Loop Quantum Gravity Explained

PBS Member Stations rely on viewers like you. To support your local station, go to: to.pbs.org/DonateSPACE
↓ More info below ↓
Sign Up on Patreon to get access to the Space Time Discord!
/ pbsspacetime
Check out the Space Time Merch Store
pbsspacetime.com/
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
End Credits Music by J.R.S. Schattenberg: / @jrsschattenberg
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.
Special Thanks to Our Patreon Supporters
Big Bang Supporters:
David Barnholdt
David Boyer
David Nicklas
Fabrice Eap
Juan Benet
matt miller
Morgan Hough
Quasar:
Mark Heising
Mark Rosenthal
Vinnie Falco
Hypernova:
chuck zegar
Danton Spivey
Donal Botkin
Edmund Fokschaner
Hank S
joe pearce
John Hofmann
John R. Slavik
Jordan Young
Joseph Salomone
Mathew
Matthew O'Connor
Syed Ansar
Gamma Ray Burst:
A G
Adrien Molyneux
AlecZero
Andreas Nautsch
Bradley Jenkins
Brandon labonte
Brian
Dan Warren
Daniel Lyons
David Bethala
DFaulk
Frederic Simon
Geoffrey Short
Graydon Goss
Greg Smith
James Flowers
John Funai
John Griffith
John Michael Kerr
John Pollock
John Robinson
Jonathan Nesfeder
Joseph Dillman
Josh Thomas
Kevin Lee
Kevin Warne
Kyle Hofer
Malte Ubl
Nick Virtue
Nick Wright
Paul Rose
Scott Gossett
Sean Warniaha
Tim Stephani
Tonyface
Yurii Konovaliuk

[@emanuelebonura783]

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

[@RobertKaucher]

Indeed!

[@RumoredAtmos]

I laughed at that too

[@meleardil]

Well... he did...

[@Seeyeay]

It was actually really well done, seemed to piece together other concepts that I had learnt separately in previous videos.

[@emanuelebonura783]

No doubt my man here delivered a solid and concise explanation (like always, I freaking love this channel), but I lolled so hard nevertheless

[@listenatwork99]

"Let's review all of quantum mechanics." "Actually, quantum mechanics forbids this."

[@liggerstuxin1]

listenatwork99 👏

[@moosemaimer]

you can either know all the equations, or which ones are correct, but not both

[@LuisAldamiz]

QM is uncertain about this, mind you.

[@paulmichaelfreedman8334]

And even then your answer is not 100% correct ;)

[@JF-go7gc]

@@moosemaimer they are all correct....just depends on which reality you perceive and work them out from

[@dreammfyre]

I feel like a dog watching humans talk.

[@darkmath100]

LOL

[@sefyboy7183]

@C R Stop talking, you social brick.

[@Mandeepd13]

acuurate af!

[@kinngrimm]

I wonder if dogs can do as we do when we anthropomorphize them.

[@glarynth]

A dog named Spacetime.

[@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.

[@ramsesabreu1870]

Yeah, Carlo Rovelli makes a clear, concise mention of Quantum Gravity in "The Order of Time".

[@DanaNourie]

Ajinkya Naik a great book!

[@shaunhumphreys6714]

@@ramsesabreu1870 yes i concur-carlo rovelli also teaches the philosophy of science so you get quotes from classical greek and roman philosophers in his books, and declaring stuff like love more than the sum of its quantum parts. i dont like lee smolin as he is a time denier.

[@shaunhumphreys6714]

carlo rovelli should be the first one to consult-he marries theoretical physics and philosophy in a wonderfully intuitive way. he is an intuitive physicist, however loop quantum gravity is a weak theory, very contrived. electromagnetic, strong and weak nuclear force were quantised fast and easily and with incredibly accuracy. gravity cannot be quantised.it refuses to be. it has resisted every attempt. noone is anywhere near. because gravity is not a force, it is rather the effect of mass in changing the geometry of the spacetime itself. it's a geodesic. which is spacetime itself, so it doesn't involve any particles mediating a force like gluons, w and z bosons and photons. and for relativistic lorentz transformations to hold, space and time must be continuous, not discrete. otherwise they relativty is violated. the universe may be quantum, without everything being discrete. i had dismissed string theory for a long time, but it is far more likely than loop quantum gravity, and is a complete framework, that answers the suggestions of either higher dimensions in physics, or holographic principle suggested by blackholes.

