you all prolly dont give a damn but does someone know a method to log back into an instagram account? I somehow lost my account password. I love any assistance you can give me
As usual professor Brian, your exposition is brilliant, and despite the intricate of the subject, you make easier understandable. My sincere congratulations.👍
What really excites me about Brian is the fact that parallel to the speed with which the universe is expanding increases so does his urge to share knowledge and teach. Whether it is the science that flourishes such noble feature in a human or one is borne with it I don't know but its people like him that makes our species worthy of the evolutionary path we have had!!
Thank you for the daily dose of equations! It is something I look forward to. As an artist inspired by science, your explanations provide a wonderful description of the cosmos and have inspired a number of my pieces. Thank you!
Professor Greene - good on you, love your talks! Hope one day, you can do a bit on Paul Dirac and how he used projective geometry to come up with his ideas.
Yes Dr. Greene is a beautiful thing when you can imagine kids minds exploding as they realize what they can get out of scientific equations! 🙏🏻 Thank you always for such great content!
I’m one of “ those kids” who love this stuff! Finally in my 71st year you came along to explain it ! So stop drinking out of plastic water bottles - Ffs!!!! I wanna hear ‘bout negative gravity(what? really? ). The vector on a curved surface feels like cognitive shift in my mental data base. I reviewed it a few times- might have to appropriate a basketball from the neighbours kid😜. . I keep recommending your videos to my friends. My circle of friends appears to be getting smaller! At first glance your vector example of 2d compared to curved space is like a metaphor for my life. I start at the same spot as everyone and end up facing a different direction. Love it that I can now point to a mathematical equation to account for my obtuseness! I’m in a different dimension! Truly a ‘space cadet’. Ha ha! Thanks - so fun, love rubbing neurons together..
Amazing explanation as always professor Brian! Just learned how the expansion of the universe is derived from Einstein's field equations! It's simple priceless! A thousand of thanks professor!
Hello Professor Greene, this is Valdo from Rome, Italy. "Your Daily Equation" represents a great idea to share and promote complex scientific events and ideas with common but passionate people all over the world. Hope in the future you will take a closer look in the fundamental intuitions and equations of Strings Theory, and use these steps to finally describe its state of the art.
@@frogz technically one class is not the same as "some" of his classes, I will attend more however, but you are right, I did just attend one .I was actually reminiscing on when I attended collage 46 years ago, wistfully comparing the education we received back then, to the advanced classes like this one that are available in scholastics today. Cheers mate! Thanks for the comment.
Thank you for doing this; very kind. By the way, I attended a lecture/book promo of yours in Ann Arbor, MI, many years ago. I still remember your ability to break down complex ideas so that they’re understandable.
Thank you for the history of the development of modern physics. You sure have a gift in translating the technical “silo" language of Math & Physics into a fine novelist’s narrative that is clear and captivatingly inspiring
Professor Greene your explanations during this series always amaze me and thank you for your ability to provide insight into what I am sure is a very complex subject, but in a way that everyone can understand and learn from!
🤯 every episode is fantastic. Thank you for continuing to give such insight to these concepts! I really appreciate you breaking down the equations and showing how work towards developing an intuition when going through them.
Thank you so much. In this pandemic era I am learning so awsome things. I going back to my early days as an student. I think now I have time to pay attention and understand these concepts. I understand that the universe isn't an explosion, but an expansion. Thank you.
These ideas are indeed very hard to reconcile with, to come at friendly terms with. My mind is a hot dense quark gluon plasma of questions and perplexity right now. Thank you so much once again sir.
The balloon metaphor is my favorite one in all of physics. The metaphor does not go far enough. The surface of the balloon represents the three D manifold of our spatial dimensions, but the area under the surface represents our PAST. The area the balloon is expanding into is the future. Here, we can actually visualize time as a three aspect spatial dimension. Like a black hole, the information content of the of the universe is a function of it's surface area (The present.) The area outside the balloon which the balloon is expanding into is the higher vacuum of utter nothingness, our FUTURE. The area underneath, the Past, contains nothing but the dark energy which is what is blowing up the balloon. The surface of the balloon is comprised of the Higgs field and either/ or Dark Matter. The fabric of the Dark Matter would super strings of string theory. One caveat of this balloon analogy is that the universe is likely expanding to a minimal surface area. Whatever that minimal surface is, it could lead directly to the big rip once it is reached. Pop goes the weasel.
thank you professor Greene, it's been really an inspiring episode, a journey through beautiful equations giving sense about universe expansion and its infinite density at a point, of origin back in time, of big bang but i didn't get the point of considering, of why, that the scale factor a(t) is being related to certain power law, 't to the power alpha' i mean i didn't get the base reason for such i mean why not the exponential law which equals unity at time zero. or maybe i sound silly to ask such.......well i hope professor i'll be getting the answer soon. Thank you
Basically, because he knows the answer, and doesn't want to waste time going down false trails. As for why not an exponential, we can see that the universe is not expanding exponentially.
yes professor you are right how can be something like infinite density. it is just that the amount of matter and radiation are so huge that it is quite difficult to express in form of numbers.
