What is Space? A Theory Exploration

[Nereid]

(A belated) Welcome to Physics Forums metech00!

So there seem to be various philosophical ideas on what 'space' is, and others which explicitly acknowledge their theoretical ancestry (along the lines of "whatever GR says 'space' is, that's what it is!"), and Chronos' delightful operational definition!

Looking at it from another point of view, how does thinking about 'space' help build better physics? For example, can such thinking lead to new tests/experiments? interesting extensions of highly successful theories (specifically GR or QFT)? Or are most such deep musings and ponderings merely jolly good fun mental gymnastics?

Historically, how direct a role did 'space' play in helping Newton, Einstein, Maxwell, the 1920s quantum trail blazers, today's LQG and String/M-Theoreticians come up with - or tame into equations - their revolutionary new ideas?

 

[sd01g]

(A belated) Welcome to Physics Forums metech00!

oSo there seem to be various philosophical ideas on what 'space' is, and others which explicitly acknowledge their theoretical ancestry (along the lines f "whatever GR says 'space' is, that's what it is!"), and Chronos' delightful operational definition!

Looking at it from another point of view, how does thinking about 'space' help build better physics? For example, can such thinking lead to new tests/experiments? interesting extensions of highly successful theories (specifically GR or QFT)? Or are most such deep musings and ponderings merely jolly good fun mental gymnastics?

Historically, how direct a role did 'space' play in helping Newton, Einstein, Maxwell, the 1920s quantum trail blazers, today's LQG and String/M-Theoreticians come up with - or tame into equations - their revolutionary new ideas?

The goal is to try to understand gravity. GR is a hinderance. The concept of spacetime which is nothing more than a concept is preventing us from a proper understanding of the graviton. Warping spacetime, without telling how it does it, is useless. Trying to detect graviton waves from black holes is money poorly spent.

A proper understanding of spaces and time would prevent us from trying to combine them to produce a 'fabric' which no one has a clue what it is. Combining two concepts does not produce something REAL--only a more complex concept.

Anyway, this is how I see it. I hope I do not upset the administators.

 

[Nereid]

The goal is to try to understand gravity.

Is it reasonable then to ask "What do mean when you say 'gravity'?"

GR is a hinderance. The concept of spacetime which is nothing more than a concept is preventing us from a proper understanding of the graviton.

You've lost me; what is this "graviton"? Can I buy a dozen of them from my local Tesco supermarket?

Warping spacetime, without telling how it does it, is useless. Trying to detect graviton waves from black holes is money poorly spent.

Pretend I'm from Missouri (the 'show me' state); what sort of existence does 'spacetime' have, outside GR? other than in GR, what existence do 'black holes' have? If I read the material on the LIGO website, I learn that they (consumers of lots of money) are searching for gravitational radiation (not 'gravitons') - who is spending money 'trying to detect graviton waves'?

A proper understanding of spaces and time would prevent us from trying to combine them to produce a 'fabric' which no one has a clue what it is.

So if no one has 'a clue' as to what 'it is', how can we even discuss it, let alone devise experiments to measure it?

Combining two concepts does not produce something REAL--only a more complex concept.

Hmm, from reading Lewis Carroll, I see there is the concept of 'toves'; from reading Lear, I see the concepts of 'bong-tree' and 'runcible' - before I try to 'combine' them, to make something 'REAL', in what sense are 'toves', 'bong-trees', and 'runcible' 'REAL' to begin with?

Anyway, this is how I see it. I hope I do not upset the administators.

Since I'm only a 'Super Mentor', whether I'm upset or not is irrelevant, right?

 

[metech00]

(A belated) Welcome to Physics Forums metech00!

So there seem to be various philosophical ideas on what 'space' is, and others which explicitly acknowledge their theoretical ancestry (along the lines of "whatever GR says 'space' is, that's what it is!"), and Chronos' delightful operational definition!

Looking at it from another point of view, how does thinking about 'space' help build better physics? For example, can such thinking lead to new tests/experiments? interesting extensions of highly successful theories (specifically GR or QFT)? Or are most such deep musings and ponderings merely jolly good fun mental gymnastics?

Historically, how direct a role did 'space' play in helping Newton, Einstein, Maxwell, the 1920s quantum trail blazers, today's LQG and String/M-Theoreticians come up with - or tame into equations - their revolutionary new ideas?

Nereid, thanks for the greeting. Personally, I'm quite attracted to the M-Theory perspective on things, espectially the ADDK model that helps define dark matter via folded branes. I feel comfotable with branes and the BULK in general. The description of the big band (or big bump) seems eloquent to me.

