# Space-time

Status
Not open for further replies.
5

#### 5hot6un

##### Guest
Mass warps space-time. So what happens to space-time in the absence of mass?

5

#### 5hot6un

##### Guest
Because warping implies that space-time has some type of elasticity. An object like our sun moves through space-time. But there is no warped "trail" left behind. If space-time has an elastic like property, what is the force behind it? What force un-warps it? What would a completely mass free section of space-time be like? Does such a place exist? Is there any chance this is the source of dark energy?

C

#### centsworth_II

##### Guest
Virtual particles are continuously popping into and out of existence everywhere in the universe. All this activity continually warps space time at the smallest of scales. This is the quantum foam. So there is no area of space time that is not being continuously warped at some scale.

5

#### 5hot6un

##### Guest
Thank you centsworth_II

But the question remains; what force acts as the elasticity of space-time?

C

#### centsworth_II

##### Guest
5hot6un":3qkhy2jk said:
...what force acts as the elasticity of space-time?
Space-time is deformed by the presence of gravitational or electromagnetic forces. I don't know if it's right to say that the elasticity itself is a force, it's more of a property.

Of course no one knows what space-time actually is. All we have are mathematical models that describe its behavior. It may be that space-time has no physical reality and it is just a mathematical tool we use to understand the interactions between forces in the universe.

R

#### ramparts

##### Guest
Spacetime doesn't have "elasticity" - you're stretching the analogy way too far. Words like "warping" are terms used to explain relatively complicated concepts to the general public, not exact scientific definitions.

F

#### FlatEarth

##### Guest
We know space is warped by a singularity to the point that it becomes folded upon itself. QED says that virtual particles appear in empty space. They blink in and out of existence and are said to be borrowed from the future, whatever that means. :? Protons are mostly empty space, and virtual particles in that space account for 90% of a proton's mass. Using that information, then it seems that space itself must have mass. Perhaps this explains why space is warped in a gravity field. Take this a step further, and you can postulate that space can actually be compressed, and perhaps this is what happens to space in a singularity. Maybe in an area with a large collection of massive objects, like a galaxy, space is somewhat compressed, making the overall density of space higher than in an area where no matter is present. If that's true, and if space actually has mass, then perhaps this higher density space contributes to the mass of galaxies. I believe for this to be true, gravity has to work at the quantum level, which is why (I think) they are looking for carrier particles associated with gravity. :?:

I am just using bits of information that I've picked up from a few videos on the subject, and I realize that I could be way off base, but it seems plausible to me. If you have a different understanding, I'd like to hear your thoughts.

Here's a lecture that deals with the subject of virtual particles in space at the 20:00 mark. It lasts about an hour, but I'd highly recommend watching the whole thing.

5

#### 5hot6un

##### Guest
ramparts":1fnkuezk said:
Spacetime doesn't have "elasticity" - you're stretching the analogy way too far. Words like "warping" are terms used to explain relatively complicated concepts to the general public, not exact scientific definitions.
Really? My understanding is that the deformation of space-time is how gravity acts at a distance. This is supposed to be one of the most profound things that Einstein proposed. This concept moved us beyond Newton's explanations of gravity. It eliminates the need for a "graviton" particle and preserves the speed limit of particles to the speed of light. Space-time deforms in the presence of mass. Observations of gravitational lensing have confirmed this.

It sounds like a lot more than a nifty way to explain stuff to us common folk.

And since we know ST deforms, we also know it exists in a non deformed state. Right?

Therefore it would seem correct to state that ST had a tendency to be non deformed in the absence of mass.
If it did not, we would see deformed ST all over the universe where massive objects have once been.

So how far in the opposite direction from "deformed" does ST go? To continue the fabric analogy; does ST move more towards a loose mesh in the absence of matter? Or is there a pervasive steady state?

If ST does "loosen" the further away from mass it is, could this be a source of inflation?

Surely someone smarter than me must have wondered this.