Thanks Pr. Greene for this great series. I am facing a paradox with respect to this last one: does the metric of space increase with the space expansion? if I were to measure now the distance between our Milky Way and some Galaxy using say a standard stick the number of those sticks would be the distance. If I were to repeat the experiment some millions of years from now I would need some more sticks because of the expansion of the Universe.... provided the sticks themselves do not expand with the universe. However when you mentioned the density of energy for radiation it depends on 1/a^4 and not 1/a^3 because the radiation itself expands with the universe: does this mean that the measuring stick does expand with the universe? then how come we can measure the space expansion?
Question: Does it take energy for the Universe to expand? If it does, does it mean the expansion will not be infinite? If it does not, does it violates any conservation laws?
conservation of energy doesn't really apply to an expanding universe. Conservation of energy requires a closed system. Expanding universe is not a closed system. Your question about what energy is driving the universe is exactly what people call dark energy. No one really knows what it is, hence the term dark. If the dark energy were to somehow run out, then the universe expansion could slow down and perhaps stop.
I consider that the boundaries of the universe are determined by the propagation of fields - likewise I believe dark energy/dark matter are in fact regions of space that are perhaps sharing dependencies but not completely attached and as such we are presented with a region of unknowns...
If I attempt to draw just 3 lines that meet at a point; I usually miss -- and end up with some tiny triangle in the center. Hubble's observations (and also modern observations) don't seem sufficiently precise to justify the strong statement that, winding the clock back, everything in the observable universe would meet at a single point.
They don't just eyeball points on a graph to figure out the expansion rate, they use statistical techniques to get that, based on the data and the errors in the data. The result also has an error.
We are told that the date for the birth of the universe is calculated by working back using the speed of expansion now. How do we know that the expansion rate of the universe has always been constant? Can anyone out there help me with this question?
3 роки тому
"let's see an example about the whole universe" -----> me, moving towards the monitor even more while putting on the rarely used glasses
Hello! When Einstein spoke about the static Universe, it is true... We know periods of expansion, dynamism, but also periods of conservation of energy to give rise to other atomic structures.. Thank you!
The beginning started for me to understand the subject so cooling with real ZEAL to educate not only children but we oldies as well who have dumped all somewhere.
I brought my son in (10yr) to watch the R connection transform as I thought he would like it. he went and got a Dice and showed me that he noticed that if you start at the six and turn it across 1 down 1 and back to original, then the six dots have turned on there side, then he told me he had noticed this and that he thought it was a non Euclidean plane.. I dont understand what he means but he explained in graph form what is happening. I still dont get it, I cant do maths
Wonderfull pedagogy, thank you! I have a question : since (global) curvation arises from the (local) metric, wouldn't a metric depending on a single scale factor (when applied to the entire - isotropic and homogeneous - universe) give rise to a null curvation overall ? But you said the 3 scenarii (k=0,1,-1) would be compliant with the isotropic and homogeneous hypothesis, so I must miss something .. I tried to resolve this by realizing a(t) just sets the relative change in distance between any 2 points over time, and this can be applied to an universe which have either k=0, k=1, or k=-1 to begin with. Maybe I'm confused because a metric depending on a single scale factor does not mean having a metric reducing to a simple diagonal matrix or something ...
Thanks Prof, I enjoy your daily equation. I am trying to reconcile this idea regarding the universe being infinite. If the universe is considered to be infinite, then how could it be explained that it is expanding? How can infinity be added to?
Its expanding only in the sense that the space at every given point is expanding, but in an infinite universe the boundary that contains it would not be expanding because this boundary would not exist.
If galaxies that are 'far away' (a long time ago) look like their speeding up... wouldn't that mean that they were going faster previously, and therefore it's possible that they are no longer going at that speed? And could in fact the universe be compressing, but the compression of light just hasn't reached us yet? My brain hurts.
Q: If there is a redshift of light in the universe because of distance, then galaxies that move away with constant velocity seem to move away with acceleration. If so, the bigbang-theory is possibly wrong?
Can it be possible that when a star's core has enough energy that it smashes the particles at such energies as that before the higgs field turned ON, (then according to the same theory) the particles were massless, all 4 forces were unified and therefore the star collapses to make a black hole. Thus, light cannot escape from the black hole as the forces are combined, and light is overpowered. This also verifies that most black holes need to have a high mass, density in order to cater to the energy needs. And because the higgs field is the PROBABLE reason for asymmetry between particles and anti particles, with the higgs field off, there is perfect symmetry, the particles annihilate each other, leaving nothing detectable with the STRONG unified forces on top. And because all the mass, particles have been converted to energy, energy bends spacetime, therefore we experience a "gravitational" pull. Classical physics does not account for a unified force and thus our physics breaks down at the blackhole.
