What is space?

  • Thread starter Philip7575
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  • #1
I'm brand-new to this site, an English teacher, certainly not a physicist, but I'd sure appreciate some (gentle) help.

The short version of my question:

How can the universe expand into infinite space?

Are there two kinds of space? The first is the distances between galaxies in our universe, and the second, space, is something else?

Where did space come from? Was it there before the Big Bang?

If there is space and space, why isn't there time and time?
 

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  • #2
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Hey Philip welcome to the Forum.

I have been full circle round this question here in this thread where I got lost on older Physics concepts such as the aether:

https://www.physicsforums.com/showthread.php?t=487911&highlight=properties+of+space


My conclusion is that space has no objective existence whatsoever in the same way that ponderable matter does. By itself it is just a measurement of the distance or the separation between two physical objects, similar to the separation between two points in time. It is also a framework in which ponderable matter can "hang". It is also a void through which force carriers can propagate, but it is the characteristics of the force carriers which determine the way in which they behave and interact with ponderable matter. I believe that this is the most modern view and it replaces the older concepts of space being an aether with properties of its own.
 
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  • #3
I'm reading The Hidden Reality by Brian Greene. Here's his explanation (buried in a note at the bottom of p. 138): "If space were infinitely big, you might wonder what it means to say that the universe is larger now than it was in the past. The answer is 'larger' refers to the distances between galaxies today compared with the distances between those same galaxies in the past . . . . In the case of an infinite universe, 'larger' does not refer to the overall size of space, since once infinite always infinite. But for the ease of language, I will continue to refer to the changing size of the universe, even in the case of infinite space, with the understanding that I'm referring to changing distances between galaxies."

While physicists and cosmologists are usually precise, I can't grasp these two uses of the word space. One kind of space means one thing, and another space means something else.

Furthermore, I understand (I think) that if all matter and energy were removed from the universe, then time and space would vanish, too. But why wouldn't space disappear? And since General Relativity is about spacetime, why isn't there spacetime?
 
  • #4
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The distance between distant galaxies is increasing and accelerating due to dark energy. The universe is to al intents and purposes infinite, whilst the observable universe is finite and getting smaller all the time, due to expansion making the most distant parts no longer observable. I am not sure what you are confused about?
 
  • #5
phinds
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The distance between distant galaxies is increasing and accelerating due to dark energy. The universe is to al intents and purposes infinite, whilst the observable universe is finite and getting smaller all the time, due to expansion making the most distant parts no longer observable. I am not sure what you are confused about?

"to all intents and purposes" begs the question of IS it infinite or not, and that is a heavy discussion, not to be dismissed lightly even though you ARE right that it is irrelevant to our direct experiences.
 
  • #6
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I'm brand-new to this site, an English teacher, certainly not a physicist, but I'd sure appreciate some (gentle) help.

The short version of my question:

How can the universe expand into infinite space?

Are there two kinds of space? The first is the distances between galaxies in our universe, and the second, space, is something else?

Where did space come from? Was it there before the Big Bang?

If there is space and space, why isn't there time and time?

I don't think I could add anything to Tanelorn's excellent comments on space, I just wanted to add a note about the Big Bang. It is a highly controversial subject as to what, if anything, came before the big bang. The currently accepted model of cosmology basically says that we know a lot about what happened AFTER the singularity and absolutely nothing about the singularity itself or any possible "before" ("before" doesn't really exist in the standard cosmological model).

So you're next question HAS to be "how can something come out of nothing?". I can only suggest that you stock up heavily on headache pills and read about Quantum Mechanics.
 
  • #7
The--or maybe I should say "our"--universe is infinite? I'm paraphrasing from the Brian Green book, but one of the things we know pretty certainly is that the expansion of the universe is speeding up. That's what Perlmutter et al just got a Nobel Prize for.

Researchers have been able to calculate the cosmological constant--the amount of dark energy in the universe necessary to account for this expansion--by the simple algebra of flipping E=mc2 around to M=e/c2. The data from the faster-than-expected expansion requires a cosmological constant of just under 10-29 grams in every cubic centimeter of space.

The number of cubic centimeters in our universe is big, but it is not infinite.
 
  • #8
phinds
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The number of cubic centimeters in our universe is big, but it is not infinite.

You should not make definitive statements on this forum that you cannot back up with science. What you have stated is an unsupportable personal opinion. You MAY be right, but you may be wrong, and either way, you can't prove it, so stating it as fact is not a good idea.
 
  • #9
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Hi Philip7575

I can only suggest that you stock up heavily on headache pills and read about Quantum Mechanics.

Another way of getting a really good headache is to Google “Cosmic Topology.”
 
