The Battle for REALITY: String Theory vs Quantum Field Theory

REFERENCES

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CHAPTERS
0:00 Is String Theory Crazy?
2:19 Why am I in London?
3:28 String Theory and Quantum Field Theory differences
5:16 Why bother with String Theory?
6:52 Why does a graviton need to have no mass and spin 2
7:52 Why no Graviton in Quantum Field Theory?
8:47 String Theory solves quantization of gravity
11:20 Similarity and differences between QFT and String Theory
14:08 Why does String Theory need extra dimensions
15:01 Bottom line on String Theory

SUMMARY:
How is string theory related to quantum field theory? Quantum field theory (QFT) is a mathematical
framework that is close to a theory of everything. It describes nearly all particles and forces in the universe, and is consolidated into an overarching theory - the standard model of particle physics. But it is incomplete because it doesn't explain gravity. Enter string theory, which sounds crazy, mainly because it proposes a universe made of vibrating strings and with at least 10 dimensions! We only know of 4, the three spatial dimensions and time. It claims that at least 6 other dimensions are hidden from us. But it is popular because it has an answer explaining gravity in quantum mechanical terms.

String theory posits that the smallest building blocks of the universe are not point-like particles, but tiny, one-dimensional "strings" that vibrate at various frequencies and in different dimensions. Different combinations of frequency and dimensions describe all the different types of matter, forces and energy in the universe. There are several string theories, all related to a deeper overarching theory called M-theory.

Quantum field theory posits that all particles are excitations in fields that span the entire universe, and that forces are due to the interaction of these particles mediated by other particles called bosons.

Both theories in principle can mathematically describe all particles and forces. But we know quantum field theory works. This is not the case for string theory, but we continue to bother with it is because it can model particle that looks identical to the graviton, the theorized missing boson particle that could quantize gravity.

String theory models a particle with zero mass and spin of 2, which would be a graviton. It needs to have no mass because gravity propagates at the speed of light and has an infinite range. Only a massless boson particle could have such properties. A spin 2 is required to model an exclusively attractive force which is what gravity is.

Quantum Field Theory can also describe gravitons – as excitations in a theoretical graviton field. But the problem with trying to quantize gravity in quantum field theory is renormalization. This is the procedure of making a theory valid to infinitesimally small lengths. When we try to do this, we get infinities in the equations. So quantizing gravity using QFT, doesn’t work.

Unlike QFT, String theory solves the issue of quantizing gravity. But the price we pay is that is that we have to contend with 6 to 7 extra dimensions. This is a problem because these dimensions have never been detected.

Scientists have come up with explanations about where the missing dimensions might be. One is compactification. It's like floss - from far away, it looks like a thin 1D line. But as you look at it more closely, we can see it is 3 dimensional.

Another solution to the missing dimensions is that there could be super dimensional membranes in a 4th dimension isolated from us. We would have to exist outside of our local brane to see these extra dimensions.

If we could detect these extra dimensions, It would be significant evidence indicating that string theory is likely a superior model of the universe, and that QFT is an approximation.

But there are some similarities between QFT and String theory. The amplitude in QFT corresponds to the number of particles, just like the amplitude of the vibrations in string theory also corresponds to the number of particles.
#stringtheory
#quantumfieldtheory
Why does String Theory need all these dimensions? because its mathematics does not work in 4 dimensions. It only works if we allow the strings to vibrate in at least 10 dimensions. Note that extra dimensions could also be theorized in quantum field theories, but we have not needed them to make the theory work. The math works fine as long we ignore gravity.

[beautimous]

I'm absolutely sure we will find the other missing dimensions in the same place my dryer loses my socks.

[harper]

but the idea that a graviton being a force carrier conflicts with the idea that gravity is not a force but a twisting of space-time.

[denissavgir]

