What does it mean to say space and time are fundamental in physics?

[Newton-reborn]

What feature of the equations of classical physics show that space and time are fundamental and how would the equations differ if space and time were not fundamental but emergent? I heard all of this from a previous talk and I would appreciate any help and any further reading recommendations.

 

[ZapperZ]

What feature of the equations of classical physics show that space and time are fundamental and how would the equations differ if space and time were not fundamental but emergent? I heard all of this from a previous talk and I would appreciate any help and any further reading recommendations.

This is rather vague and verging on philosophy.

Here's something you might want to try and do. Try to describe, using the most minimal set of parameters, the equation of motion of anything. You may try this with classical mechanics (i.e. set up the force equation, or using a Lagrangian/Hamiltonian) or using QM via the Hamiltonian/Schrödinger equation. Do you think you can make an accurate and complete description of the dynamics without invoking spatial and temporal coordinates at all?

Zz.

 

[Newton-reborn]

It happens to be a topic in the frontiers of physics (Quantum Gravity). Nima Arkani speaks of it very often. He says that space and time cannot be fundamental because when you invoke QM the whole concept falls apart and can only be an approximation of a deeper concept. Has nothing to with philosophy

 

[PeroK]

It happens to be a topic in the frontiers of physics (Quantum Gravity). Nima Arkani speaks of it very often. He says that space and time cannot be fundamental because when you invoke QM the whole concept falls apart and can only be an approximation of a deeper concept. Has nothing to with philosophy

What is fundamental in place of spacetime?

 

[phinds]

What does it mean to say space and time are fundamental in physics?

To me it means that whoever said it does not understand cosmology. I think that neither space nor time are fundamental, they are just constituents of spacetime which IS fundamental.

 

[PeroK]

It happens to be a topic in the frontiers of physics (Quantum Gravity). Nima Arkani speaks of it very often. He says that space and time cannot be fundamental because when you invoke QM the whole concept falls apart and can only be an approximation of a deeper concept. Has nothing to with philosophy

Perhaps you could say more about what you know about the subject. For example, in what way does the whole concept of spacetime fall apart when you invoke QM? I'm wondering if this is simply the incompatibility between GR and QM? - and, the assumption that probably it's GR that will eventually be shown to emerge from a theory of quantum gravity?

Also, why would this affect classical physics? Classical physics has no need to incorporate relativity or QM. It won't need to be modified to reflect a possible future theory of emergent spacetime.

 

[ZapperZ]

It happens to be a topic in the frontiers of physics (Quantum Gravity). Nima Arkani speaks of it very often. He says that space and time cannot be fundamental because when you invoke QM the whole concept falls apart and can only be an approximation of a deeper concept. Has nothing to with philosophy

But that IS philosophy because "a deeper concept" than space-time is a speculation that has no empirical support! That's like Einstein thinking that there are "hidden variables" in QM that underlies its "probabilistic" nature. We haven't found any after all these years.

Zz.

 

[Nugatory]

What does it mean to say space and time are fundamental in physics?

That's a sufficiently vague statement that it probably means pretty much whatever the listener hears and the speaker intends it to mean. It's certainly not a rigorous statement about physics, even if it came from a professional physicist thinking about the possible future of the discipline.
When I hear it, I think about how we can accept time as "what a clock measures" and distance as "what a ruler measures" (these are Einstein's insights here) and proceed to build all of current physics on top of these concepts without needing anything deeper - but that's just me.

and how would the equations differ if space and time were not fundamental but emergent?

We won't know unless and until we find these hypothetical new equations of a hypothetical new theory in which space and time are emergent. And even then all of our current equations, which describe our universe in terms of these quantities, will remain valid.

I heard all of this from a previous talk and I would appreciate any help and any further reading recommendations.

It's a lot of work, and maybe not what you want to hear, but the best thing you can do is to acquire a solid (undergraduate physics BA degree) understanding of classical mechanics, special relativity, and quantum mechanics. That will give you enough background to at least follow along when people are talking about quantum field theory. It's really somewhat amazingly good news that a few years of serious study will get you to where you can understand something that has been built over many centuries by some of the smartest people who ever lived.