QFT/GR whats the problem? I can't see one

  • Thread starter taylrl3
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In summary, Quantum Field Theory is incompatible with General Relativity because general relativity is non-renormalizable.
  • #1
taylrl3
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Hi,

Im just wondering why Quantum Field Theory is incompatible with General Relativity. From my current understanding they seem to be compatible. I must be missing a crucial piece of information. Please help :-)

Talyl
 
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  • #2
Ok, we have potentials and particles. Why can't you have a discreet amount of a field?
 
  • #3
One of the most commonly quoted reasons is that general relativity is non-renormalizable. In other words, the procedures used to prevent certain calculations from giving infinite results don't work for GR. I'm not (yet) familiar enough with the topic to explain that offhand, but maybe someone else can fill in the details.
 
  • #4
Yea I have heard about this renormalisation problem too. Ill go and see if I can read up on it and come back with a post.
 
  • #5
Hi,

So the problem with general relativity is that its perturbativly non-renormalisable. You can see this just from power counting arguments since Newtons constant is dimensionful. This means that when you add counter terms to the action, to cancel the divergences from loop diagrams, these will general not have the same form as the original action. This doesn't stop one treating gravity as an effective field theory though; as long as you only consider process with typical energy E<<M_pl where M_pl is the Planck mass QFT/GR are perfectly compatible.


http://en.wikipedia.org/wiki/Effective_field_theory

One should also note that the breakdown of perturbative QFT at the Planck scale does not necessarily imply that a non-perturbative formulation of gravity as a QFT is impossible.

http://arxiv.org/abs/0709.3851
 
  • #6
taylrl3 said:
Hi,

Im just wondering why Quantum Field Theory is incompatible with General Relativity. From my current understanding they seem to be compatible. I must be missing a crucial piece of information. Please help :-)

Talyl

Besides the one mentioned , non-renormalisability of Gen Rel., there appears to be some other difficulties.

One is that in QFT the time component has, at least in part, an absolute (Newtonian) character as opposed to the full dynamic (space)time of Gen Relativity.
See here for example: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TVN-4S6G8XP-2&_user=10&_coverDate=05%2F15%2F2008&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1430883942&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=ea2de960d543c63799c7fbefc113ff0a
I'm not so sure this problem has been successfully circumvented , even in Quantum Gravity.
However, that is not exactly my area of expertise.
...
 
Last edited:

1. What is the problem with combining Quantum Field Theory and General Relativity?

The problem with combining Quantum Field Theory (QFT) and General Relativity (GR) is that they are two fundamentally different theories that do not easily fit together. QFT describes the behavior of subatomic particles and their interactions, while GR describes the behavior of gravity on a large scale. These theories use different mathematical frameworks and have different conceptual foundations, making it difficult to reconcile them into a single unified theory.

2. Can QFT and GR be combined into a single theory?

Many physicists believe that QFT and GR can be combined into a single unified theory, often referred to as a "theory of everything." However, there is currently no consensus on how to achieve this, and it remains a major challenge in theoretical physics.

3. What are some proposed solutions to the problem of combining QFT and GR?

Some proposed solutions include string theory, loop quantum gravity, and the holographic principle. These theories attempt to reconcile the differences between QFT and GR by introducing new concepts and mathematical frameworks.

4. How does the problem of combining QFT and GR affect our understanding of the universe?

The inability to reconcile QFT and GR into a single theory limits our understanding of the fundamental laws that govern the universe. It also hinders our ability to make accurate predictions about the behavior of matter and energy on both a microscopic and macroscopic scale.

5. Are there any experimental evidence for the incompatibility of QFT and GR?

So far, there is no direct experimental evidence that proves the incompatibility of QFT and GR. However, there are areas where the two theories make contradictory predictions, such as the behavior of matter at the center of a black hole. This suggests that our current understanding of these theories is incomplete and further research is needed to reconcile them.

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