Questions about space and matter

[Twinduck]

TL;DR Summary

Does matter "create" space?

I have a question that I have been unable to find an answer to.

The question is does matter "create" space?

Some places I read that space "just is", and matter fills it and creates its gravitational curving. But that something "just is" is supremely unsatisfying as far as answers go.
Another take I've read is that the concept of space doesn't really have any meaning outside of gravitational fields, though I have been unable to find more details.

So if some matter was to spontaneously manifest somewhere there were no gravitational fields, or no space, would it evoke the space it needed to exist in?
Another way to ask is is space an attribute of matter, or is it just something matter can occupy and shape? Intuitively I am inclined to think the former.

 

[PeterDonis]

Some places I read

Another take I've read

Where? Please give specific references.

 

[PeterDonis]

if some matter was to spontaneously manifest somewhere

It can't. This would violate the laws of physics.

is space an attribute of matter, or is it just something matter can occupy and shape?

What's the difference?

Remember that in relativity, the fundamental invariant geometric object is spacetime, not "space".

 

[Twinduck]

Where? Please give specific references.

https://einstein.stanford.edu/conte... us that,that creates the gravitational field.

This seems to say that space cannot exist independently of matter, which seems to fit with the notion that matter "evokes" space. But it does not say that it does, it merely does not rule out the possibility.

https://www.quora.com/Can-matter-create-time-and-space

I would say this link is less reliable, since I do not know who made the reply to the question.

 

[Twinduck]

It can't. This would violate the laws of physics.


What's the difference?

Remember that in relativity, the fundamental invariant geometric object is spacetime, not "space".

The part about matter spontaneously manifesting was a hypothetical, of course. I just didn't want to involve the whole big bang scenario just yet.

The difference between space "just existing" and space being an attribute of matter is pretty significant, I'd say. It seems to me that if matter "evokes" space there should be a correlation between the size of the universe and the stuff in it.

 

[PeterDonis]

I would say this link is less reliable

The second is less reliable than the first, yes, but neither of them are good sources for learning actual physics. You need to be looking at actual textbooks.

The part about matter spontaneously manifesting was a hypothetical

A useless one, because the only tool we have to analyze hypotheticals about physics is the laws of physics, so a hypothetical that violates them means we can't use anything at all. Any answer you give is just making something up with no basis.

I just didn't want to involve the whole big bang scenario just yet.

You don't need to. The basic issue is what I've already described: you are talking about "space" instead of spacetime.

The difference between space "just existing" and space being an attribute of matter is pretty significant, I'd say. It seems to me that if matter "evokes" space there should be a correlation between the size of the universe and the stuff in it.

Why? What law of physics tells you this?

(Hint: there isn't one. As you will see if you look at textbooks.)

 

[PeterDonis]

Two good textbooks that are available for free online are Taylor & Wheeler's Spacetime Physics and Sean Carroll's online lecture notes:

https://phys.libretexts.org/Bookshelves/Relativity/Spacetime_Physics_(Taylor_and_Wheeler)

https://arxiv.org/abs/gr-qc/9712019

 

[Ibix]

This seems to say that space cannot exist independently of matter, which seems to fit with the notion that matter "evokes" space.

I'm not quite sure what experiments he's talking about. You can certainly describe empty space within the framework of relativity - that's what special relativity is. And there are a lot of solutions to Einstein's field equations that are vacuum solutions throughout most of spacetime.

The difference between space "just existing" and space being an attribute of matter is pretty significant, I'd say.

The problem with this kind of statement is that you are not making any testable claims. You think the difference is significant - ok - what measurement can I make that will give me a different result if one or the other thing is true?

 

[renormalize]

https://einstein.stanford.edu/content/relativity/a11332.html#:~:text=General relativity tells us that,that creates the gravitational field.