  • #10
phinds:

Jeez, I'm an English teacher. How could I possibly have a personal opinion about the cosmological constant or the size of the universe in cubic centimeters?

I'm paraphrasing Brian Greene's The Hidden Reality, p. 138 and p. 337 n. 8 and 9. Greene is a professor of physics and mathematics at Columbia University, and a well-respected populizer of tough science like this. His first book, The Elegant Universe, was a finalist for the Pulitizer Prize. And I'm getting that information from the book's dust jacket, so it's not "unsupportable personal opinion," either.

The point is that if researchers can calculate the cosmological constant by plugging the total amount of dark energy in the universe into that calculation, the total amount of dark energy must be finite. Put another way (and this is me, not Greene), if the universe were infinite, then the total amount of dark energy in it would also have to be infinite. Put still another way (me again, not Greene), if the universe were infinite how could it be expanding?
 
  • #11
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The point is that if researchers can calculate the cosmological constant by plugging the total amount of dark energy in the universe into that calculation, the total amount of dark energy must be finite. Put another way (and this is me, not Greene), if the universe were infinite, then the total amount of dark energy in it would also have to be infinite.

Makes sense to me.

Put still another way (me again, not Greene), if the universe were infinite how could it be expanding?

Not necessarily. 2 times infinite is still infinite.
 
  • #12
Imax: "2 times infinite is still infinite."

To cite Greene again, "In the case of an infinite universe, 'larger' does not refer to the overall size of space, since once infinite always infinite."

This is one of the things that led to my initial question. If the universe is infinitely large, then it can't get any bigger. So physicists talk about space in our finite universe at the same time they say our finite universe is expanding into infinite space.

It's these two uses, space vs. space that I don't understand.
 
  • #13
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phinds:

Jeez, I'm an English teacher. How could I possibly have a personal opinion about the cosmological constant or the size of the universe in cubic centimeters?
QUOTE]

I would think an English teacher would understand that when you make a statement without quotes around it, folks will perceive you as being the author of the statement. You seem offended that I had that perception.
 
  • #14
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How can the universe expand into infinite space?

Are there two kinds of space?

Where did space come from?

Was it there before the Big Bang?

Welcome to the forum Philip, I too am new at this and sometimes catch myself making factual statements that really need to be prefaced with "My Opinion is"

First of all there is only one kind of space. The space between galaxies is the same as the space inside atoms. There may be differences like temperature, density, fields etc. but space is space.

I believe the universe works in cycles so yes there would have been space before the Big Bang. Space from the last cycle would have condensed down to a singularity, during which time there would not have been any space.

I think the universe is formed from an finite number of extremely small particles. These particles may be condensed into matter as we know it or diffused to the point we can't see them. As they move in relation to each other they each form electromagnetic fields. I believe it is the combination of these fast moving particle and their fields that make space as we know it.

As for your first question, the universe is not expanding into space. Space IS what expands.
 
  • #15
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This is one of the things that led to my initial question. If the universe is infinitely large, then it can't get any bigger. So physicists talk about space in our finite universe at the same time they say our finite universe is expanding into infinite space.

It's these two uses, space vs. space that I don't understand.

There’s only one space. The space in our universe isn’t expanding into some other outside space. If the universe is finite, then travelling a straight line in any direction can bring you back to where you started. It’s just like here on Earth. The big difference is that space has 3 dimensions, whereas here on Earth, gravity restricts up and earth down.

Brian Greene gave a good description of expansion:

In the case of an infinite universe, 'larger' does not refer to the overall size of space, since once infinite always infinite. But for the ease of language, I will continue to refer to the changing size of the universe, even in the case of infinite space, with the understanding that I'm referring to changing distances between galaxies.

Mathematically, a finite space can expand, remain static, or contract. Our Universe seems to be expanding.
 
  • #16
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Mathematically, a finite space can expand, remain static, or contract. Our Universe seems to be expanding.

I believe it expands and contracts but never static or the cycle would stop. And yes our universe does seem to be expanding but I wonder?
 
  • #17
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Hi Philip, from one boffin to another, I'll give it a go at explaining. Not that long ago, I had a similar confusion.. what is expanding into what.. and I also ran into the "universe is infinite" conundrum. It eventually made sense to me, even though I haven't seen any of the math (and probably would struggle with it if I did).

What is finite? Our observable universe (OU) is finite. It is a spherical distance beyond which we cannot see. There are two reasons for this. The first is that the light from stars beyond that have not yet reached us. The second is (and this will be difficult, but more on it later) that the universe is expanding, faster than light, meaning that some of the light from beyond our OU will never reach us.

