Is Quantum Field Theory Still Relevant in Modern Physics?

[Sussan]

What ever happened with QFT? Heard so much about it years ago now only once in a while will a past Nobel laureate state it is real. I know string is the thing now. Any thoughts?
Sussan

 

[strangerep]

What ever happened with QFT? Heard so much about it years ago now only once in a while will a past Nobel laureate state it is real.

"Real"? Huh?? QFT is a framework, in which the Standard Model of Elementary Particles is formulated. The correspondence between quantities predicted by this model and actual experimental results are among the best (most accurate) in all of physics.

I know string is the thing now.

Actually, for purposes of physics, it's becoming more and more of a sad joke.

 

[stevendaryl]

What ever happened with QFT? Heard so much about it years ago now only once in a while will a past Nobel laureate state it is real. I know string is the thing now. Any thoughts?
Sussan

QFT is still the theory used to describe every force except gravity: QED is a QFT for electrodynamics, QCD is a QFT for quark interactions, and the Weinberg-Salaam model is a QFT for the weak interactions. String theory is a special kind of QFT.

QFT is just quantum mechanics applied to the situation with an indefinite number of particles, where particles can be created or destroyed in interactions.

 

[Avodyne]

QFT is alive and well as the most precise and accurate mathematical description of physical phenomena that we have. But because of problems with incorporating gravity (it can be done but requires a QFT with an infinite number of parameters), many believe some further structure (such as string theory) is needed.

 

[bhobba]

Actually, for purposes of physics, it's becoming more and more of a sad joke.

Sigh.

Too true.

To the OP, interestingly a connection between the two has been found that may yet prove of value:
http://en.wikipedia.org/wiki/AdS/CFT_correspondence

Thanks
Bill

 

[Avodyne]

Actually, for purposes of physics, it's becoming more and more of a sad joke.

That's a completely ridiculous and absurd statement. String theory is by far the most promising approach to a quantum theory of gravity. In fact, it provides a perfectly fine theory of quantum gravity (with a particular set of other particles) in 10 spacetime dimensions. Now, as it happens, we see 4 spacetime dimensions, not 10, and that set of particles is not the set that we see. But no other approach to quantum gravity has come anywhere close to achieving this level of success.

Furthermore, it is understood how to get from 10 to 4 dimensions, and how to get different sets of particles. The problem is that you can get many (possibly an infinite number) of different sets of particles in different numbers of dimensions, and there does not seem to be any principle that would select just one of these (let alone select the Standard Model as that one). So what we see may just be an accident, just like the orbits of the planets in our solar system are accidents (contrary to what Kepler wanted, that the orbital radii were fundamental numbers related to the platonic solids). Physicists who want to discard string theory because it seems to be telling us that particle types, masses, and couplings are like the orbits of the planets (just accidental numbers in our neighborhood) may find themselves sharing a room with Kepler in the halls of history.

 

[bhobba]

and there does not seem to be any principle that would select just one of these (let alone select the Standard Model as that one).

Has it been shown yet to contain the standard model?

That's the issue I have with it. It holds great promise, but until the above is done I remain skeptical.

That's not to say I side with those that say its not a physical theory and just math - I find that proposition absurd because of its basis in quantizing strings, but its promise still seems a long way from being fulfilled.

Thanks
Bill

 

[Sussan]

That's a completely ridiculous and absurd statement. String theory is by far the most promising approach to a quantum theory of gravity. In fact, it provides a perfectly fine theory of quantum gravity (with a particular set of other particles) in 10 spacetime dimensions. Now, as it happens, we see 4 spacetime dimensions, not 10, and that set of particles is not the set that we see. But no other approach to quantum gravity has come anywhere close to achieving this level of success.

Furthermore, it is understood how to get from 10 to 4 dimensions, and how to get different sets of particles. The problem is that you can get many (possibly an infinite number) of different sets of particles in different numbers of dimensions, and there does not seem to be any principle that would select just one of these (let alone select the Standard Model as that one). So what we see may just be an accident, just like the orbits of the planets in our solar system are accidents (contrary to what Kepler wanted, that the orbital radii were fundamental numbers related to the platonic solids). Physicists who want to discard string theory because it seems to be telling us that particle types, masses, and couplings are like the orbits of the planets (just accidental numbers in our neighborhood) may find themselves sharing a room with Kepler in the halls of history.

Why such hostility between string theorist and OFT supporters? kinda shocked by the anger when I just asked a as it now appears a not so simple question.
Sussan

 

[Sussan]

"Real"? Huh?? QFT is a framework, in which the Standard Model of Elementary Particles is formulated. The correspondence between quantities predicted by this model and actual experimental results are among the best (most accurate) in all of physics.

Actually, for purposes of physics, it's becoming more and more of a sad joke.