Quoting from that link:
"Can space exist by itself without matter or energy around?
No. Experiments continue to show that there is no 'space' that stands apart from space-time itself...no arena in which matter, energy and gravity operate which is not affected by matter, energy and gravity. General relativity tells us that what we call space is just another feature of the gravitational field of the universe, so space and space-time can and do not exist apart from the matter and energy that creates the gravitational field. This is not speculation, but sound observation.
All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program."
This statement implies that flat empty spacetime cannot exist, even in theory. I wish Dr. Sten Odenwald provided some actual references to these "experiments" and "sound observations" to support this.

 

[PeterDonis]

there are a lot of solutions to Einstein's field equations that are vacuum solutions throughout most of spacetime.

Or even all of it, without being flat spacetime--for example the vacuum black hole solutions.

 

[Twinduck]

what measurement can I make that will give me a different result if one or the other thing is true?

As far as I know, there are estimates on the size of space that are made by measuring waves in the CMB.
There are also estimates of how much matter exists in the universe.
If we knew the amount of gravity all that mass produces, as well as how big the combined gravitational field would be, someone way more skilled in maths than me should be able to calculate how big the universe should be based on how much matter/gravity there is.

If that calculation yielded a number similar to methods already used, wouldn't that tell us something?

 

[Ibix]

As far as I know, there are estimates on the size of space that are made by measuring waves in the CMB.

And the best estimate is "infinite in extent".

how big the combined gravitational field would be,

The gravitational field of even a pebble extends to infinity.

 

[Twinduck]

You don't need to. The basic issue is what I've already described: you are talking about "space" instead of spacetime.


Why? What law of physics tells you this?

It is logical. If the term space, or spacetime, since you insist on accurate nomenclature, has no meaning outside of gravitational fields, and any material object creates a gravitational field that is directly related to its mass, there cannot be more spacetime than what the combined matter of the whole universe can create.

If, however, there is no correlation between the size of the universe and all things in it, all this goes out the window, of course.

 

[PeterDonis]

As far as I know, there are estimates on the size of space that are made by measuring waves in the CMB.

Please give a reference.

There are also estimates of how much matter exists in the universe.

There are estimates of the density of matter. But that is not the same as "how much". Our best current model says the universe is spatially infinite.

If we knew the amount of gravity all that mass produces, as well as how big the combined gravitational field would be, someone way more skilled in maths than me should be able to calculate how big the universe should be based on how much matter/gravity there is.

Again, you need to look at whether there are any laws of physics that tell you this, instead of just waving your hands. (And, as I have already told you, if you look you won't find any, because there aren't any.)

 

[PeterDonis]

It is logical.

Logic has to start from some premises. If you start from false premises, no amount of logic will help you. You need to learn the correct premises to start from.

If the term space, or spacetime, since you insist on accurate nomenclature, has no meaning outside of gravitational fields

I said no such thing. Please stop speculating based on what you currently think you know, which appears to be entirely wrong, and go learn the correct physics from a textbook. Please note that personal speculation is off limits here.

 

[PeterDonis]

there is no correlation between the size of the universe and all things in it

In your current state of knowledge, yes, this is the best way for you to look at it--the quoted statement is indeed true, and all your logic up to now goes out the window. But that's still a very limited viewpoint; you will learn a lot more, and will have a much better basis for reasoning further, if you take the time to work through a textbook.

 

[Twinduck]

In your current state of knowledge, yes, this is the best way for you to look at it

All right. A simple answer. It still does not answer the main question though. Is spacetime an attribute of matter?

As someone told me further up, even the gravitational field of a pebble is infinite. So even if "spacetime was an attribute of matter" there would be no correlation between the size of the universe and all things in it.

 

[PeterDonis]

Is spacetime an attribute of matter?

The question is not well posed and has no answer.

If you want to try to find a question that is well posed, the advice @Ibix already gave you is a good start: think of what experiments you could do that would give different results depending on what the answer to the question was.

 

[PeterDonis]

even the gravitational field of a pebble is infinite.