What is infinite? The whole universe, not just our OU, is believed to be infinite, according to the more popular models. As background to this, people also get confused with the Big Bang, thinking of it like an explosion that happened in one place and spread beyond that centre. The name, Big Bang, was given to it by one of its early detractors. The actual model says that when the BB occurred, it happened everywhere (infinitely), in the same instant.

What is expansion? Expansion, as has been said in this thread, is the growing distance between galaxies, but more specifically, between matter that is not bound by gravity to other matter. Just as our Moon is tied in orbit to us, and us in orbit to the Sun, so are galaxies tied to other galaxies. Expansion is putting more distance between galaxies that are not so bound.

An important intermediate point is to be understood about light speed (c). It is believed that nothing can travel faster than light, even galaxies relative to each other. Yet in this expansion, the distance between some galaxies is growing at faster than light speed. Sounds like a contradiction? I'll explain.

The distance between such distant matter is growing in two ways. The first way is their actual movement, relative to each other, a concept we readily understand from everyday experiences. The second way that the distance is growing is that dark energy is impacting on space-time in a way that effectively puts more distance between the two objects. Still confused? So was I.

The best way that cosmologists have attempted to represent, what is essentially a mathematical model, is by using a 2-dimensional analog of 3 dimensional space, by asking us to imagine that the universe is like a balloon. Travel anywhere on that balloon's surface and you will find no end point. Objects on the surface of the balloon will move relative to each other. Add air to that balloon, and the distance between objects grows, in part from their own movement and in part from the expansion of that balloon. So, add the slower than light movement of the objects, relative to each other, to the expansion, and you can see how the growth in distance can exceed the light speed limit.

As I say, this is my boffin explanation, much of which I've learned from the patient ones here. Our Earth-bound paradigms make it difficult to comprehend some of these ideas, but as they've rolled around in my head, I could see the logic.

Does that help at all?

Oops.. I just looked up boffin.. the online dictionary uses words like "scientist" and "expert". :blushing: I'm not a scientist, nor an expert - just someone who asks, listens and learns about this fascinating subject.
 
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  • #18
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Narrator, that's a great explanation. Just to expand one point a little, it's VERY important to remember that the balloon analogy is JUST and analogy, and it's even more important to remember that you can only consider the surface of the balloon. People often look at the balloon analogy and start talking about the fact that it is a hollow shell with a center. In the analogy, you cannot consider the center; there IS no center, there is ONLY the surface.
 
  • #19
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I believe it expands and contracts but never static or the cycle would stop. And yes our universe does seem to be expanding but I wonder?

So you dispute the evidence that is believed by essentially all physicists? You might want to read up on the evidence a bit before you make such a cavalier statement.
 
  • #20
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I believe it expands and contracts but never static or the cycle would stop. And yes our universe does seem to be expanding but I wonder?

With the observation of the acceleration in the expansion of the universe, I don't see how it could slow down and contract, since this observation shows the exact opposite.
 
  • #21
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With the observation of the acceleration in the expansion of the universe, I don't see how it could slow down and contract, since this observation shows the exact opposite.
As I understand it, it's still theoretically possible, though not so favoured a model, now that we know the expansion seems to be accelerating.
 
  • #22
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"The final frontier"
 
  • #23
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So you dispute the evidence that is believed by essentially all physicists? You might want to read up on the evidence a bit before you make such a cavalier statement.

I'm not the first to wonder and hopefuly not the last.
 
  • #24
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With the observation of the acceleration in the expansion of the universe, I don't see how it could slow down and contract, since this observation shows the exact opposite.


There was a time when no one could imagine the universe unless earth was at the center. There’s always other ways to interpret data.
 
  • #25
Some of these comments are getting off-track, but that's the nature of any blog.

To summarize (at least what's in my head):

Our universe is finite but expanding. The space in our universe, for example, the distance between galaxies, is also finite but expanding.

Our universe is expanding into something called infinite space.

And that's the ambiguity/imprecision: Space is used two different ways. No doubt, this is because of the limitations of language: There are many examples of phenomona, especially in quantum mechanics, that are impossible to visualize or grasp. This is another example.

Fair enough?
 
  • #26
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My conclusion is that space has no objective existence whatsoever in the same way that ponderable matter does. By itself it is just a measurement of the distance or the separation between two physical objects, similar to the separation between two points in time. It is also a framework in which ponderable matter can "hang". It is also a void through which force carriers can propagate, but it is the characteristics of the force carriers which determine the way in which they behave and interact with ponderable matter. I believe that this is the most modern view and it replaces the older concepts of space being an aether with properties of its own.