Still, the concept of space simply appearing all around us makes me wonder where its coming from. I was hoping someone might point me to some current work that addresses the physical aspects of space itself. That would be helpful.

 

[pervect]

The goal is to try to understand gravity. GR is a hinderance. The concept of spacetime which is nothing more than a concept is preventing us from a proper understanding of the graviton. Warping spacetime, without telling how it does it, is useless. Trying to detect graviton waves from black holes is money poorly spent.

A proper understanding of spaces and time would prevent us from trying to combine them to produce a 'fabric' which no one has a clue what it is. Combining two concepts does not produce something REAL--only a more complex concept.

Anyway, this is how I see it. I hope I do not upset the administators.

GR is far from useless. It makes testable predictions - predictions that have so far held up to all tests to date. GR is not at all vague about how spacetime is warped, it is expressed in the elegant equation

G_uv = 8*Pi*T_uv

The left side of the equation describes exactly how space is warped - the right side of the equation is dependent on the distribution of matter and energy.

Since space and time "mix together" via the Lorentz transform, they are not isolated and independent concepts to be studied separately. One observer's space is another observers time.

It would really be a good idea to get a good idea of what a theory actually says before attempting to criticize it.

 

[sd01g]

GR is useful because it helps explain movement and position of matter/energy. It is useless when it comes to explaining how and why spacetime is warped and it does not even give a good definition of what spacetime actually is in terms of something REAL.

The original point of all this was to justify the effort of trying to understand what is 'time' and 'space' and what do you really get when the two are combined. All you really get in GR is a method of observing that takes into consideration that everything in the universe is moving including the observer. Somehow, this gets converted into a 'fabric' of some sort and is used to explain how gravity works.

The quantum concept of a gravity particle called the graviton seems to me a better approach to explaining the force of gravity. We should be attempting to design experiments to detect and generate this particle.

 

[sscreenwritr]

Hello,
I'm quite sure I'm out of my league here, but I have a question.
The other night on the science channel there was a program about the expansion of the visible universe. By finding and determining the speed of supernovae, a physicist concluded that the universe is speeding up in its expansion. The supernovae furthest out were increasing their speed.
No logical mathematical explanation could be offered for this increase, which is to say,
no massive amount of matter exists beyond these supernovae generating an attraction by which to explain the increase in speed.
Logically, these stars should be slowing down.
Now we come to my question...Isn't this a linear way of looking at space?
Isn't it possible that as Einstein described the universe, a kind of tesselation, that we're seeing a fold back in toward the center of space and the supernovae are increasing in speed because they are being acted upon by the massive amount of mass which appears to be behind them, but is actually now in front of them?
Don't laugh.
I'm serious.
It just seems to me to be such a logical answer.
If you think about a circular roadway in which the cars are speeding around a loop, then there is a point at which the cars are actually speeding toward their original starting point.
Isn't that possible with the fabric of space?
Isn't it possible that we're seeing the place beyond the curve where the supernovae have made the turn and are now speeding back toward their point of origin?

Thanks for considering my question.
My email is sscreenwritr@rock.com

 

[lucid385]

For something to exist, there must be something for that thing to exist in. It is inconceivable to imagine anything not existing in something, whether that something is space or whatever. Now, I would like to tell you what I believe space to be, but first, I till ask the question: can you see lines and see squares? The answer to this question is frankly, no. One can never see lines nor squares because both are things which are not three dimenisonal--and human perception is limited to seeing the third dimension. A sheet of paper for example, is not a square, but rather, it is a flatened cube. The outline of my hand when seen over a background, is not a line, but only one part of my three dimensional hand. So, now, the next question is: what do all of the dimensions have in common? One answer is that all of the smaller dimensions, like the first and second for example, both are contained in the higher dimensions, like the third, and make up the higher dimensions. For instance, a line is contained in a plane, and a plane is contained in a three dimensional figure, and a three dimensional figure is contained in space. And furthermore, the first dimension creates the second, the second creates the thirds, and the third creates the fourth, and so on. Now, I have just shown that the third dimension both creates and is contained in the fourth. So, in other words, space is a higher dimension which is the very thing which containes ours, and the reason why we cannot see it is because we being human, ony have the power to see the third dimension. But, if we can only see the third dimension, how do we know of the first and second? Well, since these two dimensions are what build the third, and we completely understand the third, all we need to do is to break down the third dimension into its component part, namely the first and second dimension, and at that moment, we have the first and second dimension in our understanding. So, to recap, space is a higher dimension in which we exist, and the reason why we cannot see it is the fact that it is a higher dimension--we exist in space as fish exist in water.