[@janouglaeser8049]

@@kabirmunjal9149 I'm sorry, I'll stick being team Thiemann 😝

[@WylliamJudd]

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

[@peachybeck]

should be called “no strings attached theory” lmao

[@_sayan_roy_]

That was pretty obvious though

[@seancanning6743]

Well if its in the box it ain't brand new. Try on hauls. Haha

[@raysubject]

most epic comment on any PBS video ever... almost died by laughing... yeah, i feel that way all the time :-))))

[@chicxulub2947]

blasphemy

[@andretheron1833]

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

[@frankdimeglio8216]

Invisible AND VISIBLE SPACE in fundamental equilibrium and BALANCE IS E=MC2 AS F=ma, AS ELECTROMAGNETISM/energy is gravity. Indeed, the ultimate mathematical unification (AND UNDERSTANDING) of physics/physical experience combines, BALANCES, AND INCLUDES opposites. (Very importantly, outer "space" involves full inertia; AND it is fully invisible AND black.) WHY AND HOW ELECTROMAGNETISM/energy is gravity, AS E=MC2 IS NECESSARILY F=MA: TIME DILATION ULTIMATELY proves ON BALANCE that E=mC2 IS F=ma, AS ELECTROMAGNETISM/energy is gravity. INDEED, TIME is NECESSARILY possible/potential AND actual IN BALANCE; AS E=mc2 is F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. Gravity IS ELECTROMAGNETISM/energy. E=mc2 is F=ma. This NECESSARILY represents, INVOLVES, AND DESCRIBES what is possible/potential AND actual IN BALANCE, AS ELECTROMAGNETISM/energy is gravity. The stars AND PLANETS are POINTS in the night sky, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. (Energy has/involves GRAVITY, AND ENERGY has/involves inertia/INERTIAL RESISTANCE.) Very importantly, outer "space" involves full inertia; AND it is fully invisible AND black. BALANCE AND completeness go hand in hand. It ALL CLEARLY makes perfect sense. Great !!! Gravitational force/ENERGY IS proportional to (or BALANCED with/as) inertia/INERTIAL RESISTANCE, 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. "Mass"/ENERGY IS GRAVITY. ELECTROMAGNETISM/energy is gravity. The Earth AND the Sun are CLEARLY E=MC2 and F=ma IN BALANCE, AS ELECTROMAGNETISM/energy is gravity. The stars AND PLANETS are POINTS in the night sky. GREAT !! By Frank DiMeglio

[@ikilledaman]

@@frankdimeglio8216 That is all nonsense

[@NecDraws]

@@frankdimeglio8216 ahm... nope..

[@joshyoung1440]

@@NecDraws lol do you happen to remember what he said?

[@Ineedhelpig1082]

"With no *strings* attached.". Hands down one of the best puns ever.

[@OnlyARide]

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

[@liianhaalea1088]

Underrated comment. Fabulous.

[@nicolasribeiro7914]

this is absolute gold

[@whythelongface64]

It's still funny. I'm from 2021.

[@jorikito]

Can confirm, it's still funny in 2021

[@matthewobrien4745]

Can also confirm for 2021: Ts bussin in humor respectfully

[@TheExoplanetsChannel]

*Best. Host. Ever.*

[@MirorR3fl3ction]

Matt is easily one of my favourite hosts on KZbin, but I mean Gabe was pretty cool too, plus he was the one who managed to explain the basics of General Relativity to me back in those early videos. I think it'd be cool if Gabe came back to co-host once with Matt

[@enterprisesoftwarearchitect]

Gabe!!! Matt is fun, of course. And working hard along with the writers.

[@kendomyers]

Said the tapeworm

[@fensoxx]

Gabe explained black holes to me better than I’ve ever heard it explained. They both shine in their own way. We are damn lucky to have them.