Thanks for the reply. I was asking because I just watched a video from YouTube about a book "Fields of color" from a Dr. Rodney Brooks about QFT and he implies that QTF is kinda a "lost" idea. He made me wonder so just asking.
Sussan

 

[stevendaryl]

Why such hostility between string theorist and OFT supporters? kinda shocked by the anger when I just asked a as it now appears a not so simple question.
Sussan

As I said, string theory is a type of quantum field theory.

The hostility I think is just a reaction to the initial promise of string theory. When string theory really started getting some steam, it promised to be the long-awaited theory of everything, uniting quantum physics and gravity. But then it turned out to be much harder than anyone thought to extract testable predictions from string theory, and so many people soured on it, and started calling it "not even wrong".

So the hostility is between those who still believe in the initial promise of string theory, and those who have decided it's a lot of hype with nothing real to show for all the work put into it.

 

[Vanadium 50]

You seem to think it's either QFT or Strings. This is wrong. The idea behind strings is that the Standard Model (of which QFT is a part) would be embedded inside a correct string theory, if we knew what that was.

 

[atyy]

Why such hostility between string theorist and OFT supporters? kinda shocked by the anger when I just asked a as it now appears a not so simple question.
Sussan

There is no hostility from string theory towards QFT. The standard model of particle physics is formulated in the language of QFT. The standard model has been standard for many years, having passed all experimental tests to date. When you hear of the Higgs mechanism or supersymmetry, those again are formulated in the language of QFT. Even quantum gravity at the low energies of our everyday world is described in the language of QFT. In other words, no one expects the language of QFT to fail except perhaps in the domain of quantum gravitational effects at very high energies.

What language is needed to describe quantum gravity at high energies is still unknown. String theory is certainly the leading candidate for a theory of quantum gravity at high energies. Even if it turns out to be experimentally false, it will hopefully help us learn the right language for quantum gravity. Remarkably, the language of QFT is thought to describe a sector of string theory, but holographically. Thus usually, a 4 dimensional spacetime is described by a 4 dimensional QFT. In string theory, a 4 dimensional spacetime is thought to be describable by a 3 dimensional QFT.

 

[Sussan]

There is no hostility from string theory towards QFT. The standard model of particle physics is formulated in the language of QFT. The standard model has been standard for many years, having passed all experimental tests to date. When you hear of the Higgs mechanism or supersymmetry, those again are formulated in the language of QFT. Even quantum gravity at the low energies of our everyday world is described in the language of QFT. In other words, no one expects the language of QFT to fail except perhaps in the domain of quantum gravitational effects at very high energies.

What language is needed to describe quantum gravity at high energies is still unknown. String theory is certainly the leading candidate for a theory of quantum gravity at high energies. Even if it turns out to be experimentally false, it will hopefully help us learn the right language for quantum gravity. Remarkably, the language of QFT is thought to describe a sector of string theory, but holographically. Thus usually, a 4 dimensional spacetime is described by a 4 dimensional QFT. In string theory, a 4 dimensional spacetime is thought to be describable by a 3 dimensional QFT.

Hi and thanks,

Makes a whole lot of sense. For a while there thought a "war' was about to break out (ha ha).
Sussan

 

[ZapperZ]

This is a very odd thread and a puzzling discussion. You might as well question what happened to Quantum Mechanics!

Please note that the physics that we use to describe the properties of the material you are using in your electronics often uses QFT! So you'll understand why many of us find your question to be unusually strange.

Zz.

 

[Sussan]

This is a very odd thread and a puzzling discussion. You might as well question what happened to Quantum Mechanics!

Please note that the physics that we use to describe the properties of the material you are using in your electronics often uses QFT! So you'll understand why many of us find your question to be unusually strange.

Zz.

Hi Zz,

I totally understand your concerns. Yes it is a “stupid” question for someone in the “field” and at times I have been called stupid, however as referring to this question I am more dumb than stupid. I did attend O.S.U. 1 year in honors level physics, however life had other plans thus married had children you know the movie. My IQ is around 135 (not the brightest bulb in this room for sure) did so-so in Calculus 1,2,3 (B average), so that being stated “should” be able to grasp the Higg’s concept if I just work at it with more diligence than most… which in turn led me here. After learning Hawkins was betting against the Higg’s Boson being found sparked my curiosity thus my layman (laywoman) journey as it were. Well I watched many YouTube videos about the Higgs and most stated analogies that to my mind does seem “stupid” snow, molasses, people in a room (please). I did come across Leonard Susskind’s (Demystifying The Higg’s Boson) an easy as pie to understand the “reasoning” for the understanding, however Susskind would make up names and events that threw my mind into confusion (not a hard thing to accomplish) so joined the forum to ask questions. The Higg’s field is that which actually “gives” in a sense matter weight not the boson which I kind of felt was the case. That led to Fields and that to QFT so watched several videos on QFT and though was ALL mathematical which was pretty easy to understand (means I actually could follow it to a degree) could feel that struggle between String Theorist and QFT Theorist were not commenting on both just their fields. Susskind String man would not say a word about QFT in his lectures and Michio Kaku another String man would not say anything of substance about QFT then I came across a video for QFT “Fields of Color” by Dr. Rodney A. Brooks that was “suppose” to give me a layman’s feel for QFT well in the video he talks about QFT as if it were a “lost” area of physics and went on to state Feynman was a particle man ONLY and did not believe in fields at all so here I am please help me understand.
Thanks Zz