 

[Nereid]

GR is useful because it helps explain movement and position of matter/energy. It is useless when it comes to explaining how and why spacetime is warped and it does not even give a good definition of what spacetime actually is in terms of something REAL.

What are some examples of REAL 'somethings'?

The original point of all this was to justify the effort of trying to understand what is 'time' and 'space' and what do you really get when the two are combined. All you really get in GR is a method of observing that takes into consideration that everything in the universe is moving including the observer. Somehow, this gets converted into a 'fabric' of some sort and is used to explain how gravity works.

Look at it from another POV:
- the theory gives you lots of pointers on where to look to test it (and so far GR's passed them all, with flying colours)
- the theory is fecund, in the sense that it gets you thinking about all kinds of other things, which you can go work out on
- there's no alternative (in terms of consistency with a similar breadth of observational and experimental results)
- ...

And how many other theories can you say this about?

The quantum concept of a gravity particle called the graviton seems to me a better approach to explaining the force of gravity. We should be attempting to design experiments to detect and generate this particle.

OK, I'll bite - how? Would you care to outline - at a million metres - what such an experiment might involve?

 

[Nereid]

Welcome to Physics Forums, sscreenwritr!

I think the quick answer to your question - it's certainly an interesting one - is that there would be all kinds of other effects that you should see if this kind of 'fold-back' were out there. For example, the CMBR angular spectrum would likely be very different from that which we actually observe.

 

[wisp]

If had space made of something then it should have been of smallest particles because otherwise nothing could have moved through it so easily. BUT if so then what is inbetween those particles ? So what do U think, Or Can U ?

Good thinking. The smallest particles would be ether particles, which have mass and bond together very strongly.
Anything that is different from ether would experience pressure forces as it moved through it, which could slow it down. So if matter is not different from the ether, it must be constructed of the ether in some way. The only solution is for matter to be caused by a hole in the ether. Around the hole the ether density reduces, forming a fundamental particle.

So space is full of tiny ether particles, and matter results because of their absence. Space has denser ether between particles of matter, and rarer ether around the holes or nothingness at the centres of particles.

But science will not accept the ether because its detection hasn't been officially verified, and because Einstein's space-time concept is more fashionable.

 

[ShadowKnight]

For something to exist, there must be something for that thing to exist in. It is inconceivable to imagine anything not existing in something, whether that something is space or whatever. Now, I would like to tell you what I believe space to be, but first, I till ask the question: can you see lines and see squares? The answer to this question is frankly, no. One can never see lines nor squares because both are things which are not three dimenisonal--and human perception is limited to seeing the third dimension. A sheet of paper for example, is not a square, but rather, it is a flatened cube. The outline of my hand when seen over a background, is not a line, but only one part of my three dimensional hand. So, now, the next question is: what do all of the dimensions have in common? One answer is that all of the smaller dimensions, like the first and second for example, both are contained in the higher dimensions, like the third, and make up the higher dimensions. For instance, a line is contained in a plane, and a plane is contained in a three dimensional figure, and a three dimensional figure is contained in space. And furthermore, the first dimension creates the second, the second creates the thirds, and the third creates the fourth, and so on. Now, I have just shown that the third dimension both creates and is contained in the fourth. So, in other words, space is a higher dimension which is the very thing which containes ours, and the reason why we cannot see it is because we being human, ony have the power to see the third dimension. But, if we can only see the third dimension, how do we know of the first and second? Well, since these two dimensions are what build the third, and we completely understand the third, all we need to do is to break down the third dimension into its component part, namely the first and second dimension, and at that moment, we have the first and second dimension in our understanding. So, to recap, space is a higher dimension in which we exist, and the reason why we cannot see it is the fact that it is a higher dimension--we exist in space as fish exist in water.

I think a better explanation along this line is that space itself belongs in 3 spatial dimensions but our entire 3d universe is itself contained in a 4 spatial dimension... something. Saying that space itself is the 4th spatial dimension is in my opinion quite a stretch, especially since we know we can travel through it and "see" it. I'm far from a physics major, but I recently used this analogy to convey my point:

