Loop Quantum Gravity Explained

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It’s time we talked about loop quantum gravity. What exactly is it? What are the loops? And can it really defeat string theory in our quest for a Theory of Everything?

Hosted by Matt O'Dowd
Written by Graeme Gossel & Matt O'Dowd
Graphics by Leonardo Scholzer
Directed by: Andrew Kornhaber
Executive Producers: Eric Brown & Andrew Kornhaber

The holy grail of physics is to connect our understanding of the tiny scales of atoms and subatomic particles with that of the vast scales of planets, galaxies, and the entire universe. To connect quantum physics with Einstein’s general theory of relativity. Our search for a theory of quantum gravity is a century old, and we’ve talked quite a bit about it already, including what’s probably the lead contender - string theory. But string theory isn’t the only game in town - or so some physicists believe. There may be another way to reconcile the physics of the tiny and the gigantic - another way to a theory of quantum gravity that avoids a lot of conceptual baggage like tiny wiggling strings made of coiled up extra dimensions. That other way would be loop quantum gravity, and today we’re going to learn exactly what it is.

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[emanuelebonura]

"just quickly, let's review all of quantum mechanics" LOL

[listenatwork]

"Let's review all of quantum mechanics."

"Actually, quantum mechanics forbids this."

[WylliamJudd]

"Loop quantum gravity tries to quantize general relativity, with no strings attached." I see what you did there!

[AjinkyaNaikksp]

9:07 - For everyone wanting to learn more about the topic - "Quantum Gravity" I suggest reading these two books - "Three Roads to Quantum Gravity" by Lee Smolin and "Reality is not what it seems" by Carlo Rovelli. They are masterpieces especially the one written by Carlo Rovelli really gives you a great insight into this topic.

[marcusbenjilake]

"A seriously loopy space-time, with no strings attached."

[matthewwhite]

I'm going to need this explained again... much slower... with finger puppets.

[OnlyARide]

"Bröther may I have some quantum lööps?"
-Schrödinger's cat, shortly before death (maybe)

[Ineedhelpig]

"With no *strings* attached.".


Hands down one of the best puns ever.

[dreammfyre]

I feel like a dog watching humans talk.

[DeathbyPixels]

Me: Oh boy, I am tired. Today was really exhausting.
PBS Space Time: Loop Quantum Gravity Explained
Me: Yes I definitely have the energy for this.

EDIT: Okay, I actually did get a bit of a hold on this concept. I definitely need to start watching more of your videos to truly be caught up, but I cannot express how grateful I am for you guys to be making all these ideas approachable for people like me. It’s a gift.

[henrycgs]

I find it fascinating how deep we're going. It's going to get to a point where it's meaningless to talk about spacetime, mass, charge and other familiar concepts to us, and it's going to be purely abstract exchange and evolution of data. It's like Sims finding out they're made out of bytes.

[andretheron]

"So quickly, let's review all of quantum mechanics"
Sounds like the last math class before an exam...

[aghosh]

Masterpiece of physics presentation.
For any budding physics geeks 16 year old, this is a treasure.

[thekaboominator]

This is beautifully explained - I'm a physics student, finishing up my fourth year at uni, and even with having studied Quantum Field Theory and General Relativity, I find string theory and LQG almost unapproachable to understand. Most explanations I've found tend to get buried in the maths without every really explaining the idea of the theory itself . This, however, succinctly explained both the motivation and idea behind the theory in a simple manner. Thank you very much!

[Crybaby_Club]

Me: oh look a new PBS Space time video, and the title sounds so interesting!
2 minutes into the video: I have no idea what is being discussed here and I think my brain is oozing out of my ear

[thepoofster]

If space is actually a 'pixel grid' of loops, and space is expanding, does this mean that the loops themselves are expanding? Or are the loops 1 dimensional and therefore cannot expand.

I would assume if they have constant size like the planke length, there are more loops being created as expansion occurs.

I know common sense doesnt work at this scale so any help would be appreciated! Ty!

[photinodecay]

I understand literally every other video you've done, but this space of loops sends me for a loop in space.

[billdooder]

It must be weird being that guys kid, "son, it's time we had a talk about loop quantum gravity"

[pattsw]

'Not true, damn..."

Very nice. Took me a second. It was so good that if it hadn't have been for the preceding puns, I would have definitely missed it.

[goatmeal]

"How to talk to your kids about loop quantum gravity"