_The universe itself keeps on expanding and expanding_ _In all of the directions it can whizz_ _As fast as it can go, at the speed of light, you know,_ _Twelve million miles a minute, and that's the fastest speed there is._ _So remember, when you're feeling very small and insecure,_ _How amazingly unlikely is your birth,_ _And pray that there's intelligent life somewhere up in space,_ _'Cause there's bugger all down here on Earth._
With my no education and very limited intellect, it's no wonder that reading explanations of the cosmos gives me headaches. My question is this, if the universe is expanding, things are moving away from things at terrific speeds, then what we see is no longer where it was light years ago. So, are all objects currently in a different direction from where we now visualize them, either to the right or left or up or down, or are they in the same place only further away?
IF we shrink all matter, compress to fit that infinitesimal size, would all the known mass/things in the universe fit in that "point"? I always imagine that shrinking all the universe to a singularity would not be a infinitesimal point, but something that would be visible because all that there is would not "fit" in a point. Are there calculations like that?
Initial mass is assumed to be something like planck mass, initial size of the universe something like planck length, and so on. Then somehow during inflation the rest grew out of nothing... you can see from my explanation that I am also still learning. And I am more and more convinced that this question still is not answered finally.
Where we are it would be really really dense. But there are still places that infinitely far away that are also very very dense. At least in an infinite universe. And people tend to think it is indeed infinite in extent.
We need a theory of quantum gravity to answer those questions. That's one of the problems with relativity, it breaks down when you smash things really close together. And quantum mechanics doesn't explain it very well either because it doesn't include gravity. All we can say is that at a previous time the universe was in a more dense state than it is now. What that ultimate density would be like nobody really knows. Our equations break down into infinity at that point, so in less infinity is real, which most physicists don't like, we just don't know.
You caught my attention, and I want to watch a few more of your UA-cam videos. I hope someone can explain a few things to me. I’m not sure if that will be you. I like the thought that things have purpose that we have what we have, and they are there for a purpose. Otherwise, there is no purpose. I have many questions about black holes: What is the Natural purpose of black holes? Why do they exist? If they existed for such a long time wouldn’t they have gobbled everything up? Have we ever seen evidence of a black hole exploding as if it were creating a new big bang?
This does not make sense. The expansion of the universe is faster the further away from us, as demonstrated by the balloon: from our spot, going from 1 unit away now is 2 units away; however, if the point of view is at the opposite end of the balloon, would triple distance away. Seems it all depends from our point of observation.
I don't see where the triple away part comes from. You're not seeing the analogy correctly. No matter where you are on the balloon, everything expands away from you at an ever expanding rate. Personally I wish people wouldn't use the balloon analogy. Because balloons are three-dimensional and that misses people out. It's easier to see just on a flat sheet that stretches out and expands. It makes more sense that way. there's lots of good videos that demonstrate how there is no center to the expansion. You can look some of those up.
@@dankuchar6821 I agree a flat rubber surface as our universe is flat would be a better analogy than a balloon. However, the Hubble constant is a constant expansion of the universe that increases the farther away from us. This I do not understand if it is constant. So, it must be some optical illusion. As it is 3 units away from us, in the balloon analogy, and doubles in expansion to 6 units away. So, one unit away from us will now be twice away. Constant expansion of doubling. This will give us the red shift which is an actual physical observation. We do not see "space fabric" itself expanding. What makes more sense to me is that space does not expand, but all galaxies are being pushed at the same Hubble constant.
The problem with the baloon example is that the "galaxies" ( purple squares in the example baloon) also grow in the same proportion in relation to everything else, so to them, the distances are all the same. It works to someone siting outside, but it is not the case to them. Or us, if we were on the "baloon".
Thanx brian for the info and the place to share ideas. - At time 9:00 there is a hubbles diagram that show how supernovas follow a pattern as how they are expandding but Brian needs to say that at the right up corner at the end stars no longer stand in such patters anlist that is what the phd says in the video: THE MISTERY OF DARK ENERGY THE VON CARMA LECTURE SERIES 2008 at time 20:13 more resent supernovas picture, he says that; take a look to the north right side and notice how the system in which the supernovas are found make un up curve kind of the system opens almost from the bigening from the center to the right top side, the north side is the one that always opens the most in all systems as well our sun has the corona on top north side, is been noticed that at our suns corona gases and matter speeds up when just lieving the suns electromagnetism at the suns corona so my guess is that such speed up of wind speeds cause it leaves the sun that is at much grate presure than out the sun sphere. Same thing happens to the supernovas that at the point of leaving the system where they hapen to be the stars are much more seperate cause they are stars of a different level so those stars no longger fit hubbles constant.
I found out that the time reversal dosen't exactly reverses the path same as it was before for eg in three body problem then how can you conclude that the bigbang happened by reversing the time? (The same mathematical equations that gives you the path in future dosent give you the position of it it ln the past.)