[@neilwilliams929]

I won't say best host ever .......That's a very bold comment "! But matt is very much a great presenter .👍

[@matthewwhite546]

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

[@martiddy]

I'd recommend you to check his other previous videos before watching this one, it will help you to understand some terms and physics processes.

[@PuzzleQodec]

Cute little finger spinors. Sounds good!

[@kareldegreef3945]

well he's full of it => there are no sub atomic particles => that's just a model to understand !!! he's brainwashed as well => there only fields !!! just saying => youre not missing out of much here ;-)

[@closair]

Matthew White so you need Alton Brown’s explaination

[@martiddy]

@@kareldegreef3945 so please tell me how chemistry works then, or how the computer/smartphone that you're using to access to internet works without atoms and electrons.

[@marcusbenjilake]

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

[@Cosmalano]

Bertrand de Born that moment when you don’t like pop science using silly words so therefore all of physics is wrong.

[@Cosmalano]

Bertrand de Born pop science gets people, usually kids, into the subject that become professionals later. And if you seriously think there’s not been any progress in over 70 years in that field you’re either trolling or uneducated. I’m in that field and I assure you there is plenty being done, try reading up on it.

[@Cosmalano]

Bertrand de Born do you know quantum theory or general relativity or are you basing this solely off the claims of others that say they do?

[@Cosmalano]

Bertrand de Born okay so you aren’t a physicist. That’s all I needed to know. Tesla wasn’t a physicist and there is no such person as “Feynstein”. Keep studying.

[@Cosmalano]

Bertrand de Born Einstein has not formal education? That’s patently untrue. Get it? It’s a pun because he worked in a patent office while he was completing his formal education.

[@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.

[@Alpha_beef]

Definitely. Also increasingly highlighting some of the push and pull between math and physics

[@heyMattJay]

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

[@icollectstories5702]

Re-watch the older vids; this one's pretty far down the ol' rabbit hole. This series is trying to guide you step-by-step, so you might have missed one.

[@ChasingTheDelta50]

lol 18 kid who love quantum mechanics: grabs popcorn and is pumped for the new videos on favorite science channel and understands all of it ahhahahaa

[@ugoeze7360]

That’s not brain that’s oozing... 😰

[@mthokozisilanga4497]

MJ Music 🤣🤣🤣

[@chrissonofpear1384]

All about the smallest bits of space being small 'loops' at the Planck scale, where space and time is potentially quantised. And, per some models, spacetime may be itself an emergent phenomena from, say, entanglement itself...

[@xterminal5997]

“bröther, can I has quantum lööps

[@melparadise7378]

🥣

[@TheNamelessOne888]

But X Terminal, you already have quantum loops, too many to caunt.

[@Steevo69]

How about a Moose with a toothbrush?

[@mufaromandaza]

🤣🤣🤣🤣🤣🤣🤣🤣 very funny

[@ujjalshill6442]

But we have quantum loops at home

[@aghosh5447]

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

[@billdooder2558]

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

[@goatmeal5241]

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

[@kendomyers]

Its time we talk...

[@ffggddss]

"If a stranger walks up to you and offers you a loop of quantum gravity candy, ..." Fred

[@naotamf1588]

I just watched the recent Vsauce2 video. From about 8min towards the end Kevin explaines non-transitive loopholes (gamelogic), and that is how It became quite clear to me. Maybe we are in a simulation after all and LQGs are some sort of q-bits in an endless cycle of non-transitive loops batteling out equilibrium?

[@paulmichaelfreedman8334]

say that and their mouths begin to water...Fruit loops is what came to my mind first too...

[@gwddmt1]

*When a quantum Mommy gravity falls in love with a Daddy wave function and they make a special loop connection and...*

[@thepoofster2251]

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!

[@FredDufresne]

Updoot for answer

[@FairyRat]

That's a good bloody question.

[@godm0de]

I lost you at 'if space'

[@SeraphimKnight]

I don't think it works that way. Think of it like zooming an image on a screen; you don't get more pixels on the screen, just the image is stretched across more pixels. At least, that's how I understand this.

