Is Spacetime a Tangible Entity or Just a Relational Concept in Physics?

[Kenny_L]

i guess we could argue this all day and there really is no answer, but your mind isn't actually a different dimension... realistically your brain has a processor and memory and obviously a bunch of other junk... but your "processor" stores the "thought" of a unicorn in your memory chemically and its the thought that exists "in reality" which is the definition of existing in the first place (reality) so the "thought" exists to represent the unicorn which itself does not exist. Infinity does not really "exist" but we can represent it and use it. Same thing with immaginary numbers.

Yes...but the thing is...how do you know if you, yourself, might be a box, hooked up to a virtual reality system, where everything you see, and 'do' are simulations? But, if the simulations are so 'real' where you, yourself, can't even tell whether you're actually a box, then there's no difference between one form of existence or another. It becomes existence...or 'real'...and even thoughts of something like a unicorn become 'real'...or existing...even if it exists 'inside' your 'head'.

 

[shamrock5585]

haha the good old theory from the matrix movie... don't you think if some living creature made up a virtual reality system there would be flaws in it and one of the 6.5 billion ppl on the planet would have experienced a side effect and figured it out or something? I mean for all our existence we have been providign answers for where we came from and how the world works and this virtual reality just happens to be perfect?

 

[robheus]

I don't think that existential philosophical questions should be discussed in the context of physics.
We are best to avoid bickering philosophy and semantics.

The context of the subforum IS however PHILOSOPHY, so why not?

 

[Evo]

The context of the subforum IS however PHILOSOPHY, so why not?

Because the science guidelines hold in this forum. If a thread wanders too far away from known science, it will be closed. This thread has already been closed once and it's not doing all that well. Let's all follow cristo's advice and limit this discussion to whether spacetime is a real entity, or a mathematical construct.

 

[robheus]

About space time existence:

In Newtonian physics, space and time are merely distance relations between objects/events.

In General Relativity though, space time posseses properties, like curvature.
Objects in space time are causing space time (more mass in one place->more curvature) and also a curved space causes objects to follow curved trajectories.

This at least shows that in GR spacetime is more intimately related to matter, and is not just "emptiness". But also it is not an ether (a fluid medium).

Spacetime does not exist apart from matter, and neither does matter exist apart from spacetime.

 

[starkind]

Just curious. What makes you think matter exists?

 

[madness]

Just saying that in GR spacetime really exists doesn't make it true. I don't see that the same old relational view of space and time can't be kept when the transition to Einstein's GR is made. Instead of saying "spacetime is curved", you could say "objects follow a curved trajectory", which I think is a more sensible conclusion to draw from the evidence. How does any of this show that spacetime is not just "emptiness"? Why does it imply that spacetime doesn't exist without matter?

 

[oldman]

Just saying that in GR spacetime really exists doesn't make it true. I don't see that the same old relational view of space and time can't be kept when the transition to Einstein's GR is made. Instead of saying "spacetime is curved", you could say "objects follow a curved trajectory", which I think is a more sensible conclusion to draw from the evidence. How does any of this show that spacetime is not just "emptiness"? Why does it imply that spacetime doesn't exist without matter?

By describing the trajectory of objects, rather than saying 'spacetime is curved' you are taking a welcome step towards an operational definition of spacetime. I strongly support such a concrete approach.

But keep in the back of your mind that spacetime is an abstract mathematical 'space'. Its metric is defined with space and time coordinates, based on the concept of number. And numbers are abstractions fundamental to mathematics. Mathematics itself is ultimately nothing more than an extraordinarily powerful language that clever folk have invented and other clever folk use to quantitatively describe nature.

In the end I believe it's simpler to detour past such complications and take an operational approach, as you have done.

 

[robheus]

Just saying that in GR spacetime really exists doesn't make it true. I don't see that the same old relational view of space and time can't be kept when the transition to Einstein's GR is made. Instead of saying "spacetime is curved", you could say "objects follow a curved trajectory", which I think is a more sensible conclusion to draw from the evidence. How does any of this show that spacetime is not just "emptiness"? Why does it imply that spacetime doesn't exist without matter?

In GR it is mass that causes spacetime curvature. But this works also the other way around in that mass is the result of curved spacetime.

The argument that spacetime is not really empty (as in Newtonian physics) because there are virtual particles in all parts of space, and as we assume also, contains dark energy.
So this makes the current viewpoint on what spacetime is different as in the Newtonian physics.

 

[oldman]

In GR it is mass that causes spacetime curvature.

Agreed.

But this works also the other way around in that mass is the result of curved spacetime.

No. Why should this be so?

 

[madness]

In GR, mass causes an object to follow a curved path. This does not mean that spacetime is some kind of physical thing which is curved. What has virtual particles and dark energy got to do with whether spacetime is real? Nobody said space was empty. Of course in GR space and time behave differently than in Newtonian physics, distances and times become shorter and longer because of mass. This does not imply that there is some kind of fabric which is distorted.

 

[shamrock5585]

keep in mind also that in Newtonian physics the math all works out perfectly for small distance and short times, relative to the universe... this is why special relativity includes spacetime. At rediculously high speeds I.E. energies and really large amounts of mass we start to see that Newtonian physics ends up being scewed by alot. what einstein did was describe spacetime as a fabric so that people could picture what it was... but can you picture a four dimensional object... spacetime isn't really a fabric or an object... but objects follow trajectories on it, and really large objects curve and shape it. By thinking of it as a slate on which everything occurs we can get the math correct when applied to physics of any scale. Its like a 3 dimensional painting which is erased and repainted every instant.

 

[madness]

I agree with everything you wrote there but I think it is important to keep in mind that the whole "fabric" view of spacetime is just a way of looking at it, and not a view demanded by the maths of the theory. It is ok to think of spacetime in this way I think it is very much an interpretation of the theory rather than a scientific fact.