What if the balloon analogy was wrong? It doesn't well capture the expansion as the entire universe isn't a plane. Implication is misconstruing of derivatives. What if everything in the universe is contracting at the speed of expansion creating the illusion of an expanding universe. It would mean our universe is actually static (as the size of the universe is constant including the boundary of the universe) but appears to create the illusion of expansion due to the contraction of everything. This causes the flow time. Opposition to the contraction causes gravity.
Photon is the only particle that does not oppose the contraction theory, that is why it moves at such speed, forms a constant in the universe and appears to be massless.
How is the cooling of the expanding universe explained? e.g. - Imaging a single particle moving at a speed v, (which is kT); what causes it to reduce it velocity?
As space expands, the wavelength of energy stretches with the expansion of space. A longer wavelength is lower energy effectively cooling the universe. So the wavelength of light expands with the universe, Even though light always moves at a constant velocity that never changes. A particle moving through space would appear to slow down as space expands around it. Those are some simple analogies, I hope they help.
If it's nowhere to expand for the universe and all the matter that universe needs to expand to is used or gone. What would be left, where universe can expand to???
You say the universe doesn't have a center, but if you were to rewind the motion of all the galaxies, they would eventually reach a point, that really does exist right now and that is located in our universe, wouldn't you?
If one were to take a skeptic approach and say that hubble redshift might arise from other unknown phenomenon, what is the tertiary evidence for expansion?
It's called a distance ladder. Before you get to red shift there are other methods of measuring distances in the universe, such as parallax and then variable stars etc. Red shift is the farthest rung on the ladder. Also one must come up with another reason for red shift. And there's no known physics that can cause photons to stretch in wavelength and lose energy except for the expansion of spacetime. There are some hypotheses, but there is little to no supporting evidence. While there are multiple levels of evidence for the expansion of the universe.
The apparent speed of distant galaxies rushing away from earth's perspective is as old as the photon travel time. Wouldn't it be more correct to say "The further the light source from the earth the faster the source of emission 'was' traveling away." (Rather than the commonly used present tense "is") Since a galaxy emitting light at 10 billion light years distant, will take 10 billion years to reach the earth for us to observe its current speed signature?
yeah i was right there when big bang happened, it was amazing, africa came out first, then other continents, all planets formed round except earth, earth emerged out flat tray shaped that's why we have life on earth,
Where does "Einstein's Constant" play into the theory of the expanding universe? Didn't Einstein make up that number so that the general theory of relativity would be consistent with a static universe and then discard it when Hubble proved the universe was expanding? And wasn't that constant revived 70 years later to explain the amount of dark energy in the universe? I'd bee curious to learn about the role of the constant in our understanding of the universe. Thanks...
When we think of a sphere, it has an intrinsic geometry, and can be viewed as a 2-dim object in 3-space, and the boundary of a solid ball. In the balloon metaphor of the expanding universe (as the surface of the balloon) ... this sphere/balloon is not the boundary of anything?
In the balloon analogy, there is not a boundary. It's a two-dimensional analogy of an expanding three-dimensional space. A famous three dimensional analogy is raisins in bread. As the bread expands while the dough rises in three dimensions the raisins get further apart from each other. The raisins would be analogous with galaxies in the universe.
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I’m so lucky to be able to watch your lectures at my age during this unprecedented time. Thank you!
you all prolly dont give a damn but does someone know a method to log back into an instagram account?
I somehow lost my account password. I love any assistance you can give me
As usual professor Brian, your exposition is brilliant, and despite the intricate of the subject, you make easier understandable. My sincere congratulations.👍
Best part about this was Brian Greene's enthusiasm and giddiness over something he's probably explained thousands of times.
What really excites me about Brian is the fact that parallel to the speed with which the universe is expanding increases so does his urge to share knowledge and teach. Whether it is the science that flourishes such noble feature in a human or one is borne with it I don't know but its people like him that makes our species worthy of the evolutionary path we have had!!
Incredible. You’re an inspiration Dr. Greene
Thank you for the daily dose of equations! It is something I look forward to. As an artist inspired by science, your explanations provide a wonderful description of the cosmos and have inspired a number of my pieces. Thank you!
Professor Greene - good on you, love your talks! Hope one day, you can do a bit on Paul Dirac and how he used projective geometry to come up with his ideas.
Chi, I just want to express my appreciation. You made me understand the basics of General Relativity more than before.
Yes Dr. Greene is a beautiful thing when you can imagine kids minds exploding as they realize what they can get out of scientific equations! 🙏🏻 Thank you always for such great content!
I’m one of “ those kids” who love this stuff! Finally in my 71st year you came along to explain it ! So stop drinking out of plastic water bottles - Ffs!!!! I wanna hear ‘bout negative gravity(what? really? ). The vector on a curved surface feels like cognitive shift in my mental data base. I reviewed it a few times- might have to appropriate a basketball from the neighbours kid😜. . I keep recommending your videos to my friends. My circle of friends appears to be getting smaller! At first glance your vector example of 2d compared to curved space is like a metaphor for my life. I start at the same spot as everyone and end up facing a different direction. Love it that I can now point to a mathematical equation to account for my obtuseness! I’m in a different dimension! Truly a ‘space cadet’. Ha ha! Thanks - so fun, love rubbing neurons together..