[@CharlieLOL]

One dimension we are familiar with. Not necessarily one total. Expansion is a relative term. #oneloopuniverse

[@stephenshortnacy]

"Which is a concept too abstract even for this episode." Hahahaha!

[@believer773]

" I like my gravity loopy, not stringy"

[@photinodecay]

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

[@yawgmoth6568]

No you don't lol.

[@ChadPANDA...]

@don't matter r/woosh

[@kdhavle]

He's Sid, out Fire God!

[@itchykami]

Whoever does your graphics, give them a high-five for me. They are well thought out, and awesome.

[@Tabu11211]

And a second hifive for me. Person needs hifives.

[@LuisFlores-gz9of]

17:22 there you go

[@sakykBzz]

really? i thought they hired a new one for this episode. they were horrible

[@derekokeeffe9919]

another high5 from me

[@thekaboominator1]

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!

[@Eris123451]

"So quickly let's just review all of Quantum Mechanics," best throw away line so far.

[@Ryukachoo]

In today's episode of "holy hell that title's already making my brain hurt" Followed about twenty minutes by "brain hurts a little less but this makes more sense I think?" Followed an hour later by "I still don't get it :("

[@noelegarland]

I've just gotten used to the fact that I'm dumb. I just come here hoping some smart might stick to me if I rub up against it enough.

[@timeisyonger695]

I understand it more then string theory but it is hard (:

[@upgrade1583]

In summary he said.... Life is heaven. Death is hell.

[@Canadian_Ry]

@@noelegarland I'm on that boat. Cheers, my dude.

[@KenMathis1]

I'm here for the journey because I'll never reach the destination.

[@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.

[@bioboy1819]

I would say this is probably one of the best videos, educational monologues, that I have ever had the pleasure of listening to.

[@ZhangRed]

im very thankful for your videos. I have been following since the start of my qft journey. You guys give the big picture of what all this maths is for

[@adammercer9679]

"So just quickly, let's just review all of quantum mechanics." Good one, Matt.

[@velnz5475]

this statement was made at the phanerozoic eon, cenozoic era, quaternary period, holocene epoch, 12019 HE on October 15th; all of quantum mechanics would take longer then the entire phanerozoic eon itself lol. Matt just breezed through in a 17.5 min video...

[@JLocke573]

I think I stroked out after he said "So just quickly let's review all of quantum mechanics"

[@nicolasribeiro7914]

not only you

[@BaronAnon]

So you come home, and there he is, Matt O'Dowd, sitting in your kitchen: "It's time we talked about Loop Quantum Gravity."

[@michaeljubara9397]

Yep, ain’t life wonderful!

[@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.

[@LordMarcus]

I'll never open a can of Spaghetti-Os again without thinking of loop quantum gravity.

[@velnz5475]

wait people eat those? I mean... im surprised its still around

[@aarona493]

I see you've broken down holonomy and spinor bundles into somewhat digestible somewhat normal words, and I optimistically challenge you to do the same for topos theory and quantum logic.

[@Tabu11211]

No idea what that is but I am excited for it.

[@SuviTuuliAllan]

everyone: give us maths spacetime: we don't do that here

[@bobbysanchez6308]

Indeed

[@martiddy]

@@SuviTuuliAllan If you want to know a more mathematical explanation about theoretical physics, then I highly recommend you the channel Sixty Symbols.

[@jovetj]

There are too many types of sleep that we don't know about but experience.

[@thatonevisionary]

One of the most comprehensive videos I’ve seen on this subject yet.

[@Alakazzam09]

I only understand about 20% of the content in these videos but I can't stop watching them.

[@donaldharlan3981]

This is one of the best PBS Space Time episodes I have seen yet. Good shot!

[@kikivoorburg]

Bröther, may I have some *Lööp* gravity?

[@mathematicalninja2756]

Lol

[@olas2012]

You've won the nerd internet today. I applaud you

[@KungKras]

Don't forget to mentally pronounce the "öö" in the Swedish or German way. Otherwise you're missing out.

[@VigiliaMortisYT]

Came here just for this comment xD

[@koenvandamme6901]

*smacks universe* It fits mäny lööps.

