Can Quantum Field Theory Be Applied to Gravity as It Was to Electromagnetism?

[tenzin]

[SOLVED] Quantum theory of gravity

Does anyone know if the same field theory approach that was applied to the electromagnetic force (resulting in QED) has been attempted with gravity. This would entail ignoring GR and trying to develop a quantum field theory of gravity from scratch. Any insights?

 

[lethe]

Originally posted by tenzin
Does anyone know if the same field theory approach that was applied to the electromagnetic force (resulting in QED) has been attempted with gravity. This would entail ignoring GR and trying to develop a quantum field theory of gravity from scratch. Any insights?

yes, this was tried. the theory is nonrenormalizable.

 

[tenzin]

Further info

Could you mention any further reading on this.

 

[lethe]

Originally posted by tenzin
Could you mention any further reading on this.

are you looking for something to read for laymen, or something for physicists?

what exactly is your level of education? it helps to know this before making a recommendation.

 

[tenzin]

Originally posted by lethe
are you looking for something to read for laymen, or something for physicists?

what exactly is your level of education? it helps to know this before making a recommendation.

Level is not an issue.

 

[lethe]

Originally posted by tenzin
Level is not an issue.

well, then i recommend stephen weinbergs textbook on quantum field theory.

 

[tenzin]

Which one, there are 3 volumes.

 

[lethe]

Originally posted by tenzin
Which one, there are 3 volumes.

well, i am at my parents for winter break, so i can t look at my copy right now, but if i recall, i m pretty sure this is in volume one. in the chapter on renormalization.

you can actually sum up the reason for the nonrenormalizability of gravity very simply: it all stems from the fact that the gravitational coupling constant is dimensionful. but to see what this has to renormalization, you have to learn renormalization first.

 

[tenzin]

I understand renomalization. From the point of view of QED. It is a series with infinite terms, each representing the probability of a partile interaction, which does not converge. Therefore, the idea of renomalization does away with the infinities.

 

[lethe]

Originally posted by tenzin
I understand renomalization. From the point of view of QED. It is a series with infinite terms, each representing the probability of a partile interaction, which does not converge. Therefore, the idea of renomalization does away with the infinities.

well, good for you.

 

[tenzin]

The question is do you know or are you just using big words.

 

[lethe]

Originally posted by tenzin
The question is do you know or are you just using big words.

really? i didn t know that was the question.

i thought the question was this:

Originally posted by tenzin
Does anyone know if the same field theory approach that was applied to the electromagnetic force (resulting in QED) has been attempted with gravity. This would entail ignoring GR and trying to develop a quantum field theory of gravity from scratch. Any insights?

but if you want to ask the question about what i know, or whether i only like to use big words, instead of something about physics, here is the answer:

mind your own fvcking business, and don t worry about what i know or don t know.

 

[tenzin]

I understand renormalization and have demonstrated that. You on the other hand have talked about it but have not demonstrated that you are doinging anything more than plagiarizing a book that you probably don't understand to begin with. If you are going to talk the talk, walk the walk.

 

[lethe]

Originally posted by tenzin
I understand renormalization and have demonstrated that. You on the other hand have talked about it but have not demonstrated that you are doinging anything more than plagiarizing a book that you probably don't understand to begin with. If you are going to talk the talk, walk the walk.

here you go again, assuming that you know what i understand and what i don t understand.

i ll tell you what: shut the fvck up about me, don t say anything else about what you think i know or understand, and i will leave this thread, and neither talk the talk nor walk the walk. i can leave the talking and walking to you, our new resident expert.

 

[tenzin]

Originally posted by lethe
here you go again, assuming that you know what i understand and what i don t understand.

i ll tell you what: shut the fvck up about me, don t say anything else about what you think i know or understand, and i will leave this thread, and neither talk the talk nor walk the walk. i can leave the talking and walking to you, our new resident expert.

I have good evidence to assume that you don't know. You talked about something and then why called on it you can't produce evidence that you understood what you were talking about. This is called a poser.

All you have to do to prove me wrong is show that you know what you are talking about instead of copying out of a book.

 

[lethe]

Originally posted by tenzin
I have good evidence to assume that you don't know. You talked about something and then why called on it you can't produce evidence that you understood what you were talking about. This is called a poser.

you never asked me to produce evidence that i understand renormalization. you asked me for a reference for further reading. which i provided.

i certainly could explain renormalization, but i see no reason to prove myself to you.

i don t believe i said anything that showed that i don t understand what i am talking about, but if that is your opinion, you are certainly entitled to it.

if you think my understanding is imperfect, or my explanation less than lucid, you could simply ask for opinions of other posters, or ask me for further explanation. instead you chose to attack me personally, claiming that i plagiarize, or that i don t understand physics.

and to that kind of attack i can only respond with: fvck yourself.