I have an idea on how to visualize string theory's extra dimensions. As it's been said that it's impossible for our brains to visualize extra dimensions, this can bypassed by the assertion that the extra dimensions are compactified, so the visualization can remain 3D. Each of the extra compactified dimensions can be visualized by giving an object extra visual properties but keeping their 3D location the same. Imagine a ball. You can visualize it moving through the first 4 dimensions by moving it around and watching it in motion. Then imagine a 5th dimension: moving through a color gradient from blue to red. So now you can move a ball through regular 4D space (its motion being the 4th dimension), and you can move it back and forth through the 5th by changing its color from red to blue or back. You can then add additional visual properties to represent further dimensions. Imagine a conversation between 2 particles: "Hey, I'm here where you told us to meet, at the exact coordinates and at the right time, but I don't see you", "Your x, y, z is correct, and I'm still here. However, you need to come bluer to me. You're too far away off in the red. Come bluer and you'll see me" "Oh ok, I see you now. I must've taken the wrong turn at purple". If you take away an object's innate visual description and give it to the coordinate system, you can represent another dimension by having it represent another dimension's gradient by making it be an arrow that can point in various directions, each direction representing a point on that dimension's gradient. Like an arrow on a speedometer pointing to numbers, it could be pointing at its representive coordinate for that dimension. So if the 6th dimension were represented by a fuel fage, those particles can extend their conversation: "let's go for a stroll. We can keep our x, y, z coordinates, stay in the blue, but we can take a stroll from full to empty and then back. 1 lap". Since motion in the extra dimensions doesn't affect the x, y, z coordinates, this should work, as it remains conistent with the 3D world, borrowing some of its attributes to represent motion in dimensions we can't see, the same way that worldlines on a spacetime diagram borrow the Y dimension to represent time.

[rudiklein]

Exploring theories, even when they eventually don't give us all answers, is never a waste. It enriches our knowledge and often points us in a new direction.

[FabianReschke]

The Nord VPN Placement was hilarious :D

[namonef]

6:51 this is my first time seeing a string theory equation

[kamcashman]

A little late to the party but at 11:14

i like the birth date and date of death for each forefather of mathematics and science being exactly true to fact.

That's why I like arvinash

[hugolouessard]

When talking about quantifying gravity, all we hear about is String theory. I wish there were more videos about loop quantum gravity, it's fascinating

[Paul_Ch]

Ok. This is one of those videos I will need to watch a few more times if there is any hope for me to almost understand. Thanks for the rabbit hole, Arvin.🙂

[rhouser]

Me watching not understanding any of this but really interested

[SANGI]

As doctor who knows absolutely nothing about physics, but loves to learn about it, this video was amazing!!! Keep it up!

[markofdistinction]

I remember taking calculus in college. We were assigned the problem of rotating the y=1/x function around the x-axis to form a cone. Then calculate both the volume and surface area of the cone from x=1 to infinity. The result was a cone with a finite volume, but an infinite surface area. In other words, you could fill it with paint, but couldn't paint the inside.

My point : Just because the math says something .... doesn't mean it reflects reality.

[saftheartist]

How about “Tube Hypothesis”

- tube hypothesis proposes that the fundamental strings in string theory are tubes (possibly two-dimensional) that facilitate vibration, by channeling the flow of spacetime.

[canalpolaris]

In the layered mattresses model, would each field layer actually occupy the same space? It's puzzling to even consider what space is in relation to those many fields. From what I gather the different layers would be thought of most accurately as kind of "fused" in the same space as like different radio stations

[UniverseSpeck]

Great video and breakdown. Quantum Field Theory makes more sense to me. It's how I envision things. I don't like string theory because it describes a string in a singular point of space. I just don't think that's right. That being said, I'm not a physicist or mathematician and I like everyone have a lot of questions. There's no doubt we are missing a lot of the pieces of the puzzle. I think someone will have to come along and really throw a curveball idea to help us make some progress like Einstein did. There's a lot of problems:

1. Dark Energy - Expansion of the Universe caused by who knows what
2. Dark Matter - Massless gravitational phenomena holding galaxies together but we can't figure out what it is. Right, makes sense...
3. Quantum Gravity - How gravity works on the quantum level. My feeling with this is that if we proved that gravitational waves exist, doesn't that inherently prove there is a gravitational field? Sorry I'm a novice
4. Time and Space- I for one really struggle with time and space. What even is time? We describe it as a dimension, but to me it's less a dimension and more a law of change/entropy. The more space things occupy or warp, the slower time/entropy occurs. Weird dude.
5. A million other things we don't know....

Anyway, I have to get back to my life, its a funny world. Someone smarter than me will figure it out.

[aminetajjiou]

At 11:15 the dates of birth of Newton and Einstein are switched

[MessedUpSystem]

Actually, String Theory is a type of Quantum Field Theory, it is a QFT of D scalar fields living on the 2D world-sheet of the string

[effectingcause]

Uniting quantum mechanics and relativity will only lead to more questions, it won't be the theory of everything we hoped for. A true theory of everything must be able to account for all of the fundamental constants of nature. If a theory can be used to derive the values of all fundamental constants of nature, then we will finally have the Theory of Everything.

[gregcampwriter]

The thing I always wonder is what gets the mattress vibrating in the first place?

In my case, it takes an alarm clock that can't be ignored.

[hardikparekh]

Like always, brief, concise and to the point description of comparison between QFT and ST.. Request you to make similar video describing the comparison between QFT and LQG (Loop Quantum Gravity).