[@Ekstrax]

I'm so amazed i understand this, thanks for the awesome explanations every time

[@TenzinLundrup]

Really nice explanation of LQG. Great fun! Thanks to your supporters.

[@WestOfEarth]

I've been watching (and rewatching) Dr Leonard Susskind's lectures on General Relativity. So I think I actually understood most of what you presented here.

[@schizoseahorse]

woo ive been waiting for this episode for so long! as a fan request, could you do one on quantum darwinism or conformal cyclic cosmology (ik the latter you gave a quick reference in a video a bit ago), i feel like especially with the quality of animation you guys have both of those topics would be super lovely to watch a video on

[@7airgear]

If anyone is interested, a really great book on this is "Reality Is Not What It Seems: the journey to quantum gravity" by Carlo Rovelli. He makes the topic super approachable while also going into enough detail that you feel like you actually learned something. I would totally recommend it! (But maybe skip the first couple of chapters because its just kinda superfluous history 😅)

[@ffs55]

Lovely video , THANK YOU. Thank you for not watering this down and great job with reduction.

[@justdave9610]

I'm a simple man. I see a new PBS Space-time video and I press like.

[@HurricaneSA]

Universe: Okay little humans, what is this picture? Humanity: Uhm...it's a ball! Universe: Are you sure? Humanity: Uhm...no, it's a string! Universe: Are you sure? Humanity: I dunno. Oooh, wait, it's a loopy thingy! Universe: Sure about that?...

[@TlalocTemporal]

Cloud? Toroid? Quaternion? Mandelbulb? Little maintenance men with flashlights?

[@berk6240]

kzbin.info/www/bejne/iYmznoWJfdlrbMU interview with Carlo rovelli, one of the founders of loop theory

[@miketate3445]

"So let's just quickly review all of quantum mechanics". Delivered completely straight and dry. I love it.

[@JesseGilbride]

Awesome episode! I'm going to have to watch this a couple more times.

[@federicosello5130]

Awesome, I've been waiting for this!!

[@brandonlewis2599]

How do we think about cosmic inflation and expansion in the context of LQG? Is it new loops being added to the fabric of space? Or just a reconfiguring of the connections between them? Or both? What does a black hole look like in LQG?

[@kindlin]

I really did love this episode, but I want to see a whole nother episode with all of these questions, now, too!

[@jackburton8352]

i am working on theory that i call quantum smearing which comes close to unifying relativity and the quantum world. look out for it early next year looking to publish around March

[@chrissonofpear1384]

Mmm, I would be interested in that, Jack. Also, any thoughts on Doubly Special Relativity? As formulated by Amelino-Camelia and others?

[@jessewintermute8031]

I have absolutely no idea on mostly what you are talking about but I keep coming back because it's interesting and I want to learn

[@benefit14snaake]

Been waiting for this video, thanks.

[@kokomanation]

I think this theory has more potential than string theory because it is much less complicated and it might predict something verifiable

[@vyhozshu]

we should gauge the theories with priority being "that which requires the invention the fewest new invisible dimensions to work" 😁

[@Feroxing12]

dont worry string theorists will add 17 extra dimensions for their formulas to work.

[@harrylerwill8915]

Interesting as always. In a perfect vacuum, modeling the most particle-sparse regions of the universe, is there an expansive effect?

[@PiercingSight]

16:10 - Man! I want to hear more about naked singularities! Looking forward to the episode!

[@Talleyhoooo]

This is actually really intuitive to follow

[@amazingwil]

So your explaining something I have never heard of, this should be interesting.

[@MichaelKilmanAuthor]

You know, I love that this show exists and I have been a patreon supporter for quite a while... but some of these episodes... melt my brain. I am just a poor social scientist! I won't stop watching... but man this channel is intense sometimes.

[@jrersinghaus]

this was such an amazing watch! This actually jogged my mind back to a notion i was contemplating trying to understand gauge theory, for some reason in my head it related to governing of limiting degrees of freedom for subatomic interactions but governance with the shape of extremely small extra dimensional space, when this stuff connects in this conceptual way.... it gives me goose bumps.

