Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: gravity and quantum mechanics

Learn more physics!

Most recent answer: 05/25/2018
Q:
We assume gravity to be curvature of space-time caused by mass, rather than being a force. Then how is it possible to unify gravity with other forces of nature? And isin't is futile to search for graviton particle?
- Amandeep Kumar (age 28)
Bangalore,Karnataka,India
A:

Nobody knows yet how that unification might work. It's too early to give up on string theory and other ideas in which large-scale spacetime emerges from some more general quantum theory. The version of quantum mechanics that is taught in introductory courses, in which everything occurs on a spacetime background, would just be a limiting form.

it is usually said that gravitons must exist because any non-quantized field would allow violations of the uncertainty relation and unravel the whole quantum framework. If I undersand correctly, my colleague Gordon Baym has argued that the small-scale fuzz in the spacetime fabric due to its coupling to other quantum fields would suffice to avoid such problems. (https://pdfs.semanticscholar.org/b381/bf74399d419f69b30d1e5fddc72774168159.pdf
https://pdfs.semanticscholar.org/b381/bf74399d419f69b30d1e5fddc72774168159.pdf)

Still, it's quite possible that ordinary gravity waves on a flat spacetime background are quantized just like everything else, so that that gravitons would exist. If so, they may lead to detectable effects from primordial quantized gravity waves in an inflationary big bang. At one point, it was thought that these had been observed, but that turned out to be mistaken. Still, there's hope that some might be found in more sensitive observations.

Mike W. 


(published on 05/25/2018)

Follow-up on this answer.