"I've always believed that space, matter AND time all came into being with the big bang. The Big Bang was not an explosion IN space as many percieve, but an expansion OF space(time). Therefore prior to the big bang there was a void, but a void that lies outside the laws of our 3d universe. In other words (again my theorizing) the Big Bang was the expansion of our 3 dimensional universe inside of 4 dimensional space. Being 3 dimensional beings we can never fathom that 4 dimensional... universe? Can't think of a better word but this gets the point across. Now if this is true, we can think of the source of the Big Bang, that singularity, as being the creation point of 3d space in 4d. The best I can do to make an analogy of this is not very good. Imagine if you will, standing in a kitchen in our 3d universe, you poor a liquid into a large, flat cookie sheet. Let's say this liquid is a type of energy, the building blocks of matter for a 2 dimensional universe. As you poor this liquid into the cookie sheet you are essentially creating this 2d universe. The inhabitants of this 2d universe cannot possibly fathom a 3 dimensional space, so they cannot understand WHERE the sudden energy that created their expanding universe came from. They would have the same questions as us, we know there was an expansion (Big Bang) but WHERE did the energy that created it come from? These 2 dimensional inhabitants would theorize that there was a void, and somehow all the matter in their universe just appeared. What they can't possibly know is that this 'void' is really your kitchen in 3d space."

 

[lucid385]

I think a better explanation along this line is that space itself belongs in 3 spatial dimensions but our entire 3d universe is itself contained in a 4 spatial dimension... something. Saying that space itself is the 4th spatial dimension is in my opinion quite a stretch, especially since we know we can travel through it and "see" it. I'm far from a physics major, but I recently used this analogy to convey my point:

"I've always believed that space, matter AND time all came into being with the big bang. The Big Bang was not an explosion IN space as many percieve, but an expansion OF space(time). Therefore prior to the big bang there was a void, but a void that lies outside the laws of our 3d universe. In other words (again my theorizing) the Big Bang was the expansion of our 3 dimensional universe inside of 4 dimensional space. Being 3 dimensional beings we can never fathom that 4 dimensional... universe? Can't think of a better word but this gets the point across. Now if this is true, we can think of the source of the Big Bang, that singularity, as being the creation point of 3d space in 4d. The best I can do to make an analogy of this is not very good. Imagine if you will, standing in a kitchen in our 3d universe, you poor a liquid into a large, flat cookie sheet. Let's say this liquid is a type of energy, the building blocks of matter for a 2 dimensional universe. As you poor this liquid into the cookie sheet you are essentially creating this 2d universe. The inhabitants of this 2d universe cannot possibly fathom a 3 dimensional space, so they cannot understand WHERE the sudden energy that created their expanding universe came from. They would have the same questions as us, we know there was an expansion (Big Bang) but WHERE did the energy that created it come from? These 2 dimensional inhabitants would theorize that there was a void, and somehow all the matter in their universe just appeared. What they can't possibly know is that this 'void' is really your kitchen in 3d space."

Shadow Knight,
You did understand what I said about our dimension (3-D) as being contained in the higher fourth dimension. You also replied and said that space itself is three dimensional. Well, this assumption leads to a paradox--I will now explain: if space is indeed something and is three dimensional, then, why cannot we see it? Surely if space is both something and three dimensional, we should be able to see it. Even atoms are seen by us. The computer you are using to read this post is composed of atoms, so, when you look at your computer, you are looking at atoms. Now, have you ever seen space? Please, show me this three dimensional (as you are claiming) "thing"! It is impossible for you, or anybody for that matter, to do so. Why is this? This line of argument forces me to state that space is a higher dimension and that we human project out onto it a three dimensional nature. And furthermore, space, if it is a higher dimension, must have three dimensional properties, since, all lower dimensions create the higher ones. So, this is probably why we can successfully attribute a three dimensional character to space.
Now, I will explain why this higher dimension (if I am correct), this space, is so close to us, and why it contains our universe (in the last post, I spoke somewhat on these line, however, I will do so more here. Also, isn't one urged to think that space is a higher dimension, since, all higher dimensions contain the lower ones, and that fact that we KNOW that space contains everything in this universe (with the possible exception of time, but of all we know, time could even be space)?
Imagine a pyramid with one base and four sides. This object is a three dimensional one, which is built out of an infinite number of planes (infinite because the inside of the pyramid contains an infinite number of planes--one can always place a plane in between two adjacent planes--unless the plank length is true, but this is a topic for another time). Now, imagine that our universe is but one of these planes, which is contained in the greater pyramid. "our" two dimensional universe is so close to the three dimensional one, in which we are contained. The directions of up and down would to a being from the two dimensional universe be nothing. Hence, these directions would be seen as not existing. Likewise, we, who are three dimensional beings, do not see the fourth dimension, and according to what I have stated, we should be contained in the fourth dimension, and it should appear to us as none existent--and thus we are talking about and describing space

 

[HannonRJ]

Contrary to "modern" physics, Space is just void. It has no physical properties other than that it exists. It is "the stage" in which energy and time interact to produce our universe.