[@MonaSchmidtInc]

Very interesting. I wonder why exactly they started with an abstract space of metrics on 3D slices instead of an abstract space of 4D metrics in the first place? I'd love to learn more about this problem of time.

[@ErenJeagerBomb]

Thank you so much for reminding me how little I know, friend. I'm gonna go eat some crayons now.

[@ramonpizarro]

Save me the blue ones, they're my favorite

[@chinkeehaw9527]

A Troll I think you're gonna let someone else do the job considering your name

[@eliomonaco147]

I would like to take a moment to appreciate how unfathomably smart these people are.

[@darioinfini]

I have a theory I want to propose -- most people seem incredibly dumb to me. And then there are people like Matt who are outrageously smart. It seems to me that the same way there is a massive wealth gap with a handful of people owning half the world's wealth, there are a handful of people who are in possession of half the world's intelligence. Call it Intelligence Inequality.

[@brucecampbellschin8632]

If I was as smart as half of these guys I'd be showing off to all the ladies.

[@darioinfini]

@@brucecampbellschin8632 LOL you literally made me laugh. If you were just a little smarter you could have worded that right -- if you were half as smart as these guys... Or maybe you were just proving your point, in which case, on point!

[@brucecampbellschin8632]

@@darioinfini Both I'm at work and it's actually so boring my brain doesn't work properly AND I was falling asleep while watching the video.

[@darioinfini]

@@brucecampbellschin8632 I was awake and I didn't get it either. Was just kidding bro. That guy makes a lot of us feel like we have no clue what's going on. This video I was basically lost from the start. Usually he loses me about 1/2 to 2/3 of the way in.

[@Neura1net]

Great episode as always

[@sankalpachowdhury7378]

I waited for a video on loop quantum gravity... And here it is... ♥️♥️♥️😎 Thank you for making Awsome videos♥️😍

[@Joiner113]

I feel like every time there's some weird shit going on in physics and cosmology, Carlo Rovelli is always involved.

[@LuisAldamiz]

That's a plus, Smolin is also cool.

[@martiddy]

That's when you know you're doing something good as a theoretical physicist.

[@jovetj]

He's got his noose in everything.

[@chrissonofpear1384]

Wait til you hear about Doubly Special Relativity...

[@sebastianbermudez4081]

He's an incredible human being and very charismatic, I really like to hear him speak about physics, reality and life.

[@penisdeletus4601]

Can you make a separate video on the experimental predictions of both string theory and loop quantum gravity ?

[@fgutz1970]

I rarely understand what he's talking about but enjoy hearing him say it.

[@maxrockatansky3896]

Almost like a there was causality universe collided with the singularity and both are intertwined. Definitely awesome channel.

[@tylerislowe]

Since loop quantum gravity defines the smallest possible time as well as the smallest possible measure of area and volume, could it be possible the appearance of wave functions/particles duality arises from the topographical uncertainty of the quantized "space" said particle information has to pass through?

[@keegsmarshall6610]

I certainly wonder about the whole particle/field distinction and whether it needs reexamination.

[@UNLKYHNTR]

Universe *slaps tummy* "It can fit many löps"

[@davidtumm]

Very good explanation. thank you!

[@templarseries]

That's a good explanation, thanks, just what I wanted to know.

[@adolfodef]

09:20 I would have called this theory "Chainmail Spacetime Gravity": CSG [the letters themselves even look like what it is described on each aditional dimension].

[@markyocum8249]

@3:30 "So, just quickly, let's review all of quantum mechanics..." 😂😂😂😂

[@tahah.babikir7698]

you give me the shivers man.

[@Kevin_Street]

Wow... It's going to take a few viewings to understand this, even though you did it an amazingly non-mathematical way. Something tells me this is the most accessible description of Loop Quantum Gravity anywhere.

[@radar9561]

The loops in loop quantum gravity don’t sound that much different from looped strings. I guess the math probably makes it more distinct by not needing multiple dimensions but can you expand on the differences of these fundamental pieces, please?