 

[ZapperZ]

Hi Zz,

I totally understand your concerns. Yes it is a “stupid” question for someone in the “field” and at times I have been called stupid, however as referring to this question I am more dumb than stupid. I did attend O.S.U. 1 year in honors level physics, however life had other plans thus married had children you know the movie. My IQ is around 135 (not the brightest bulb in this room for sure) did so-so in Calculus 1,2,3 (B average), so that being stated “should” be able to grasp the Higg’s concept if I just work at it with more diligence than most… which in turn led me here. After learning Hawkins was betting against the Higg’s Boson being found sparked my curiosity thus my layman (laywoman) journey as it were. Well I watched many YouTube videos about the Higgs and most stated analogies that to my mind does seem “stupid” snow, molasses, people in a room (please). I did come across Leonard Susskind’s (Demystifying The Higg’s Boson) an easy as pie to understand the “reasoning” for the understanding, however Susskind would make up names and events that threw my mind into confusion (not a hard thing to accomplish) so joined the forum to ask questions. The Higg’s field is that which actually “gives” in a sense matter weight not the boson which I kind of felt was the case. That led to Fields and that to QFT so watched several videos on QFT and though was ALL mathematical which was pretty easy to understand (means I actually could follow it to a degree) could feel that struggle between String Theorist and QFT Theorist were not commenting on both just their fields. Susskind String man would not say a word about QFT in his lectures and Michio Kaku another String man would not say anything of substance about QFT then I came across a video for QFT “Fields of Color” by Dr. Rodney A. Brooks that was “suppose” to give me a layman’s feel for QFT well in the video he talks about QFT as if it were a “lost” area of physics and went on to state Feynman was a particle man ONLY and did not believe in fields at all so here I am please help me understand.
Thanks Zz

Say what?!

Zz.

 

[WannabeNewton]

I was asking because I just watched a video from YouTube about a book "Fields of color" from a Dr. Rodney Brooks about QFT and he implies that QTF is kinda a "lost" idea.

Well gee I hope not otherwise I'm really wasting my time learning it. I can't even get a refund on my textbooks at this point.

 

[Sussan]

Say what?!

Zz.

Zz!

Really? After all that typing that is what I get? That being stated the Despicable Me minion quote was rather cute, so you do get "partial" credit of that one.
Sussan

 

[Sussan]

Say what?!

Zz.

Well Zz the Despicable Me Quote from the Minion was really cute! So you do get partial credit!
Sussan

 

[mitchell porter]

I think we're all somewhat perplexed by the claim that quantum field theory is a neglected theoretical framework, given that it is the bread and butter of high energy physics. There are two things that Brooks might be referring to.

First, in science popularization, you hear much more about quantum mechanics than you do about quantum field theory. But quantum field theory is just quantum mechanics applied to fields.

Second, a lot of QFT can be described in terms of particles. Perhaps you could say that Feynman invented much of the particle formalism of QFT, whereas Schwinger developed the field formalism, and Brooks is trying to evangelize Schwinger's perspective.

But the practical experience of most people who learn QFT is a hybrid of the two. They will start with field equations, interpreted quantum mechanically, but then quickly pass to the particle formalism. It's only for more advanced topics that the full field-theoretic picture becomes indispensable.

 

[Sussan]

Quantum Field Theroy?

I think we're all somewhat perplexed by the claim that quantum field theory is a neglected theoretical framework, given that it is the bread and butter of high energy physics. There are two things that Brooks might be referring to.

First, in science popularization, you hear much more about quantum mechanics than you do about quantum field theory. But quantum field theory is just quantum mechanics applied to fields.

Second, a lot of QFT can be described in terms of particles. Perhaps you could say that Feynman invented much of the particle formalism of QFT, whereas Schwinger developed the field formalism, and Brooks is trying to evangelize Schwinger's perspective.

But the practical experience of most people who learn QFT is a hybrid of the two. They will start with field equations, interpreted quantum mechanically, but then quickly pass to the particle formalism. It's only for more advanced topics that the full field-theoretic picture becomes indispensable.

Thanks a bunch! Very well put and makes total sense. Now I understand so those that chose QFT solely are in a few words MUCH DEEPER in the area than QM people which use it more as a tool than a "field". Is this right?
Sussan

 

[wotanub]

He meant "field" in the sense of "something that has a value at each point in space-time" rather than as in "a field of study".