C

#### centsworth_II

##### Guest
5hot6un":mk87p670 said:
... My understanding is that the deformation of space-time is how gravity acts at a distance. This is supposed to be one of the most profound things that Einstein proposed. This concept moved us beyond Newton's explanations of gravity. It eliminates the need for a "graviton" particle...
The paths of moving objects are curved by the presence of mass. It is convenient to see this as a curving of space-time. But it could also be seen as a direct action (possibly by interaction with gravitons) on a object which curves its path.

No one knows if gravitons exist or not. Being able to explain things without them does not prove they do not exist. Space-time and its deformation is a way of mathematically describing observations. That does not prove the fundamental reality of what underlies the observations. This remains unknown.

J

#### Jerromy

##### Guest
I can certainly understand the analogy which is commonly displayed as a funnel on a graph of 2D space where the massive object resides in the bottom of the funnel. In my modest oppinion that is merely demonstrating the concept that gravity pulls stronger the closer you get to the massive object, hence the funnel is pictured as a slight grade at a distance and quickly becomes a much steeper grade within the threshold proportionate to the mass of the object. It in no way demonstrates the means with which gravity acts in four dimensions but rather makes visualization of time and two dimensions easily understandable, as in rolling a marble towards the funnel one can see how the marble accelerates as it approaches and curves depending on the angle of approach. Attempting to extend that visualization to a three dimensional perspective distorts reality... for example gravitational lensing where light is the marble "grazing" the edge of the funnel, the light is not confined to a two dimensional plane where it approaches on a certain plane and exits the gravitational field on a skew of the original trajectory.

Since it is to my understanding that gravity acts on mass "to infinity and beyond" the only way space could be perfectly flat would be in a universe devoid of all mass, for visualization the sheet of fabric would be deformed at the edges no matter how big the sheet or how small the mass deforming it.

It is common scientific knowledge that space between attracted masses exhibits angular momentum as they revolve faster while they approach preserving the energy contained in the system. This is yet another example that the two dimensional funnel analogy lacks the proper visualization of reality which is observed and understood.

W

#### weeman

##### Guest
Thanks for posting that vid, FlatEarth! Very good stuff. I just watched the whole thing at 1 o'clock in the morning :mrgreen:

U

#### undidly

##### Guest
The funnel is real.
The gradient at any point is the escape velocity at that point,divided by C ,multiplied by 90 degrees.

Try the limits.

Zero mass should calculate to zero gradient.
Zero mass has zero escape velocity.
Zero /C *90 degrees = zero gradient ,flat .

A black hole should have the maximum gradient.
A black hole escape velocity is C (at the event horizon).
C/C * 90 degrees = 90 degrees ,straight down.

Earth is between these limits,less than a twentieth of a degree at the surface.Work it out.
The depth of the funnel (G well) for Earth is less than a metre.

This is GR stuff.There are no gravitons.

5

#### 5hot6un

##### Guest
undidly":1ougs8uh said:
The funnel is real.
The gradient at any point is the escape velocity at that point,divided by C ,multiplied by 90 degrees.

Try the limits.

Zero mass should calculate to zero gradient.
Zero mass has zero escape velocity.
Zero /C *90 degrees = zero gradient ,flat .

A black hole should have the maximum gradient.
A black hole escape velocity is C (at the event horizon).
C/C * 90 degrees = 90 degrees ,straight down.

Earth is between these limits,less than a twentieth of a degree at the surface.Work it out.
The depth of the funnel (G well) for Earth is less than a metre.

This is GR stuff.There are no gravitons.
Thanks undidly!

These simple equations state quite clearly (to me at least) that ST is elastic-like. Now I need someone with a deep understanding of GT to explain how ST's tenancy to be flat in the absence of matter affects the universe.

Let me try to say this in a different way.
ST alone is flat. Add mass and ST warps. Take mass away, ST flattens back out. This tendency to move towards flat is a force and MUST have some influence on the universe as a whole. Maybe it is known and accounted for. I would like to know how.