[@Aleonore22]

Hi Matt! (I'm sure he's going to answer your question)

[@joshuahillerup4290]

They're made of something different

[@loganfisher3138]

One is made of spacetime, one is made of string. That's not a trivial difference.

[@scottmiller4295]

yea or maybe the curled up dimensions or something either way both camps are currently working together to try and bridge the gap where they had been dead set rivals for THE theory rather elitist eh?

[@CasualGraph]

In string theory the loops are particles, in LQG the loops are space, I think.

[@burkhardstackelberg1203]

I remember having commented on LQG in another episode, esp. on its prediction of slowed-down gamma photons - an effect that clearly violates Lorentz invariance. Indeed, LQG, as designed by Lee and Smolin, treats time as an extra variable different from space. I would be really glad to see LQG translated to a manifest Lorentz invariant form...

[@cheker10000]

A deeper video on spin networks would be pretty cool

[@lythd]

This is the first video I've actually had to rewatch. Wow thanks.

[@berk6240]

kzbin.info/www/bejne/iYmznoWJfdlrbMU interview with Carlo rovelli, one of the founders of loop theory

[@TraneFrancks]

Just noticed that you're saying "Ashketar" instead of Ashtekar. Easy to do, I guess. :)

[@anaywalunjkar]

It's an Indian name, hard to pronounce I guess

[@janpeternelj2309]

Wait so Ashtekar is correct? That's the way it was written but he kept saying Ashketar.

[@TraneFrancks]

@@janpeternelj2309 As written is correct.

[@yin-chengkrishuang8405]

8:22 Ashtekar, not Ashketar.

[@marsupius]

Ash guitar

[@jmcsquared18]

13:01 Thank you for mentioning that. That was such an amazing observation. As attractive as loops are to me when compared to strings, they don't seem to agree with the data. As Sagan put it, our preferences don't count.

[@LuisAldamiz]

That's probably only because they haven't hacked time hard enough.

[@kennedystapleton2279]

He did imply that it may have been unmeasurable (to current technology). Stating this, I would love to know if the measurement was made with a significance to confidently count out loop quantum gravity.

[@LuisAldamiz]

@@kennedystapleton2279 - The problem is that there's only been one such measurement, so the confidence is necessarily small. AFAIK the measurement was performed on light traveling from a neutron star collision a very long distance away, collision detected only via gravitational waves. The measurement also suggested that gravity travels a tiny bit faster than light (or that light is delayed a tiny bit more than gravity at such extremely long distances, a more reasonable explanation in principle). More research is needed...

[@JRichardson711]

This makes so much sense on a macro level. GR tells us the background or stage (space) is dynamic, therefor QM must take that into account. Einstein tries this in the 1950’s but it was a mess. In 1965 the Wheeler-DeWitt equation attempts this, but is unsolvable... until you utilize the information in the connections of space. Those ideas and that path seems seem like a very logical way to reconcile GR and QM. This is currently my level of understanding and I get lost in the math beyond that, but it seems like the idea for the structure and form of loops comes from the connections utilized in the math. Going from mathematics and abstract understanding to a solid picture is always the hard part. Moving from analogy towards reality. Love this stuff. Graphics guy or team is amazing. Best in the biz.

[@thePricoolas]

When he said "in spacetime" at 5:51, I gotta say I flinched

[@raulbruh3291]

To those who are interested in loop quantum gravity and perhaps are quite confused about it, I would highly suggest reading the book "Reality Is Not What It Seems" by Carlo Rovelli. It is so beautifully written, and it gives an entirely different perspective on the nature of reality where time does not exist.

[@enterprisesoftwarearchitect]

Raul Lasagna skydivephil’s KZbin channel has a very approachable interview with Ashetekar (spelling?) himself.

[@chrissonofpear1384]

Thanks. Mainly I've been looking at Lee Smolin's books on this sort of thing...

[@fehmeh6292]

"Notre-Dam" *snaps* Too soon. Too soon.

[@adamsmith4559]

IMHO, your best episode ever.

[@binkawy]

Thanks for the video .. very illustrative ..

[@Encephalitisify]

That fractal loop spiral you showed...where can I look at a good 10 minute video of that. That was so awesome. It went 3D.