Take a look at this picture for a succinct explanation:

QFT is a class of theories, and string theory is one of them. Other examples of QFTs include QED, and QCD.

Some classical field theories (classical meaning that they are not quantized) are general relativity and classical electrodynamics.

 

[ZapperZ]

I think we're all somewhat perplexed by the claim that quantum field theory is a neglected theoretical framework, given that it is the bread and butter of high energy physics.

I will add that it is bread and butter for many areas of physics, especially condensed matter physics. I will also emphasize that a large majority of "tests" of QFT come out of condensed matter physics, which is able to make complex systems that can make clear, unambiguous demonstration of the various aspects of QFT.

Zz.

 

[Hornbein]

Thanks for the reply. I was asking because I just watched a video from YouTube about a book "Fields of color" from a Dr. Rodney Brooks about QFT and he implies that QTF is kinda a "lost" idea. He made me wonder so just asking.
Sussan

I've read Brooks' intro. He was inspired by a three-year (!) series of lectures by Julian Schwinger which Brooks attended. He is saying that Julian had a better conceptual framework than did his buddy Richard Feynman, but Feynman's more accessible view has become dominant. Julian emphasized fields, Feynman leaned toward particles.

As far as I can tell without reading his book, Brooks is emphasizing that particles are localized excitations of a field. I think he is correct in that popular expositions of physics do not emphasize this as they should. Instead "wave-particle duality" and so forth are discussed. Brooks identifies this field-centric view with QFT, which is a bit weird. The particle-centric view is also QFT. But he knows what he's talking about.

 

[RogerWest]

In a recent letter that Rodney Brooks published in Washington Post, titled "Physics That Makes Sense," he says: https://www.washingtonpost.com/opin...c19f06-2ccd-11e6-b9d5-3c3063f8332c_story.html

 

[DarMM]

As others have said, Quantum Field Theory is the foundation of both modern particle physics and condensed matter physics, which is roughly (it's probably the biggest area in physics) the study of how the properties of substances and how those properties arise from atoms and molecules). So it's the bedrock of a large area of modern physics.

String Theory is a framework mainly aimed at describing the world at a lower level/higher energies than quantum field theory. So far there is no experimental evidence that it is correct.

If you're looking into physics, even at a "lay" level, I'd read make QFT the higher priority.

 

[bhobba]

In a recent letter that Rodney Brooks published in Washington Post, titled "Physics That Makes Sense," he says: https://www.washingtonpost.com/opin...c19f06-2ccd-11e6-b9d5-3c3063f8332c_story.html

For those starting out in QM Rodney Brooks Fields Of Color is a good place to begin:
http://www.quantum-field-theory.net/

Looking at QM objects as a field really does solve many beginner questions.

Thanks
Bill

 

[stevendaryl]

In a recent letter that Rodney Brooks published in Washington Post, titled "Physics That Makes Sense," he says: https://www.washingtonpost.com/opin...c19f06-2ccd-11e6-b9d5-3c3063f8332c_story.html

Hmm. It seems strange to say that Feynman didn't accept quantum field theory.

 

[Ilja]

That's a completely ridiculous and absurd statement. String theory is by far the most promising approach to a quantum theory of gravity. In fact, it provides a perfectly fine theory of quantum gravity (with a particular set of other particles) in 10 spacetime dimensions. Now, as it happens, we see 4 spacetime dimensions, not 10, and that set of particles is not the set that we see. But no other approach to quantum gravity has come anywhere close to achieving this level of success.

Wrong. What I have read about strings as a quantum theory of gravity, it is only a hope, based on some of the infinities not being present, that all the others may go away somehow too. Something reached for the numbers 1,2,3 when it would be necessary for all n. And, moreover, only for unbroken supersymmetry, which has nothing to do with the observed universe.

And the competition in this domain is simply ignored. We know how to quantize condensed matter theories, which defines a straightforward way to quantize gravity, namely an ether theory of gravity where gravity is described by condensed matter equations in a Newtonian background. Such a theory exists, and is published, but ether is anathema and therefore ignored. Non-renormalizability of gravity is also unproblematic in this approach, given that a continuous ether theory is, from the start, only a large distance limit, thus, only an effective field theory.

With incorporating the SM and explaining most of its properties the ether is also much better than strings. http://arxiv.org/abs/0908.0591 published in Foundations of Physics, vol. 39, nr. 1, p. 73 (2009) and ignored after this because it is an ether theory, predicts all three generations of fermions together with the SM gauge group.

I'm not allowed to present and discuss this theory here, again, because it is evil ether theory, anathema, but I think I'm at least allowed to answer claims that such a theory does not exist. For discussing it, we would have to find other places, I can propose http://ilja-schmelzer.de/forum/