F

#### FlatEarth

##### Guest
weeman":3r5rmfkm said:
Thanks for posting that vid, FlatEarth! Very good stuff. I just watched the whole thing at 1 o'clock in the morning :mrgreen:
Hi weeman. Credit must go to Jeters_boy, who posted it in another thread. I plan to watch it again, I liked it that much. I'm afraid I'm drawing incorrect conclusions from this lecture that was intended for laymen like me. Oh well. I have no plans to go back to college to study it!

U

#### undidly

##### Guest
5hot6un":29kautgp said:
undidly":29kautgp said:
The funnel is real.

These simple equations state quite clearly (to me at least) that ST is elastic-like. Now I need someone with a deep understanding of GT to explain how ST's tenancy to be flat in the absence of matter affects the universe.

Let me try to say this in a different way.
ST alone is flat. Add mass and ST warps. Take mass away, ST flattens back out. This tendency to move towards flat is a force and MUST have some influence on the universe as a whole. Maybe it is known and accounted for. I would like to know how.
Why does ST spring back to flat?.
Because it is under tension.
Whatever is causing the universe to expand is stretching ST.

How fast does it spring back?.
Depends on the tension and the inertia of ST.These determine the speed of gravitational waves.
If a large mass ceases to exist then ST will spring back but does it overshoot a little so the G well becomes a G hill?.
Spring back like a drum skin and overshoot then back.Up down up down a few cycles.Makes the note(frequency)
of a drum.
Up down up down in ST gives the frequency (note)of the Gravitational waves.

We can't make a mass cease to exist so we have to look at other disturbances like orbiting star pairs.
No gravitational waves detected yet but the explanation is not for this topic.

J

#### Jerromy

##### Guest
"Waves" implies a variance in a field. If there were some type of waves to the force of gravity I'm sure we'd have figured it out by now. Newton may not have had the insight but Einstien did and he determined that gravity is a field, not a "wave of gravitons".

5

#### 5hot6un

##### Guest
Jerromy":169uyp50 said:
"Waves" implies a variance in a field. If there were some type of waves to the force of gravity I'm sure we'd have figured it out by now. Newton may not have had the insight but Einstien did and he determined that gravity is a field, not a "wave of gravitons".
Einstein's GT does not say gravity is a field. Newton suggested that. Einstein explained that gravity is the deformation of space-time.

That's kind of the point of this tread. Einstein's deformed ST implies it is a medium.

There is an active search for gravity waves.
http://www.spacedaily.com/news/gravity-05f.html

The term gravity waves is wrong in my opinion. They are space-time waves. Ripples in the ST medium.

R

#### ramparts

##### Guest
5hot6un":2b73y0ui said:
ramparts":2b73y0ui said:
Spacetime doesn't have "elasticity" - you're stretching the analogy way too far. Words like "warping" are terms used to explain relatively complicated concepts to the general public, not exact scientific definitions.
Really? My understanding is that the deformation of space-time is how gravity acts at a distance. This is supposed to be one of the most profound things that Einstein proposed. This concept moved us beyond Newton's explanations of gravity. It eliminates the need for a "graviton" particle and preserves the speed limit of particles to the speed of light. Space-time deforms in the presence of mass. Observations of gravitational lensing have confirmed this.

It sounds like a lot more than a nifty way to explain stuff to us common folk.

And since we know ST deforms, we also know it exists in a non deformed state. Right?

Therefore it would seem correct to state that ST had a tendency to be non deformed in the absence of mass.
If it did not, we would see deformed ST all over the universe where massive objects have once been.

So how far in the opposite direction from "deformed" does ST go? To continue the fabric analogy; does ST move more towards a loose mesh in the absence of matter? Or is there a pervasive steady state?

If ST does "loosen" the further away from mass it is, could this be a source of inflation?

Surely someone smarter than me must have wondered this.
Right, so... yes, spacetime curvature is how gravity acts. That is the rather beautiful concept underlying what Einstein did. However, the analogy of spacetime as some higher-dimensional rubber sheet is just a useful tool to communicate that to the public. You were talking about elasticity, and forces behind that, and even though those things do exist on a rubber sheet, none of that stuff is in the theory of general relativity.