A better way to put this would be, even a spacetime that only contains one pebble, with no other matter anywhere, is still infinite in extent and has nonzero curvature everywhere. The term "gravitational field" is ambiguous, and is not a fundamental thing in relativity anyway.

 

[Twinduck]

The question is not well posed and has no answer.

Of course it has an answer. It is a simple question. Does spacetime exist even with no mass in it? If so, how would you even know, if the only way we can perceive spacetime is by how it affects matter and energy within it?
And can there be mass without spacetime?
Is there a relationship between matter and spacetime beyond how gravitational fields curve it?

Do we, the human race, have an answer to how spacetime came to exist, or what causes it?

If I were to assert that spacetime is an attribute of matter, would it violate any laws of physics? Are there any laws of physics that preclude this eventuality?
If so, I would really really like to know.

 

[Ibix]

Of course it has an answer. It is a simple question.

There are a lot of simple questions that are not well posed so they have no answer. What colour is an object that is both green and red? The premises of that question are contradictory so it has no answer, but it's really simple. Questions like "is spacetime an attribute of matter" are unanswerable if you can't state a measurable consequence of the answer being yes or no. The only "measurable" consequences you've proposed aren't measurable and don't really make sense. Your question therefore remains unanswerable.

Does spacetime exist even with no mass in it?

Again: how could you know? We can write down mathematics describing an empty universe, but our universe is not like that. Does that mean it exists, or that it can exist? How can you tell?

 

[Vanadium 50]

since you insist on accurate nomenclature

Peter is right to. Otherwise the gribblebazz blorbitz will be too deculareous.

 

[Mister T]

Some places I read that space "just is", and matter fills it and creates its gravitational curving. But that something "just is" is supremely unsatisfying as far as answers go.

Well, you could also say that matter "just is".

 

[strangerep]

Is spacetime an attribute of matter?

Short answer: "no".

For a longer answer, read up on the distinction between "intrinsic" and "extrinsic" properties.

 

[Dale]

It seems to me that if matter "evokes" space there should be a correlation between the size of the universe and the stuff in it.

Then observations indicate that matter does not “evoke” space.

It still does not answer the main question though. Is spacetime an attribute of matter?

A scientific question is one that can be answered through the scientific method. So you need an experiment whose outcome depends on the answer.

What experiment could be performed whose outcome depends on whether or not spacetime is an attribute of matter? What is the experimental setup and what measurements will be performed? Which numerical values for the measurement would indicate a “yes” and which values would indicate a “no”?

 

[Twinduck]

There are a lot of simple questions that are not well posed so they have no answer. What colour is an object that is both green and red? The premises of that question are contradictory so it has no answer

There is no contradiction in your question. A lot of things are both green and red. I suspect you mean an object that is all one color, and that color is simultaneously green and red. Never mind the answer to that one. The question itself doesn't make sense.

I take your point, though. I disagree that the question "is space an attribute of matter" is in itself poorly posed.
But I do agree that it is poorly posed in relation to our capacity to find the answer, as you guys pointed out to me.

 

[Twinduck]

Got some new responses since last night. Nice.

Thanks everyone for your input.

When I was a kid I started learning to play the guitar. I did it by trial and error, without anyone to teach me. Not that there weren't people around who could do that. I just wasn't suceptible to it. I have played guitar for over 40 years now, and my unconventional learning path has been both a blessing and a curse. I spent many years practicing to get rid of bad habits and mistakes I'd taught myself along the way.

I mention this because I started learning about physics and relativity the same way. I'd say the negative effects of that are readily apparent in this thread. My dabbling in these subjects is a solo endeavor for me, as no one around me shares that interest. Inside my little echo chamber I am god. But if I stay there too long I run the risk of the earth becoming flat.
This was exactly what I needed. Thanks!

 

[PeroK]

I take your point, though. I disagree that the question "is space an attribute of matter" is in itself poorly posed.

What is the definition of "attribute" in this context?

 

[Twinduck]

What is the definition of "attribute" in this context?

