Quote from Rovelli's book, page 19:(adsbygoogle = window.adsbygoogle || []).push({});

"In classical general relativity...there is no preferred time variable...[but] we nevertheless have a notion of spacetime for each given solution. [By contrast] in quantum theory there are no trajectories. Thus, THERE IS NO PHYSICAL SPACETIME IN QUANTUM GRAVITY...."

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

This is the most interesting book of philosophy I can remember seeing in several decades

(also a book ofnaturalphilosophy, that is to say, physics)

The online draft of Rovelli's "Quantum Gravity" to be published by Cambridge U. Press

space IS the gravitational field----things move, rotate, accelerate with reference to the gravitational field

time has no physical existence---analogous to the fact that an electron has no real trajectory: the sum over possible trajectories gives the transition amplitude between here and there

time is a property of a classical solution of the GR field----a "trajectory" of geometrical states----but this is only a classical (non-quantum) approximations

there are only transition amplitudes between states of the 3D geometry----development along a classical trajectory does not correspond to physical reality

clocks (whether mechanical, electronic, astronomical) are real physical systems that we distinguish from other systems by convention---they evolve according to sum-over-paths transition amplitudes along with everything else---thus observed states of the world can include readings on various clocks but there is no physical time axis

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Spacetime has no physical existence

**Physics Forums | Science Articles, Homework Help, Discussion**