There is a "non-deformed" state of spacetime - it's called Minkowski space, or flat space. Of course, it doesn't exist anywhere in the universe, since the universe has matter - even the places that don't have matter are affected by matter elsewhere - but any region of spacetime on small enough scales looks pretty similar to it, in the same way that even though the Earth is curved, on small scales the surface looks flat. Minkowski space is just like the flat surface, but in higher dimensions (and with some funny stuff to account for the time dimension).

Also (slightly unrelated?): this picture doesn't eliminate the need for a graviton particle. In fact, this came before we knew what a graviton was. In something called quantum field theory, forces become particles - for example, the electromagnetic force becomes a photon. The same things happen when you quantize gravity. These different pictures - forces, spacetime, particles - equally "right" ways of looking at the same thing. It just depends how you look at it.

R

#### ramparts

##### Guest
5hot6un":29fmnglf said:
Jerromy":29fmnglf said:
"Waves" implies a variance in a field. If there were some type of waves to the force of gravity I'm sure we'd have figured it out by now. Newton may not have had the insight but Einstien did and he determined that gravity is a field, not a "wave of gravitons".
Einstein's GT does not say gravity is a field. Newton suggested that. Einstein explained that gravity is the deformation of space-time.

That's kind of the point of this tread. Einstein's deformed ST implies it is a medium.

There is an active search for gravity waves.
http://www.spacedaily.com/news/gravity-05f.html

The term gravity waves is wrong in my opinion. They are space-time waves. Ripples in the ST medium.
Having read the rest of this thread, I would humbly suggest that you change your approach. You came into this thread asking questions because you don't know something about science, and then in the rest of your posts act as if you already know all of the science. It is quite clear that you don't; that's fine, there's nothing wrong with that, but you shouldn't be off asserting things like "Einstein's GT does not say gravity is a field" which are simply untrue. In GR, gravity is a field - it's a tensor field, to get all jargon-y. A tensor is just a type of mathematical object, and these particular tensors describe the curvature of spacetime at each point. It's a different field than the one used in Newtonian physics, but it's still written in the language of fields.

Also, a minor thing, it's hurting my head to read "ST" all the time No one uses that - just write "spacetime", it'll make your posts easier to read.

5

#### 5hot6un

##### Guest
ramparts":20il72sj said:
Having read the rest of this thread, I would humbly suggest that you change your approach. You came into this thread asking questions because you don't know something about science, and then in the rest of your posts act as if you already know all of the science. It is quite clear that you don't; that's fine, there's nothing wrong with that, but you shouldn't be off asserting things like "Einstein's GT does not say gravity is a field" which are simply untrue. In GR, gravity is a field - it's a tensor field, to get all jargon-y. A tensor is just a type of mathematical object, and these particular tensors describe the curvature of spacetime at each point. It's a different field than the one used in Newtonian physics, but it's still written in the language of fields.

Also, a minor thing, it's hurting my head to read "ST" all the time No one uses that - just write "spacetime", it'll make your posts easier to read.
I appreciate the feedback. I certainly do not mean to act as if I know all the science. But I do understand some of it.

I am here to get exactly what you just provided. A better understanding.

If my current understanding is wrong, I want to know. If espousing what I think I understand comes off as an act, I'm not sure what to do about it.

I stand behind my assertion that gravity is not a field, at least in the context of the post that I replied to. I am glad you set me straight where I was wrong.

5

#### 5hot6un

##### Guest
ramparts":3oi7c9mg said:
Right, so... yes, spacetime curvature is how gravity acts. That is the rather beautiful concept underlying what Einstein did. However, the analogy of spacetime as some higher-dimensional rubber sheet is just a useful tool to communicate that to the public. You were talking about elasticity, and forces behind that, and even though those things do exist on a rubber sheet, none of that stuff is in the theory of general relativity.