Amazing explanation as always professor Brian! Just learned how the expansion of the universe is derived from Einstein's field equations! It's simple priceless! A thousand of thanks professor!
And that was considered a "mistake" by Einstein..... Even a mistake from Einstein was correction in our science...
Hello Professor Greene, this is Valdo from Rome, Italy. "Your Daily Equation" represents a great idea to share and promote complex scientific events and ideas with common but passionate people all over the world. Hope in the future you will take a closer look in the fundamental intuitions and equations of Strings Theory, and use these steps to finally describe its state of the art.
I really like this man, wish I could have attended some of his classes.
you just did!
@@frogz technically one class is not the same as "some" of his classes, I will attend more however, but you are right, I did just attend one .I was actually reminiscing on when I attended collage 46 years ago, wistfully comparing the education we received back then, to the advanced classes like this one that are available in scholastics today. Cheers mate! Thanks for the comment.
wowsers ! .. just watching the equations, and the voice .. is like listening to a symphony ! ... mind engaging !
Thank you Professor Greene for this excellent series as well as The Fabric of the Cosmos !
Thank you for doing this; very kind. By the way, I attended a lecture/book promo of yours in Ann Arbor, MI, many years ago. I still remember your ability to break down complex ideas so that they’re understandable.
Thank you for the history of the development of modern physics. You sure have a gift in translating the technical “silo" language of Math & Physics into a fine novelist’s narrative that is clear and captivatingly inspiring
Professor Greene your explanations during this series always amaze me and thank you for your ability to provide insight into what I am sure is a very complex subject, but in a way that everyone can understand and learn from!
Wow, thank you again, it was amazing.
🤯 every episode is fantastic. Thank you for continuing to give such insight to these concepts! I really appreciate you breaking down the equations and showing how work towards developing an intuition when going through them.
The subtle change in the professor's hair style make him looks even smarter.
He issss smart man!!!!
This series evolves quite impressively and it`s a pleasure to listen to. Just amazing. Keep up the good work.
OMG.. So amazing,today I truly understand beauty of equations...just amazing professor, thanks a lot 😄
Impressive lecture as always. Priceless.
Another Great Video! Thank You.
Very nice video sir
Thank you so much. In this pandemic era I am learning so awsome things. I going back to my early days as an student. I think now I have time to pay attention and understand these concepts. I understand that the universe isn't an explosion, but an expansion. Thank you.
These ideas are indeed very hard to reconcile with, to come at friendly terms with. My mind is a hot dense quark gluon plasma of questions and perplexity right now. Thank you so much once again sir.
ufff, buenísimo, pero que difícil. Gracias Brian.
This video was not 48:25. It just expanded into my brain.
thank you yet again professor, i have nothing to add or ask right now, just thank you
You are great, guy :)
The balloon metaphor is my favorite one in all of physics. The metaphor does not go far enough. The surface of the balloon represents the three D manifold of our spatial dimensions, but the area under the surface represents our PAST. The area the balloon is expanding into is the future. Here, we can actually visualize time as a three aspect spatial dimension. Like a black hole, the information content of the of the universe is a function of it's surface area (The present.) The area outside the balloon which the balloon is expanding into is the higher vacuum of utter nothingness, our FUTURE. The area underneath, the Past, contains nothing but the dark energy which is what is blowing up the balloon. The surface of the balloon is comprised of the Higgs field and either/ or Dark Matter. The fabric of the Dark Matter would super strings of string theory. One caveat of this balloon analogy is that the universe is likely expanding to a minimal surface area. Whatever that minimal surface is, it could lead directly to the big rip once it is reached. Pop goes the weasel.
thank you professor Greene, it's been really an inspiring episode, a journey through beautiful equations giving sense about universe expansion and its infinite density at a point, of origin back in time, of big bang but i didn't get the point of considering, of why, that the scale factor a(t) is being related to certain power law, 't to the power alpha' i mean i didn't get the base reason for such i mean why not the exponential law which equals unity at time zero. or maybe i sound silly to ask such.......well i hope professor i'll be getting the answer soon. Thank you
Basically, because he knows the answer, and doesn't want to waste time going down false trails. As for why not an exponential, we can see that the universe is not expanding exponentially.
I like how u choose ur words carefully in explaining such complex concepts!! I would have used "like" filler a million times to explain it 🤣
Sir that's a brilliant talk, loved it
Brian Greene for President!
yes professor you are right how can be something like infinite density. it is just that the amount of matter and radiation are so huge that it is quite difficult to express in form of numbers.
Amazing video! Thank you
fascinating. Much appreciate it.
