- #1

- 381

- 1

## Main Question or Discussion Point

It is said that minkowksi spacetime is flat. How about galilean (newtonian) spacetime, is it flat too? If not, what is it?

It is also said that it is unknown whether there is geometry or spacetime inside planck scale. If there is none. I can't imagine how the planck scale without geometry can create the flat spacetime... although I can imagine how spin-2 field in that flat spacetime can create gravity (or curved spacetime).

According to Richard Feynman in his book "Feynman Lectures on Gravitation":

If Einstein gravity is a theory of a spin-2 field in flat space. How can you reconcile this with the conjecture that spacetime doesn't even exist in planck scale. What produce flat spacetime (or gallelian space) then from planck scale? Is there a corresponding field for flat spacetime? I just want to imagine how this occurs. Thanks

It is also said that it is unknown whether there is geometry or spacetime inside planck scale. If there is none. I can't imagine how the planck scale without geometry can create the flat spacetime... although I can imagine how spin-2 field in that flat spacetime can create gravity (or curved spacetime).

According to Richard Feynman in his book "Feynman Lectures on Gravitation":

The claim that the only sensible theory of an interacting massless spin-2 field is essentially general relativity (or is well approximated by general relativity in the limit of low energy) is still often invoked today. (For example, one argues that since superstring theory contains an interacting massless spin-2 particle, it must be a theory of gravity.) In fact, Feynman was not the very first to make such a claim."

The field equation for a free massless spin-2 field was written down by Fierz and Pauli in 1939[FiPa 39]. Thereafter, the idea of treating Einstein gravity as a theory of a spin-2 field in flat space surfaced occasionally in the literature.

If Einstein gravity is a theory of a spin-2 field in flat space. How can you reconcile this with the conjecture that spacetime doesn't even exist in planck scale. What produce flat spacetime (or gallelian space) then from planck scale? Is there a corresponding field for flat spacetime? I just want to imagine how this occurs. Thanks

Last edited: