Introduction to Loop Quantum Gravity - Lecture 1: The empirical basis of quantum gravity
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- Опубліковано 26 лют 2018
- This course was given at the CPT in Marseille in February and March 2018. Lecture 1 is on the empirical information on which the theory is based.
A latex transcript of the lectures is available here: arxiv.org/abs/2305.12215
(thanks to Pietropaolo Frisoni) - Наука та технологія
Starts at 4:17
Thank you
Always good to hear from you Mr Carlo Rovelli
I've been listening the book "Reality is not what it seems" several times to understand it better and better. No I thought about looking for a video on UA-cam about the topic, found this one, listend to the prof thinking it would be an arbitrary person and then suddenly realized that it is the author of THAT book. Really interesting to see him in action.
Great and exciting work! Loved your two books as well: Seven Brief Lessons on Physics and more recently Reality Is Not What It Seems: The Journey to Quantum Gravity. Both excellent reads for a layperson like myself. Can't wait to read your latest: The Order Of Time!
Fascinating lecture. Love Professor Rovelli.
All thanks to Prof. Carlo Rovelli for everything he's done.
@carlo rovelli Do you occasionally read email?
@@analyse3306 Gravity AND ELECTROMAGNETISM/energy are linked AND BALANCED opposites, AS E=mc2 is F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. Gravity/acceleration involves BALANCED inertia/INERTIAL RESISTANCE, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. A PHOTON may be placed at the center of what is the Sun (as A POINT, of course), AS the reduction of SPACE is offset by (or BALANCED with) the speed of light (c); AS E=MC2 IS F=MA; AS ELECTROMAGNETISM/energy is gravity. The stars AND PLANETS are POINTS in the night sky. The ultimate unification of physics/physical experience combines, BALANCES, AND INCLUDES opposites. E=mc2 IS F=ma. This necessarily represents, INVOLVES, AND DESCRIBES what is possible/potential AND actual IN BALANCE. Gravity IS ELECTROMAGNETISM/energy. GREAT !!! GRAVITATIONAL force/ENERGY IS proportional to (or BALANCED with/AS) inertia/INERTIAL RESISTANCE, AS ELECTROMAGNETISM/energy is gravity; AS E=mc2 is F=ma IN BALANCE. BALANCE and completeness go hand in hand. It ALL CLEARLY makes perfect sense.
By Frank DiMeglio
Exciting theory indeed
Dr Rovelli is lecturing me on LQG. Awesome.
@carlo rovelli If I want to learn loop quantum gravity I need to know previously QFT or just non-relativistic quantum mechanics & general relativity?
Best regards from Brazil!!
Many thanks to prof. Rovelli and Francesca Vidotto for sharing the course videos. BTW, the book (Covariant Loop Quantum Gravity) is awesome.
How do we construct a theory of quantum gravity? What do we know? What are the experiments we already have? What support the belief in one direction of research rather than another? This is a very general discussion, no maths involved, enjoyable also for the general public, recommended to philosophers. (Audio is not perfect, it is fixed from Lecture 3.)
Francesca Vidotto quantising gravity is too tedious . but if quantum mechanics "is" GR by the ER=EPR we have a breakthrough!
Most of your questions are extremely well answered in his book "Reality is not what it seems".
Also he's published several technical books on the subject if you want maths. Even his public books contain some maths and extremely complex ideas which depend on your grasp of current well proved complex scientific theories.
Further more Faraday and Einstien were both not so maths orientated and both play arguably two of the biggest roles in shaping science today. Rest assured through this is scientific theory and as such is based on well proven science rather that what the public thinks of as theory which is a bit more like guessing.
Thank you for the book!! Greetings from Paraguay!
Well first I guess you have to believe tha "space is bent" crap. I usually stop there, but I gotta give credit to LQG for making way less baseless assumptions than string theory.
The cloud of possibilities which might manifest as myself will try a bit of communication here. IT FROM BIT. Reading and trying to understand one of the prof's books has unbelievably blew my mind, mostly as a result of the impact of the expressed need of a new way of thinking about space and time if we are about to reconcile general rel'y and qm. As already hinted at the beginning of my post, maybe if we are to prove the quantum nature of space we need to start refering to ourselves as objects which follow some or all qm' laws. It from bit. Cheers.
I love how he assails string theory without calling it by name
LQG is a "way of looking", if you already see how it is an aspect of relative timing connection rates in coordinated conics, then the details of the Mathematical derivation in reciprocals of the Holographic Principle are "ready to prove" theoretically.