All you have to do to prove me wrong is show that you know what you are talking about instead of copying out of a book.

like i said, i don t need to prove you wrong.

 

[tenzin]

See I told you don't know it. Why would you give yourself so much stress when all you had to do was admit you don't know it. The only explanation for your behavior is that you are hiding something.

BTW, I can go on all day.

 

[lethe]

Originally posted by tenzin
See I told you don't know it. Why would you give yourself so much stress when all you had to do was admit you don't know it. The only explanation for your behavior is that you are hiding something.

let me tell you something, you know renormalization about as much as my cat. you are an ignorant crackpot, and your attitude here ensures that you will remain that way.

BTW, I can go on all day.

who the fvck cares how long you can go?

 

[tenzin]

Originally posted by lethe
let me tell you something, you know renormalization about as much as my cat. you are an ignorant crackpot, and your attitude here ensures that you will remain that way.

Prove it.

 

[lethe]

Originally posted by tenzin
Prove it.

you have done it for me.

 

[alexsok]

That was a fluent transfer from a nonbelligerent conversation to imprecations, maledictions and what not! :)

 

[tenzin]

Originally posted by alexsok
That was a fluent transfer from a nonbelligerent conversation to imprecations, maledictions and what not! :)

Once again big words that can be expressed in everyday language. Not surprised.

 

[alexsok]

Originally posted by tenzin
Once again big words that can be expressed in everyday language. Not surprised.

So far you have not proven anything around here, but instead got yourself involved in futile arguments, which quite frankly, lead nowhere!

You would be better off checking out that last paper published today (i think), it might be of some interest to you:

http://arxiv.org/physics/0401005

 

[marcus]

mentioning further (online) reading

tenzin said:

Quantum theory of gravity
Does anyone know if the same field theory approach that was applied to the electromagnetic force (resulting in QED) has been attempted with gravity. This would entail ignoring GR and trying to develop a quantum field theory of gravity from scratch. Any insights?
------------------------------

lethe said:


yes, this was tried. the theory is nonrenormalizable.

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tenzin continued:

Could you mention any further reading on this.

---------------------------------------

tenzin's initial question was historical in nature
"does anyone know if a QED-style QFT has been tried with gravity?"

the history of attempts to quantize gravity goes back before 1960 and it is kind of interesting to see what people have tried. Appendix B of Rovelli's textbook "Quantum Gravity" is all about
the history
and a draft of it is online at Rovelli's homepage

http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html

It is well worth the 10 minutes or so it takes to download and
convert the PDF file
-------------------

something like the idea tenzin suggests was tried at least as early as 1952
(see Rovelli page 292) and sometimes called the "flat space quantization"

as tenzin indicates it involves throwing out the basic GR idea of a dynamic changeable geometry and working with a fixed (in this case flat) background space.

after all, QED and other quantum field theories are built on a fixed background geometry, chosen at the outset, which makes them incompatible with General Relativity at a fundamental level. GR is background-independent.

tenzin, I would say that your question points up something very fundamental about approaches to quantum gravity---for 50 years or so there has been this split: some approaches are background-independent (like GR itself and like Loop Gravity) and some are not (like string/brane approaches, and that earlier QFT 1952 approach)

----------------

In 1971, 't Hooft and Veltman start studying the renormalizability of GR and "almost as a warm-up exercise" (Rovelli page 295) they tackle Yang-Mills first---and this wins them the Nobel prize.

But by 1973 they have found evidence that gravity is not renormalizable----that is in this "flat space" or so-called "covariant", fixed-background field theoretical approach.

Calling this approach "covariant" is customary and I believe goes back to the fact that the usual flat space is Minkowski space, the space of special relativity---covariant here refers to the symmetries of special relativity.

------------
By 1975, Rovelli says, it is generally accepted that the flat space approach is not renormalizable. After that the history of quantum gravity divides into two streams

keeping GR and its basic ideas of background-independence and (smooth) invariance intact leads to several background-independent approaches such as Loop

trying to save the "flat space" approach of field theory and high-energy-physics, by replacing GR with something else (that reproduces GR at low energy limit) leads to Stringy theories.

Rovelli tracks the history of these two lines of research up to near the present.

A good description of the "Divide" is on page 302. It has quotes from representative people----a field theorist/particle theorist on one hand, a relativist (GR specialist) on the other. (Note that when Rovelli says "relativity" he means General R, not Special R.

-----------
amazing how true that old proverb is about
those who don't pay attention to history
being doomed to repeat it

the 70 year history of quantum gravity is fascinating, I find,
and I kind of wish more people would look at Rovelli's
condensed outline of it. Pages 287-303.