Thanks Pr. Greene for this great series. I am facing a paradox with respect to this last one: does the metric of space increase with the space expansion? if I were to measure now the distance between our Milky Way and some Galaxy using say a standard stick the number of those sticks would be the distance. If I were to repeat the experiment some millions of years from now I would need some more sticks because of the expansion of the Universe.... provided the sticks themselves do not expand with the universe. However when you mentioned the density of energy for radiation it depends on 1/a^4 and not 1/a^3 because the radiation itself expands with the universe: does this mean that the measuring stick does expand with the universe? then how come we can measure the space expansion?
I would love to have a one on one with Mr. Greene...I think I could make him see something different.
What?
Question:
Does it take energy for the Universe to expand? If it does, does it mean the expansion will not be infinite? If it does not, does it violates any conservation laws?
conservation of energy doesn't really apply to an expanding universe. Conservation of energy requires a closed system. Expanding universe is not a closed system.
Your question about what energy is driving the universe is exactly what people call dark energy. No one really knows what it is, hence the term dark. If the dark energy were to somehow run out, then the universe expansion could slow down and perhaps stop.
Awsome.
I consider that the boundaries of the universe are determined by the propagation of fields - likewise I believe dark energy/dark matter are in fact regions of space that are perhaps sharing dependencies but not completely attached and as such we are presented with a region of unknowns...
If I attempt to draw just 3 lines that meet at a point; I usually miss -- and end up with some tiny triangle in the center. Hubble's observations (and also modern observations) don't seem sufficiently precise to justify the strong statement that, winding the clock back, everything in the observable universe would meet at a single point.
They don't just eyeball points on a graph to figure out the expansion rate, they use statistical techniques to get that, based on the data and the errors in the data. The result also has an error.
We are told that the date for the birth of the universe is calculated by working back using the speed of expansion now. How do we know that the expansion rate of the universe has always been constant? Can anyone out there help me with this question?
"let's see an example about the whole universe" -----> me, moving towards the monitor even more while putting on the rarely used glasses
I would so Love to have Brunch with you, Mr. Greene.
Hello! When Einstein spoke about the static Universe, it is true... We know periods of expansion, dynamism, but also periods of conservation of energy to give rise to other atomic structures.. Thank you!
Thanks😍😍
The weather is cloudy and rainy here too. 🙃
Great content doesn´t get very many viewers, that´s youtube for you.
The beginning started for me to understand the subject so cooling with real ZEAL to educate not only children but we oldies as well who have dumped all somewhere.
Thanks, Brian!
I brought my son in (10yr) to watch the R connection transform as I thought he would like it. he went and got a Dice and showed me that he noticed that if you start at the six and turn it across 1 down 1 and back to original, then the six dots have turned on there side, then he told me he had noticed this and that he thought it was a non Euclidean plane.. I dont understand what he means but he explained in graph form what is happening. I still dont get it, I cant do maths
I love the rocket science analogy - first yr physics the prof says 'it's not rocket science' I cry - yes it is :(
What would be the phenomena of observation of a non-normalizable probability distribution? Eg: Observations on a Cauchy distributed random variable.
The interior of the barn looks like it was nicely done but the outside needs some tlc
Wonderfull pedagogy, thank you!
I have a question : since (global) curvation arises from the (local) metric, wouldn't a metric depending on a single scale factor (when applied to the entire - isotropic and homogeneous - universe) give rise to a null curvation overall ?
But you said the 3 scenarii (k=0,1,-1) would be compliant with the isotropic and homogeneous hypothesis, so I must miss something ..
I tried to resolve this by realizing a(t) just sets the relative change in distance between any 2 points over time, and this can be applied to an universe which have either k=0, k=1, or k=-1 to begin with. Maybe I'm confused because a metric depending on a single scale factor does not mean having a metric reducing to a simple diagonal matrix or something ...
Thanks Prof, I enjoy your daily equation. I am trying to reconcile this idea regarding the universe being infinite. If the universe is considered to be infinite, then how could it be explained that it is expanding? How can infinity be added to?
That's the power of infinity. Infinity can always be getting bigger and it's still infinity. And infinity can get smaller and it's still infinity.
Its expanding only in the sense that the space at every given point is expanding, but in an infinite universe the boundary that contains it would not be expanding because this boundary would not exist.
If galaxies that are 'far away' (a long time ago) look like their speeding up... wouldn't that mean that they were going faster previously, and therefore it's possible that they are no longer going at that speed? And could in fact the universe be compressing, but the compression of light just hasn't reached us yet? My brain hurts.
Q: If there is a redshift of light in the universe because of distance,
then galaxies that move away with constant velocity seem to move away with acceleration.
If so, the bigbang-theory is possibly wrong?
thanks
Can it be possible that when a star's core has enough energy that it smashes the particles at such energies as that before the higgs field turned ON, (then according to the same theory) the particles were massless, all 4 forces were unified and therefore the star collapses to make a black hole. Thus, light cannot escape from the black hole as the forces are combined, and light is overpowered. This also verifies that most black holes need to have a high mass, density in order to cater to the energy needs.