It's all just a "way of looking at it" in all honesty. A fellow named Donald Hoffman kind of goes into this in his view of reality where he is starting from first principles and looking towards consciousness itself in an attempt to explain space time and while on the surface it sort of sounds kooky when you really get into it you realize it is nothing of the sorts and may very well be the true nature of what is around us. Our maths are simply just models used to represent the world we see around us but everytime we get down to the base we hit a wall when we reach a point where math fails every single time. In our current understanding it starts to fall apart the minute the observer is added to the system. We reconcile this using super position and uncertainty principles but in reality those are simply just mathematical models used to explain the fact we simply can not know if we are not looking at the system in some way. Starting with the observer and working backwards has definite advantages.
When we combine his work with that of Susskinds and consider the holographic principle it, to me anyway, starts to become apparent that Hoffman is explaining humans observations of a sea of 4 dimensional wave forms on the surface of the universes edge as we can project the entire universe onto the 2D surface on the outside of the universe and us being inside observe such waveforms as time and space. Despite these simply being constructs of our mind designed to interact with these waveforms in some meaningful way. We are just one of the waveforms.
All thanks to Prof. Carlo Rovelli
The set of scientists who say we know things for a fact are the scientists and the set of scientists who make revolutionary discoveries are mutually exclusive
Matter is quantized.
Because photons are quanta.
And matter is photons trapped over their own gravity.
Because Eo Uo
Space has characteristics. Qualities.
But Nettleton decay cosmology provides the topology for loop gravity.
A homeostatic universe maintained by the reciprocal processes of electron capture at event horizons and free neutron decay in deep voids.
The connection is exactly through this neutron passage. As if a neutron sits right on the event horizon connecting the maxima to the minima. One one side is electron capture. The moment the electron rejoins the positron to make a double cover of the Higgs.
And on the other side of event horizons, in deep voids, a free neutron is decaying. The electron is ejected creating a radial field with Coulomb pressure.
DM is decayed Neutrons
DE is the expansion caused by that decay from 0.6fm³ neutron to 1m³ amorphous monatomic hydrogen gas. A volume increase of 10⁴⁵.
A lot of videos/lectures about LQG include this particular statement that this is not aiming to be a theory of everything.
My brief reading on thermodynamics would not put thermodynamics in the category {QM, GR, SM}. Quantum thermodynamics appears to violate classical thermodynamics, and also have non-consistent laws when translating standard thermodynamic laws across to the quantum regime. I would say this is due to the fact classical thermodynamics was empirically derived, which has it's detriments. However, I am not up-to-date with the latest advancements and discoveries.
what are the prerequisites for this course ?
Just follow it until you get stuck, then pick up the pieces you miss. It's timeless. Prerequisites are a general interest in a different view of reality.
What are the evidence found that push physicists to quantize gravitation ? Apart from formalism, what necessity ?
thank you. The granularity of space is a long neglected idea. Am I understanding the idea of LQG correctly by saying that 'space is a collection of very small cells wherein matter resides'? If so, can we explain gravity as the asymmetric distribution of these cells? Small jumps of matter from one cell(or one ensemble of cells) to the next would be random. But if the cells were more 'closely packed together on one side', then matter would more likely jump that way because there are more opportunities to go that way. The use of quantized space also allows a simpler understanding of the phrase 'the curvature of space' - curvature could be understood in the same way we read a topographical map - where the lines of curvature closer to a massive body represent an increasing 'concentration' of cells. And the vibration of these cells are EM waves? And the region between these cells (where there is no 'space') is where dark matter resides(because it is something with mass but no dimension and only interacts with gravity)?
I could never visualize the concept of field theory- where doing something over HERE has an effect over THERE, with nothing in between. But the idea of 'quantized space' gives my weak brain a better framework. Consider two black holes very close to each other. At the Lagrange L1 point their gravities should cancel out. So light passing between these bodies should be unaffected. There should be a clear zone between them. But if space were quantized, and the massive black holes were stretching space, then the light between them should dim greatly-because there are simply fewer cells to transmit the light. As a poor analogy to the decreased transmission of sound in rarified air.
Books name?
Very nice talk, looking forward to watch the next lectures...
Unfortunateky, it looks like we're going to need some fancy theory to solve the conundrum.
And of course, we'll gonna need to understand the underpinnings of both QM and gravity. Without that, no real progress is expected
Does someone have the link to the Dropbox?
