What Are the Key Questions and Challenges in Understanding Quantum Gravity?

[SephQ]

TL;DR

I recently watched a video on Quantum Gravity, and had a few questions.

Disclaimer: I’m new to QM, so things I say might be wrong, please forgive me for possible inaccurate info.

So as for what I know, quantum gravity is the study of merging GR and QM on gravity.
Here’s a few questions I’m interested about on the quantisation of gravity:
String theory
1. What is a graviton in string theory?
2. Why do these 1d vibrating strings exist in a 10d plane such that it somehow bends spacetime?
3. Why is it not really considered to quantize gravity nowadays?
Loop Quantum theory
1. How does spacetime exist as loops?
2. How do you find out the mechanics of space time in a quantum scale?
3. In one of the formulas, it shows that higher energy rays travel in a quicker speed, but in experiments it doesn’t really show so.
(a) Is it possible to work with low energy rays?
(b) Could there be something missing in the formula?
(c) It sounds a bit similar to how light works under refraction, is there any correlation?

Sorry if I asked too much, but that’s about it. Feel free to comment anything you think is right! I’ll come back occasionally to check.
Cave Diving into QM surely did explode my brain, haha.

Best Regards,
Seph

 

[PeterDonis]

I recently watched a video on Quantum Gravity

Please give a specific reference. And please be prepared to be told, once you have done so, that the video you watched is pop science and is not a reliable source. There's a reason why we recommend textbooks and peer-reviewed papers here at PF.

 

[SephQ]

Please give a specific reference. And please be prepared to be told, once you have done so, that the video you watched is pop science and is not a reliable source. There's a reason why we recommend textbooks and peer-reviewed papers here at PF.

The link is below this thread!

Since you said about textbooks, do you have any recommendations I can read as a beginner? It would be really helpful.

Best Regards,
Seph :)

Youtube video

 

[PeterDonis]

Since you said about textbooks, do you have any recommendations I can read as a beginner?

Quantum gravity is not a beginner's topic. Any textbook about it will assume that you already have a graduate level knowledge of both quantum field theory and General Relativity.

 

[PeterDonis]

The link is below this thread!

And indeed it is a pop science video. It's a pretty good one as such videos go, but it's still pop science.

 

[PeterDonis]

Sorry if I asked too much

For one thread, yes. Each individual question you're asking could be a thread all by itself--but before even asking questions, you really need a better reference as a basis for discussion. So you need to work on finding better references as a starting point. Yes, I know I said there aren't any beginner level references on quantum gravity; but that doesn't change the fact that you need better references to have a PF discussion of this topic. There just aren't any beginner-level answers.

A big part of the reason for that is that we don't have a good, accepted theory of quantum gravity that's been tested by experiment. It's an open area of research. That means that pretty much anything you read about quantum gravity is not describing an experimentally tested theory; it's describing somebody's hypothesis about what might eventually turn out to be a workable theory. Asking "why" questions about such things is pointless: nobody knows why, it's just a hypothesis that we currently have no way to test.

A final note: threads about this topic belong in the Beyond the Standard Models forum.

This thread is closed.