There is a "non-deformed" state of spacetime - it's called Minkowski space, or flat space. Of course, it doesn't exist anywhere in the universe, since the universe has matter - even the places that don't have matter are affected by matter elsewhere - but any region of spacetime on small enough scales looks pretty similar to it, in the same way that even though the Earth is curved, on small scales the surface looks flat. Minkowski space is just like the flat surface, but in higher dimensions (and with some funny stuff to account for the time dimension).

Also (slightly unrelated?): this picture doesn't eliminate the need for a graviton particle. In fact, this came before we knew what a graviton was. In something called quantum field theory, forces become particles - for example, the electromagnetic force becomes a photon. The same things happen when you quantize gravity. These different pictures - forces, spacetime, particles - equally "right" ways of looking at the same thing. It just depends how you look at it.
I have more questions. Please read them as if written in the tone of an inquisitive child.

By what mechanism does a section of spacetime return to a less deformed state when a massive object moves further away?
In my mind, this question conjurers up visions of spacetime acting as a physical thing.

I also wonder if the section of spacetime moves back to a less deformed state at the speed of light or at some other rate?

M

#### Mee_n_Mac

##### Guest
5hot6un":3npnbvk9 said:
I have more questions. Please read them as if written in the tone of an inquisitive child.

By what mechanism does a section of spacetime return to a less deformed state when a massive object moves further away?
In my mind, this question conjurers up visions of spacetime acting as a physical thing.

I also wonder if the section of spacetime moves back to a less deformed state at the speed of light or at some other rate?
I can answer the last one. Right now the last measurements had gravity propagating at the speed of light, give or take. Since gravity is the deformation of spacetime (or is it space-time ?) you can say changes in this deformation (gravity waves) move at the speed of light. I note that there was some dispute that Kopeikin's experiement actually measured the "speed of gravity". I don't know if that dispute was ever resolved.

C

#### centsworth_II

##### Guest
Mathematical models may describe observations very well, but they do not necessarily represent physical reality. I do not see how relativity theory's fine description of observations translates to a proof for or against the physical reality of gravitons.

R

#### ramparts

##### Guest
General relativity predicts that changes in the gravitational field propagate at the speed of light (in the particle picture, this corresponds to the prediction that gravitons are massless, like photons - which is why gravity and electromagnetism would propagate at the same speed). Experimental tests are pretty consistent with this.

As for your other question, about the "mechanism" at which spacetime deforms and undeforms, that's trickier. On the one hand, I'm not entirely sure how to answer it, or if there even is an answer that you would find satisfying. Spacetime is a manifold which acts in certain ways, and those ways are governed by a set of equations called the Einstein field equations (see my user pic). When it comes down to it, that's no worse a description than of any other physical process, but since according to GR there is no underlying mechanism, that's as far as we can go.

It is possible there is more to it; we're hoping that a fuller understanding of GR on the quantum level will help elucidate the precise nature of spacetime. There are still two fields of philosophical interpretation of GR - one which sees spacetime as an actual, physical manifold upon which all physics happens, and the other which sees it as just a useful mathematical construct to describe something entirely different.

I hope that made sense - I can imagine you might have some more questions, but the take-home message is this: to the best of our knowledge, there is no "mechanism", but that could conceivably change when we understand more

F

#### FlatEarth

##### Guest
ramparts":3bkphcun said:
It is possible there is more to it; we're hoping that a fuller understanding of GR on the quantum level will help elucidate the precise nature of spacetime. There are still two fields of philosophical interpretation of GR - one which sees spacetime as an actual, physical manifold upon which all physics happens, and the other which sees it as just a useful mathematical construct to describe something entirely different.
It seems to me that there is only one useful interpretation of GR- the one that sees spacetime as something real, not just a measure of distance and motion. For all his brilliance, Einstein had difficulty with some of the key precepts of quantum mechanics, but we know that the only way to explain the very large is to understand the very small. QED explains what spacetime is, and it cannot be ignored.

Status
Not open for further replies.