And because the higgs field is the PROBABLE reason for asymmetry between particles and anti particles, with the higgs field off, there is perfect symmetry, the particles annihilate each other, leaving nothing detectable with the STRONG unified forces on top. And because all the mass, particles have been converted to energy, energy bends spacetime, therefore we experience a "gravitational" pull. Classical physics does not account for a unified force and thus our physics breaks down at the blackhole.
Watching from Ireland 😊
_The universe itself keeps on expanding and expanding_
_In all of the directions it can whizz_
_As fast as it can go, at the speed of light, you know,_
_Twelve million miles a minute, and that's the fastest speed there is._
_So remember, when you're feeling very small and insecure,_
_How amazingly unlikely is your birth,_
_And pray that there's intelligent life somewhere up in space,_
_'Cause there's bugger all down here on Earth._
With my no education and very limited intellect, it's no wonder that reading explanations of the cosmos gives me headaches. My question is this, if the universe is expanding, things are moving away from things at terrific speeds, then what we see is no longer where it was light years ago. So, are all objects currently in a different direction from where we now visualize them, either to the right or left or up or down, or are they in the same place only further away?
Thank u sir u made my day.
Some dude comes up with these equations and I’m just having a hard time comprehending the concept
Are experiments occurring to understand better spacetime, such as using the Casimir effect?
IF we shrink all matter, compress to fit that infinitesimal size, would all the known mass/things in the universe fit in that "point"? I always imagine that shrinking all the universe to a singularity would not be a infinitesimal point, but something that would be visible because all that there is would not "fit" in a point. Are there calculations like that?
Initial mass is assumed to be something like planck mass, initial size of the universe something like planck length, and so on. Then somehow during inflation the rest grew out of nothing... you can see from my explanation that I am also still learning. And I am more and more convinced that this question still is not answered finally.
Where we are it would be really really dense. But there are still places that infinitely far away that are also very very dense. At least in an infinite universe. And people tend to think it is indeed infinite in extent.
We need a theory of quantum gravity to answer those questions. That's one of the problems with relativity, it breaks down when you smash things really close together. And quantum mechanics doesn't explain it very well either because it doesn't include gravity.
All we can say is that at a previous time the universe was in a more dense state than it is now. What that ultimate density would be like nobody really knows. Our equations break down into infinity at that point, so in less infinity is real, which most physicists don't like, we just don't know.
You caught my attention, and I want to watch a few more of your UA-cam videos.
I hope someone can explain a few things to me. I’m not sure if that will be you. I like the thought that things have purpose that we have what we have, and they are there for a purpose. Otherwise, there is no purpose.
I have many questions about black holes:
What is the Natural purpose of black holes? Why do they exist? If they existed for such a long time wouldn’t they have gobbled everything up? Have we ever seen evidence of a black hole exploding as if it were creating a new big bang?
LOL at 33:09. Love it!
It all starts nice and smooth...all of a sudden: complex maths, solving differential equations, introducing alfas out of nowhere...I lost you!
This does not make sense. The expansion of the universe is faster the further away from us, as demonstrated by the balloon: from our spot, going from 1 unit away now is 2 units away; however, if the point of view is at the opposite end of the balloon, would triple distance away. Seems it all depends from our point of observation.
I don't see where the triple away part comes from. You're not seeing the analogy correctly. No matter where you are on the balloon, everything expands away from you at an ever expanding rate.
Personally I wish people wouldn't use the balloon analogy. Because balloons are three-dimensional and that misses people out. It's easier to see just on a flat sheet that stretches out and expands. It makes more sense that way. there's lots of good videos that demonstrate how there is no center to the expansion. You can look some of those up.
@@dankuchar6821 I agree a flat rubber surface as our universe is flat would be a better analogy than a balloon. However, the Hubble constant is a constant expansion of the universe that increases the farther away from us. This I do not understand if it is constant. So, it must be some optical illusion. As it is 3 units away from us, in the balloon analogy, and doubles in expansion to 6 units away. So, one unit away from us will now be twice away. Constant expansion of doubling. This will give us the red shift which is an actual physical observation. We do not see "space fabric" itself expanding. What makes more sense to me is that space does not expand, but all galaxies are being pushed at the same Hubble constant.
The problem with the baloon example is that the "galaxies" ( purple squares in the example baloon) also grow in the same proportion in relation to everything else, so to them, the distances are all the same. It works to someone siting outside, but it is not the case to them. Or us, if we were on the "baloon".
I agree. The balloon analogy is not a very good one. There are better examples.
