Is Space-Time a Physical Entity or a Mathematical Model?

[geordief]

I was answering a question about "physicalness", in general. Updating the "hit it with a hammer" criterion. Not specifically about spacetime.

Do you think the recent Binary Black Hole merger counts as "hitting space time (or rather whatever it is spacetime is modeling) with a hammer" ?

 

It had a physical effect didn't it?

[koti]

Do you think the recent Binary Black Hole merger counts as "hitting space time (or rather whatever it is spacetime is modeling) with a hammer" ?

 

It had a physical effect didn't it?

 

Gravity Probe B seemed to be on that track too ?

[geordief]

 

Gravity Probe B seemed to be on that track too ?

I haven't learned about frame dragging yet. That is what it was testing ,was it ?

[koti]

I haven't learned about frame dragging yet. That is what it was testing ,was it ?

Yes, the results of the frame dragging effect near the Earth were comfirmed.

[swansont]

Do you think the recent Binary Black Hole merger counts as "hitting space time (or rather whatever it is spacetime is modeling) with a hammer" ?

 

It had a physical effect didn't it?

 

 

Black holes make photons go away (and create them, too, as matter falls in). A merger is an event, rather than a physical object by itself.

[geordief]

So I can't think of it like two hands clapping or one hammer striking another anvil?

[swansont]

So I can't think of it like two hands clapping or one hammer striking another anvil?

You can, but the analogy is limited.

[geordief]

You can, but the analogy is limited.

If it was two stars colliding would the analogy be perfect?

 

Would those two stars create gravitational waves that could reasonably be considered to be "hitting spacetime (or rather whatever it is modeling) with something completely analogous to a hammer" ?

 

Would those gravitational waves be theoretically detectable in the same way as those of the BBH?

[swansont]

If it was two stars colliding would the analogy be perfect?

 

Would those two stars create gravitational waves that could reasonably be considered to be "hitting spacetime (or rather whatever it is modeling) with something completely analogous to a hammer" ?

 

Would those gravitational waves be theoretically detectable in the same way as those of the BBH?

 

 

They aren't hitting spacetime, they're hitting each other.

[koti]

 

 

They aren't hitting spacetime, they're hitting each other.

Gravity probe B confirmed the frame dragging effect which suggest to me that spacetime is indeed being "hit" Or am I mistaken?

[geordief]

 

 

They aren't hitting spacetime, they're hitting each other.

Is there anything to my pov that nothing actually "hits" anything . Everything takes place at a distance. Contact is never made when we say two objects "hit" each other.

 

Does the putative "spacetime " ** that might be said to exist as what is modeled by the spacetime model need to be physically hit if the same can be said for what we would consider to be physical objects?

 

I am not sure how coherent my argument is . Are gravitational waves considered to be physical objects?

 

 

** I would like to give it another name to distinguish it from the spacetime model. Could I call them "spacetime model " and "spacetime modeled" respectively .

 

Or does this attempt to name what spacetime is modeling seem too close to "aether" ?

[michel123456]

And everybody seems to forget that spacetime "exists" inside the objects too. The interval between the nucleus of an atom and the electrons is spacetime too.

[swansont]

Gravity probe B confirmed the frame dragging effect which suggest to me that spacetime is indeed being "hit" Or am I mistaken?

 

 

I'm unaware of anything related to gravity probe B that would count as "hitting" anything. It confirmed effects of the curved geometry used to describe gravity.

Is there anything to my pov that nothing actually "hits" anything . Everything takes place at a distance. Contact is never made when we say two objects "hit" each other.

 

Does the putative "spacetime " ** that might be said to exist as what is modeled by the spacetime model need to be physically hit if the same can be said for what we would consider to be physical objects?

 

I am not sure how coherent my argument is . Are gravitational waves considered to be physical objects?

 

 

** I would like to give it another name to distinguish it from the spacetime model. Could I call them "spacetime model " and "spacetime modeled" respectively .

 

Or does this attempt to name what spacetime is modeling seem too close to "aether" ?

 

We got rid of the aether — an actual physical medium — because a physical medium isn't compatible with relativity. So you can't replace it with another one. Neither light nor gravity requires a medium.

 

If we ever come up with a quantum theory of gravity, the exchange particle will be a graviton. Anything explained with spacetime distortion will have an alternate explanation that relies on the graviton, much like classical EM wave explanations give way to photon explanations.

 

How will spacetime be considered a physical thing when it's no longer part of the model?

[StringJunky]

If we ever come up with a quantum theory of gravity, the exchange particle will be a graviton. Anything explained with spacetime distortion will have an alternate explanation that relies on the graviton, much like classical EM wave explanations give way to photon explanations.

 

How will spacetime be considered a physical thing when it's no longer part of the model?

I think this just shows that spacetime is not real; it's a model. Spacetime will go the way of phlogiston.

[koti]

 

 

I'm unaware of anything related to gravity probe B that would count as "hitting" anything. It confirmed effects of the curved geometry used to describe gravity.

 

I know I'm doing a little circle here but if spacetime curves due to mass that counts as gravity "hitting" spacetime to me. There was a doubt a few posts earlier that a human can't be called an entity. I do not share this doubt, I think its a straight path to go full nutts.

