A lot of supporters of string theory say that it has to be right because the quantum gravity is necessary for the universe, is this true? Does the universe need quantum gravity?

  • $\begingroup$ It's not clear what you're asking, perhaps you should elaborate? $\endgroup$ – Omar Nagib Jan 31 '16 at 20:42
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    $\begingroup$ Universe doesn't need anything. It works just fine. We need to understand it better. $\endgroup$ – Peter R Jan 31 '16 at 21:11
  • $\begingroup$ No, gravity does not have to be quantized, that's just a religious belief among string theorists. Eventually spacetime has to be quantized in some way, or, better, it has to reproduce quantum field theory at the low energy limit, but this has no logical consequences for gravity. Gravity could be a thermodynamic remnant force of a higher hierarchy layer. If you stare at the math long enough, that's actually what it looks like, IMHO. $\endgroup$ – CuriousOne Jan 31 '16 at 21:41
  • $\begingroup$ Possibles duplicates: physics.stackexchange.com/q/6980/2451 , physics.stackexchange.com/q/10088/2451, physics.stackexchange.com/q/52211/2451 and links therein. $\endgroup$ – Qmechanic Feb 1 '16 at 0:19