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Q & A: gravity and quantum mechanics

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Most recent answer: 07/31/2013
Q:
If the big problem between quantum physics and relativity is how the theories treat how mass changes space/time, why can't quantum physics theories just assume that small masses have such a negligible effect on everything as to be effectively nonexistent? I'm sure that their is a reason, but I would like to know why. Thanks guys!
- Gerrit Bruhaug (age 18)
Billings, Mt, USA
A:

The problem isn't so easy to get rid of. If I understand correctly, if you start with some small gravitational ripple, that induces further effecxts. These induce more effects, and so on. The theorists tell us that, no matter how small the effect you start with, for simple quantum gravity adding up all the effects gives an infinite answer.

Similar problems come up for other forces. For them, however, there's a fix. If you assume that, say, electromagnetism has finite effects at some distance scale then you can use something called the renormalization group to calculate how big the effects are at other distance scales. So long as you don't try to extend the calculation to distances of zero, you get sensible (and correct) results. Theorists say this technique doesn't work for gravity.

Mike W.


(published on 07/31/2013)

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