You can find the mentioned Dropbox link in this page: www.cpt.univ-mrs.fr/~rovelli/
24:17 The frequency of the light won't change, the wavelength and its velocity through the crystal will. I know this sounds wrong, but the index of refraction is the ratio of the speed of light to the speed of the light in the medium. Light slows down because it interacts with the atoms of the crystal, and the interaction of the vertical component of the electric field of the light (Maxwell's 3rd and 4th equations). The wavelength and the speed of the light changes, the frequency won't. if it did, the speed of light in the crystal would be the same as its speed in a vacuum, because the change in wavelength would be counterbalanced by the opposite change in frequency, making the speed of light the same in a vacuum and through the crystal.
If this is true wouldn't it mean that pie is finite but we just haven't found the end
How do you reconcile Loop Quantum Gravity with big bang expansion?
is it OK to say "bullshit" in an academic circle? just wondering.
"Science is about adding knowledge and reinterpreting previous knowledge, it's not about discarding previous knowledge." This is very vague. Does not "reinterpreting" allow for effective discarding of previous "knowledge"/understanding, such as in the example of Einstein reinterpreting ideas of space and time? Sure, Lorentz invariance is still unbroken at ordinary scales, but what is your argument for it still being so at the Planck scale? Without experimental insight, all these arguments are ultimately tied to personal whimsy.
I’m listening , amuse me
I don't think Popper was trying to say that scientists do not use inductive reasoning to gain confidence in a theory. But gaining confidence in a theory is not the same as proving a theory correct.
Falsification was not presented as a working methodology for scientists to use to do their work. The idea that a theory has to be, in principle, falsifiable is part of Popper's answer to the "demarcation problem", i.e., what distinguishes science from pseudo-science.
In any case, sometimes you do not know whether a theory is incorrect, or that an experiment that seems to contradict theory is correct. I think Steven Weinberg, in his book Dreams of a Final Theory, archly observed "no experiment should be accepted unless it agrees with theory!" He was making a humorous point, I think, but one with some truth to it.
Selon Carlo Rovelli, au-delà de la réalité y compris nous-même , il n'y a rien ! Selon le génial Robert Openheimer , le vide est l'enclos du soleil. Le soleil c'est déjà quelque chose. Carlo refait tes devoirs !
Ohhhh shit, C-Ro be clowning on string theory! Shots fired, nugguhs
Why loops? Why not spheres? Action spheres? They expand from a point, at the speed of light. Their surface area is the present. Their volume contains history.
@8:00 dark matter? Wasn't he around in the 1970's? It's the right-handed neutrino. Definitive masses for the light neutrinos is not fully in yet, but I'd bet a million dollars if I had 1.1 million to play with on ν_R. You should also be clear about whether spacetime itself is discrete (not a smooth manifold) or whether it is rather just all local non-trivial topology. LQG folks seem allergic to closed timelike curves, so they go ostrich mode. But if you admit Planck scale closed timelike curves on a smooth spacetime, you get quantum mechanics out of it, with no further postulates.
Oh Ravioli! Oh dear Ravioli!
Context, summarizing main results and how a theory compares to others in its class is really important as a motivation, but it’s also quite frustrating as an introduction.
I just had to skim through an hour of lecture and I’ve come no closer to knowing how loop quantum gravity works.
If it takes 10 lectures or a semester or a PhD to master the topic, that’s fine, but in that case let’s actually get to work learning how to crank the theory.
The place where it makes sense to compare a theory to the state of the evidence is when you understand it well.
(Though I repeat that it’s good to start with some broad brush context, summary and overview, it’s just frustrating if you’d like to get to the point of understanding this particular theory.)
05:35 My hope is to see verified predictions to be tested before umm ummmmmmm...... before dying :D
carlo rovelli I might just l, if it’s meant for laymen. Gotta finish Lee Smolin’s “The trouble with physics” first :)
Which I forgot on the plane yesterday.. Damn :/
From the real Carlo: the comment above is from a fake account impersonating me...
So the empirical basis for loop quantum gravity were several null results? That is a woefully bad basis for his highly speculative theories. Especially considering it was loop quantum gravity that made the wrong predictions of Lorentz violation, which were BOTH points 1 and 3 (although he seemed confused about the fact that point 1 is also Lorentz violation, which he put separately as number 3).
LQG is not really a theory. Its closer to a concept
@@ntf5211 I don't think you said anything meaningful
Hahahaha 😂😂😂😂😂😂😂😂😂😂😂😂
What's the physics theory that explains the utter douche-i-ness of the guy in the front of the class who looks back toward the camera in the beginning?