 

If we ever come up with a quantum theory of gravity, the exchange particle will be a graviton. Anything explained with spacetime distortion will have an alternate explanation that relies on the graviton, much like classical EM wave explanations give way to photon explanations.

 

I wish I shared your confidence on the look of theory of quantum gravity. Unfortunately I am helpless here.

 

How will spacetime be considered a physical thing when it's no longer part of the model?

As above.

I think this just shows that spacetime is not real; it's a model. Spacetime will go the way of phlogiston.

 

That might be possible.

Edited August 26, 2016 by koti

[swansont]

Spacetime will go the way of phlogiston.

I don't think so. Phlogiston was fundamentally flawed; it actually did predict a real substance, which doesn't exist. Spacetime stems from a classical model that is incomplete, similar to E&M, the classical parts of which have not gone away.

I know I'm doing a little circle here but if spacetime curves due to mass that counts as gravity "hitting" spacetime to me. There was a doubt a few posts earlier that a human can be called an entity. I do not share this doubt, I think its a straight path to go full nutts.

 

Gravity stems from spacetime curvature. You are saying spacetime curvature hits spacetime.

[koti]

Gravity stems from spacetime curvature. You are saying spacetime curvature hits spacetime.

 

"Gravity stems from spacetime" is this undoubtedly true?

Spacetime curvature stems from gravity - is this undoubtedly false ?

You are right, I'm getting mixed up here.

 

I had to edit "can" to can't in my previous post.

[geordief]

We got rid of the aether — an actual physical medium — because a physical medium isn't compatible with relativity. So you can't replace it with another one. Neither light nor gravity requires a medium.

 

If we ever come up with a quantum theory of gravity, the exchange particle will be a graviton. Anything explained with spacetime distortion will have an alternate explanation that relies on the graviton, much like classical EM wave explanations give way to photon explanations.

 

How will spacetime be considered a physical thing when it's no longer part of the model?

 

I realize this is not how you might frame the question but if I refer to spacetime as a model does the term (in that context) "the modeled" have any meaning (apart from a semantic one) ?

 

Do we (can we) have a model without a "modeled"?

 

Or do we have a "modeled" that bears no apparent or intuitive resemblance to the model save in that the model allows us to predict events in the said "modeled" ?

Edited August 26, 2016 by geordief

[StringJunky]

I don't think so. Phlogiston was fundamentally flawed; it actually did predict a real substance, which doesn't exist. Spacetime stems from a classical model that is incomplete, similar to E&M, the classical parts of which have not gone away.

 

Gravity stems from spacetime curvature. You are saying spacetime curvature hits spacetime.

I meant it loosely; it sounded good in my mind.

[koti]

Gravity stems from spacetime curvature.

Spacetime with zero mass "in it" is flat and there is no gravity in that scenario. Spacetime with mass "in it" curves and there is gravity present in that scenario. If this is correct how can gravity stem from spacetime curvature, isnt it the other way around?

[studiot]

 

I realize this is not how you might frame the question but if I refer to spacetime as a model does the term (in that context) "the modeled" have any meaning (apart from a semantic one) ?

 

Do we (can we) have a model without a "modeled"?

 

Or do we have a "modeled" that bears no apparent or intuitive resemblance to the model save in that the model allows us to predict events in the said "modeled" ?

 

Now you are thinking straight and asking sensible questions. +1

[koti]

I just realized how incredibly dumb my 2 previous comments are. I will leave them to remind me what happens when I do 10 things at once.

[swansont]

Spacetime with zero mass "in it" is flat and there is no gravity in that scenario. Spacetime with mass "in it" curves and there is gravity present in that scenario. If this is correct how can gravity stem from spacetime curvature, isnt it the other way around?

 

 

 

Gravity is spacetime curvature. You can't have one without the other. If space is curved, then the path followed is that which we would perceive as an acceleration of gravity. One is Newton and the other is Einstein.

 

I realize this is not how you might frame the question but if I refer to spacetime as a model does the term (in that context) "the modeled" have any meaning (apart from a semantic one) ?

 

Do we (can we) have a model without a "modeled"?

 

Or do we have a "modeled" that bears no apparent or intuitive resemblance to the model save in that the model allows us to predict events in the said "modeled" ?

 

Behavior is modeled in physics. Position, speed, acceleration, energy, momentum, etc. — all observable in some way.

[koti]

 

 

 

Gravity is spacetime curvature. You can't have one without the other. If space is curved, then the path followed is that which we would perceive as an acceleration of gravity. One is Newton and the other is Einstein.

 

 

Right. Thank you for explaining. As I mentioned above, I've had a temporal epsiode of twisting concepts around :/

[geordief]

 

Behavior is modeled in physics. Position, speed, acceleration, energy, momentum, etc. — all observable in some way.

So ,to use my terminology the "modeled" is not so much a thing as a set of events of differing properties?

 

Can we talk of an event having a property?

 

If not what do "Position, speed, acceleration, energy, momentum" describe?

 

Relationships between events?