Prof. Greene needs to paint his house 😄
i loved this
Thanx brian for the info and the place to share ideas. - At time 9:00 there is a hubbles diagram that show how supernovas follow a pattern as how they are expandding but Brian needs to say that at the right up corner at the end stars no longer stand in such patters anlist that is what the phd says in the video: THE MISTERY OF DARK ENERGY THE VON CARMA LECTURE SERIES 2008 at time 20:13 more resent supernovas picture, he says that; take a look to the north right side and notice how the system in which the supernovas are found make un up curve kind of the system opens almost from the bigening from the center to the right top side, the north side is the one that always opens the most in all systems as well our sun has the corona on top north side, is been noticed that at our suns corona gases and matter speeds up when just lieving the suns electromagnetism at the suns corona so my guess is that such speed up of wind speeds cause it leaves the sun that is at much grate presure than out the sun sphere. Same thing happens to the supernovas that at the point of leaving the system where they hapen to be the stars are much more seperate cause they are stars of a different level so those stars no longger fit hubbles constant.
I am a big fan of BG
the shape of the universe is determined by the field content (I believe)
I found out that the time reversal dosen't exactly reverses the path same as it was before for eg in three body problem then how can you conclude that the bigbang happened by reversing the time? (The same mathematical equations that gives you the path in future dosent give you the position of it it ln the past.)
You assume a(t) = t^α. What if a(t) does not follow a power law? would we reach the same conclusion?
What if the balloon analogy was wrong? It doesn't well capture the expansion as the entire universe isn't a plane. Implication is misconstruing of derivatives. What if everything in the universe is contracting at the speed of expansion creating the illusion of an expanding universe. It would mean our universe is actually static (as the size of the universe is constant including the boundary of the universe) but appears to create the illusion of expansion due to the contraction of everything. This causes the flow time. Opposition to the contraction causes gravity.
Photon is the only particle that does not oppose the contraction theory, that is why it moves at such speed, forms a constant in the universe and appears to be massless.
I can’t thank you enough for doing this🙄
How is the cooling of the expanding universe explained?
e.g. - Imaging a single particle moving at a speed v, (which is kT); what causes it to reduce it velocity?
As space expands, the wavelength of energy stretches with the expansion of space. A longer wavelength is lower energy effectively cooling the universe. So the wavelength of light expands with the universe, Even though light always moves at a constant velocity that never changes.
A particle moving through space would appear to slow down as space expands around it.
Those are some simple analogies, I hope they help.
If you divide infinity by infinity you get one. Sorry just thought I would throw that in there. That has always bothered me. Limits right?
God called me to throw in some creationist math.
If it's nowhere to expand for the universe and all the matter that universe needs to expand to is used or gone. What would be left, where universe can expand to???
You say the universe doesn't have a center, but if you were to rewind the motion of all the galaxies, they would eventually reach a point, that really does exist right now and that is located in our universe, wouldn't you?
I can imagine the events between 5:00 and 7:30 via Twitter, Facebook or Instagram 😂📲
If one were to take a skeptic approach and say that hubble redshift might arise from other unknown phenomenon, what is the tertiary evidence for expansion?
It's called a distance ladder. Before you get to red shift there are other methods of measuring distances in the universe, such as parallax and then variable stars etc. Red shift is the farthest rung on the ladder.
Also one must come up with another reason for red shift. And there's no known physics that can cause photons to stretch in wavelength and lose energy except for the expansion of spacetime.
There are some hypotheses, but there is little to no supporting evidence. While there are multiple levels of evidence for the expansion of the universe.
The apparent speed of distant galaxies rushing away from earth's perspective is as old as the photon travel time. Wouldn't it be more correct to say "The further the light source from the earth the faster the source of emission 'was' traveling away." (Rather than the commonly used present tense "is") Since a galaxy emitting light at 10 billion light years distant, will take 10 billion years to reach the earth for us to observe its current speed signature?
yeah i was right there when big bang happened, it was amazing, africa came out first, then other continents, all planets formed round except earth, earth emerged out flat tray shaped that's why we have life on earth,
what if only the 5% is accelerating , the other is a deeper constant with its own space/time
im 13 years but still i understand universe same like u
Where does "Einstein's Constant" play into the theory of the expanding universe? Didn't Einstein make up that number so that the general theory of relativity would be consistent with a static universe and then discard it when Hubble proved the universe was expanding? And wasn't that constant revived 70 years later to explain the amount of dark energy in the universe? I'd bee curious to learn about the role of the constant in our understanding of the universe. Thanks...
If all is moving away from each other, how do galaxies collide?
Because, while expansion is important on large scales, on small scales (such as a galaxy cluster) expansion is overcome by gravity.
20:55, Calligrapher or Physicist?😁
When we think of a sphere, it has an intrinsic geometry, and can be viewed as a 2-dim object in 3-space, and the boundary of a solid ball. In the balloon metaphor of the expanding universe (as the surface of the balloon) ... this sphere/balloon is not the boundary of anything?
In the balloon analogy, there is not a boundary. It's a two-dimensional analogy of an expanding three-dimensional space. A famous three dimensional analogy is raisins in bread. As the bread expands while the dough rises in three dimensions the raisins get further apart from each other. The raisins would be analogous with galaxies in the universe.