[@octavianova1300]

One of the biggest things I've always had trouble wrapping my head around about LQG, is why spin is the quantum operator that is used to mathematically represent the fabric of space. In what way does adding quanta of spin - as opposed to any other quantum operator - to the connections used to describe space, make the space of metrics appear just like a space of quantum fields, thus enabling gravity to be quantized, in a way that it could not be with connections built from regular ol' vectors?

[@AliceYobby]

This is a question that can only truly be answered with a PhD

[@Nukestarmaster]

LQG uses spinors for the same reason that String Theory needs 6 (7 for M theory) extra spatial dimensions. That's what makes the math work to produce a model that resembles reality.

[@stevewhitt9109]

The spin in LQG is NOT the same thing in QM

[@Manguadesignz]

Bruddah English pleassssse

[@matthewparker9276]

Something that could be relevant is that point like singularities in GR become loops when they gain angular momentum. If there is a minimum angular momentum (i.e. quantised angular momentum) then any point masses become loops. Idk if that's actually relevant, but it feels like it should be to me, at least on some level.

[@sebbychou]

I love this idea, I hope I'll get to actually understand it...

[@MihaiManuta]

Before: "So... understood mostly nothing of string theory, maybe I'll get this!" After: "F#@k me...!!"

[@jovetj]

This isn't string theory. This is an alternative to string theory.

[@chrissonofpear1384]

There is definitely SOME overlap, but it perceives the link to spacetime a little differently...

[@faaaszoooom6778]

@@jovetj He did not say that they were the same. He said, he did not understand ST, AND he does not understand LQG either.

[@chicxulub2947]

@@jovetj The blasphemy!

[@beenaplumber8379]

I like Matt's presentations. He is easy to understand, though he is delivering some seriously dense content. He doesn't talk like an auctioneer, nor like a teacher talking to a 7 year-old child. That's a terrific balance to strike. I don't claim to fully understand LQG after watching this, but I am quite surprised at how much I learned. I feel I have a basic understanding, enough for an amateur to be getting on with.

[@grandlotus1]

This stuff is so cool. I wish I understood more than just the individual words.

[@kalonji64]

Read all Carlo Rovelli books, even bought his Covariant Loop Quantum Gravity !! Your video is such a good explanation of Ashtekar, Smolin and Rovelli's work... thank you very much for that ! A french fan of the only real quantom gravity theory that could work indeed xDD

[@kalonji64]

And about the time problem in the loop quantum theory, in his books Rovelli well explains that in a when we approach quantum sizes, time seems to be no more needed in the equation so it works even in a 3d space ;) edit : not sure I'm beeing understood, if not, please read Revelli's books xD

[@SuperLoops]

"we live in a seriously Loopy space time" YES THIS 😂😂

[@WackadoodleMalarkey]

Apropo username 😸

[@DarthObscurity]

Could you guys normalize the volume between the intro and Matt's speaking voice? I like to be able to hear him but when the music kicks on it seems way louder then him. Causes some headaches where I live.

[@nicolasblume1046]

Could you do a Video about the big bounce theory and how it works without singularities? I've always wondered why the classic Theorys predict singularities. Couldn't there just be a point where the collapse stops, for example at the Planck length?

[@frantisekstehlik6888]

i'm not saying I understand EVERYTHING, but i'd be lost without the pictures, they really do help

[@TychoBrahe21]

For those interested in gravity, I can whole heartedly recommend a book, Three Roads to Quantum Gravity, excellently written, and somehow makes complex topics understandable without losing (edited from "loosing") the depth of the material.

[@upgrade1583]

gravity is a side effect of mass, how can there be a whole book on it?

[@Joemamahahahaha821]

Upgrade are you kidding?

[@dr.trotter1086]

@@upgrade1583 There is sooooo much we don't know about gravity. Not only is there enough to write a book, there is enough to write entire libraries.

[@scottrokeby4761]

I read that book! Sooo good. For all we know of gravity its still such a mystery.

[@scottrokeby4761]

@@Joemamahahahaha821 I think Upgrade is a troll in training.