 

[ShadowKnight]

...Well, this assumption leads to a paradox--I will now explain: if space is indeed something and is three dimensional, then, why cannot we see it? Surely if space is both something and three dimensional, we should be able to see it.

My mind is open to all ideas until scientifically proven wrong. However have you considered the possibility that we cannot "see" space because it really IS nothing? Someone posted here earlier that space and time are there to prevent the same objects from being at the same place at the same time. In other words something is needed to separate objects, otherwise everything would be like the bing bang singularity, everything together in one "place" at one "time".

Or...

That space really is made of something (let's use the well worn fabric analogy) but that the constituents of this fabric are so small that we cannot "see" them. That one day we may may make a collider so large and powerful that it could show us this?

Or...

Good old string theory that takes your idea a little further and (to my understanding) proposes that space is actually made of of tiny rolled up dimensions, Calabi-Yau manifolds, again too small for us to "see".

I cannot come up with any good scientific reasons that space itself cannot be 4 spatial dimensions as you propose, maybe someone a little better versed in this can offer some reasons.

 

[Chronos]

To speak of 3D space being embedded in higher order dimensions without demonstrating a mathematical need for them to exist is metaphysics.

 

[lucid385]

My mind is open to all ideas until scientifically proven wrong. However have you considered the possibility that we cannot "see" space because it really IS nothing? Someone posted here earlier that space and time are there to prevent the same objects from being at the same place at the same time. In other words something is needed to separate objects, otherwise everything would be like the bing bang singularity, everything together in one "place" at one "time".

Or...

That space really is made of something (let's use the well worn fabric analogy) but that the constituents of this fabric are so small that we cannot "see" them. That one day we may may make a collider so large and powerful that it could show us this?

Or...

Good old string theory that takes your idea a little further and (to my understanding) proposes that space is actually made of of tiny rolled up dimensions, Calabi-Yau manifolds, again too small for us to "see".

I cannot come up with any good scientific reasons that space itself cannot be 4 spatial dimensions as you propose, maybe someone a little better versed in this can offer some reasons.

I myself am open to new ideas. It is this very fact which has lead me to this point in my inquiry of the universe.
To comment on what you said about there being a need for space to separate things, I will say two things. One, even in the singularity of the big bang there was some space, however small in volume, but nevertheless there. It is impossible to conceive of something, without that something having existence in something else--try it. Try to picture anything and see what happens. you will realize that you will never be able to imagine anyone thing without that thing existing in something else. And that something else will always ultimately be space. (If you imagine yourself at home, you have already "pictured" space, for this space is a requirement to the visualization of the image of you at home--and so is time.)
And two, as I have just stated, both space and time are prerequisites of human beings before we can conceive of anything, that is to say, for anything whatsoever to able to be understood, visualized, grasped, etc., the concepts of space and time must already be present in the mind--again, try it. Please try to imagine anyone thought without space and time being in that thought. If you can do this I would truly call you beyond human. And furthermore, all this about space and time being requirements of understanding, is the philosophy of Immanuel Kant.
And now, the concept of nothing doesn't make any sense (and might I add, even zero is something; even if it is something insomuch that it is nothing, it is still something.) To say that nothing EXISTS (as you proposed), is to make a positive assertion, whereby, one is stating that there indeed is something which exists. And hence, nothing cannot exist, for to say that nothing does exist, one is stating that there is SOMETHING which exists. But however, if we state that nothing does not exist, then space cannot be this nothing, for space does exist--we live in it.

 

[lucid385]

To speak of 3D space being embedded in higher order dimensions without demonstrating a mathematical need for them to exist is metaphysics.

And? What's wrong with metaphysics? If you like, regard metaphysics as step pne of the scientific method--hypothesis. And furthermore, Kant's idea of island universes (other galaxies) was in his time considered sepeculative nonsense. But today, we in fact know of the existence of other gallaxies. And moreover, somethings can exist only metphyically, and metaphysics is the only path to these things. The potentiallity of love is such a metaphysical thing. Reply if you wish me to explain why the potentials of things exist metaphysically.

 

[Nereid]

Chronos can speak for himself, of course, but I think he's spot on ... metaphysics may be interesting, it may be rewarding, etc, etc, etc, but it isn't physics (so waxing metaphysical would be OT for this thread - if you feel a metaphysical discussion of 'space' would be nice, please go ahead and start a thread in the Philosophy part of PF ).

 

[Chronos]

Affirming what Nereid said, metaphysics is not science. You must show the math to make your point. My response will be the Einstein equations. The stress-energy tensor is very compelling to me.