Feature, perhaps? Maybe "effect of" or "consequence of".

My first wording was "does matter create space".
Second was "is space an attribute of matter."

Others in this thread have made me aware that the question is poorly posed, since there is no observation or experiment we can perform to find the answer.

 

[Dale]

I disagree that the question "is space an attribute of matter" is in itself poorly posed.
But I do agree that it is poorly posed in relation to our capacity to find the answer, as you guys pointed out to me.

In science the goal is to get answers to our questions from the universe itself. But the universe doesn’t speak English. So we have to pose the question in the form of an experiment.

 

[Histspec]

Another way to ask is is space an attribute of matter, or is it just something matter can occupy and shape? Intuitively I am inclined to think the former.

This is somehow related to Mach's principle (at least in Einstein's reading): Are all forms of gravitational fields, the spacetime metric, and the inertia of bodies, fully determined by the masses of the universe? A nice historical description of this problem was given by Janssen:
https://philsci-archive.pitt.edu/4377/
See particular section 5. Fourth attempt: Mach’s principle and cosmological constant.

Einstein initially hoped that Mach's principle holds in GR, but it was soon showed by DeSitter that GR allows for a solution with vanishing matter density, while at the same time a single test body retains its inertia. Einstein was not convinced, so he wrote to DeSitter in 1917:

It would be unsatisfactory, in my opinion, if a world without matter were possible. Rather, it should be the case that the $g_{\mu\nu}$ -field is fully determined by matter and cannot exist without the latter. This is the core of what I mean by the requirement of the relativity of inertia.

Anyway, there was nothing wrong with DeSitter's solution, which led Einstein (among other reasons) to abandon Mach's principle, so he wrote in 1954:

In my view one should no longer speak of Mach’s principle at all. It dates back to the time in which one thought that the “ponderable bodies” are the only physically real entities and that all elements of the theory which are not completely determined by them should be avoided. (I am well aware of the fact that I myself was long influenced by this idée fixe)

 

[PeterDonis]

it was soon showed by DeSitter that GR allows for a solution with vanishing matter density, while at the same time a single test body retains its inertia

De Sitter didn't have to show that: flat Minkowski spacetime is also such a solution. (So is Schwarzschild's vacuum solution, which was published in 1916, the first solution to be discovered, but nobody understood that at the time--this solution was only thought to be valid for the spacetime surrounding an ordinary non-rotating planet or star, and the fact that it can also describe a black hole was not realized for another two decades.)

What de Sitter showed (that Einstein didn't expect) was that adding the cosmological constant to the field equations still allowed solutions with nonzero spacetime curvature but no matter, in which test bodies retain inertia. Einstein had hoped that would not be the case, as Janssen remarks in the paper you reference.

 

[Tomas Vencl]

…….

The question is does matter "create" space(time)?….

I think that solving this guestion honestly is behind relativity framework, and needs deeper quantum gravity theory. For example:
https://en.wikipedia.org/wiki/Causal_dynamical_triangulation

 

[Histspec]

What de Sitter showed (that Einstein didn't expect) was that adding the cosmological constant to the field equations still allowed solutions with nonzero spacetime curvature but no matter, in which test bodies retain inertia. Einstein had hoped that would not be the case, as Janssen remarks in the paper you reference.

Yes, I should have added that DeSitter's vacuum solution is related to Einstein's modified field equations that include the cosmological constant. Anyway, the point is that GR solutions such as this contributed, at least in the long term, to Einstein's abandonment of his idea quoted above (inspired by Mach's principle), that the possibility of a world without matter is unsatisfactory and that the $g_{\mu\nu}$-field cannot exist without matter....

 

[PeterDonis]

GR solutions such as this contributed, at least in the long term, to Einstein's abandonment of his idea quoted above (inspired by Mach's principle), that the possibility of a world without matter is unsatisfactory and that the $g_{\mu\nu}$-field cannot exist without matter....

Yes, agreed.