country had missles like this in service already...lol