I am only a layman but my impression is that relativity says space can curve. And this has been verified by the fact that light from a distant star passing near a closer star will curve toward the closer star more than would be case in a "flat" space such as a Euclidian space as conceived by Newton. This is because the gravity of the intervening star is causing space to curve and light to follow its curved path. Space is therefore flexible and other than a simple void or a mere framework to hang things on. Also relativity says space is intimately linked with time in an entity properly called spacetime. Movement of an object through space quickly will slow that object's time down as compared with the passage of time on an object moving slower. This has also been verified by experiment with very accurate atomic clocks. Therefore it is difficult to speak of space at all without speaking also about time.
 
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  • #27
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chaszz, yes I agree that the presence of large amounts of Matter (fermions) will interact with and bend light (photons). I think therefore that space appears curved to an observer, although there is no ponderable thing actually present in space which is being warped.

Also with the relativity experiment, I do not believe that anything present in space or space time is causing the effect, it is all a result of the effects of acceleration on the Fermions (matter) and Bosons (force carriers). I am saying all this in a rhetorical tone, I am just a old forgetful balding Engineer trying to rediscover Physics and learn about the latest theories of Cosmology :)
 
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  • #28
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Some of these comments are getting off-track, but that's the nature of any blog.

To summarize (at least what's in my head):

Our universe is finite but expanding. The space in our universe, for example, the distance between galaxies, is also finite but expanding.

Not quite...the "observable universe" - the tiny chunk of the universe that we can see - is finite. It's limited by how far light could have travelled in the amount of time that the universe has existed, with some extra complications thrown in by expansion. Basically, we can't see anything outside the observable universe because there hasn't been enough time for light from there to reach us. So the amount of the universe we can see is finite.

As for the actual whole of the universe? In a sentence, we don't know if it's finite or infinite. This has to do with the curvature of spacetime, and the current data isn't precise enough to pin down which it is. So we don't know right now, and people work with both models - sometimes right alongside each other. Better data in the future might give us a clear answer.

But yes - either way, finite or not, it is expanding.

And yes - the distance between any given galaxies is finite but expanding.

Our universe is expanding into something called infinite space.

And that's the ambiguity/imprecision: Space is used two different ways. No doubt, this is because of the limitations of language: There are many examples of phenomona, especially in quantum mechanics, that are impossible to visualize or grasp. This is another example.

Fair enough?

(Disclaimer: I am simply here transmitting conclusions which I understand to be true (from the FAQ, for example, which might help you), but have no knowledge of how to derive them)

No, there is no space outside the universe. The universe is not like a sphere, expanding at lightspeed into a bigger emptiness 'outside' of it. There is no 'outside' to the universe in the spacial sense. The universe, if it is infinite, has no edges. If it is finite, it also has no edges. This is similar to how the finite, 2d surface of the earth has no edges. Except in 3d, which is not as easy to visualize.


This much answers (I hope!) your questions. The wall of text below is more for fun.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(Disclaimer: now I am sharing an illustration I like to use, which is not based on data and is not accurate, but merely gives a sense of how a finite 3d space can have no boundaries/edges)

The way I like to visualize it is to imagine the universe as a cube filled with the stuff of the universe (superclusters of galaxies, filaments and voids, etc). You are in a transwarp spaceship inside of the cube (because you are in the universe). Pretend your spaceship goes as fast as you want, provided you clench your teeth and think really hard. ;)

So what happens if you fly out of the cube? Well, you don't, you simply come back in the other side. If you fly out the top side, you've just come up through the bottom side. If you fly out the east side, you've only just come in through the west, etc. So you can fly as far as you like any which way and you stay inside the universe.

Now, here's the cool part: you're not the only thing going out one side and coming in the other. The light (and gravity) radiated by all the stars, galaxies and whatnot also crosses sides in a similar way. So when you are approaching the east side of the cube, you are encountering the light that has just crossed the other way, going out the west side and coming in east. So you see ahead of you all the galaxies that are near the west side of the cube, even though you haven't left the east side yet. And when you actually cross out of the east side and come into the west, you are encoutering that same light. So when you "cross" from east to west, nothing changes visually. There is no jump or flicker in the image on your main screen. There wouldn't be any changes or brief interruptions in your ship's (or your body's) functioning. The transition would, if fact, be completely undetectable.

Crossing the "edges" of the universe is completely indistinguishable from not crossing them. Because of this, there is no way for you in your ship to map the "edges" of the universe, or find its center. In fact, you could pick any random point in the universe and arbitrarily define it to be the center, and figure out accordingly where the edges are, and it would work; you would have a functioning map. This is of course because, in fact, there are no edges - they are simply a useful device for us to visualize what we otherwise can't understand - that space just "wraps back in on itself". Mysteriously, as far as I'm concerned. ;) But there's math for people who want to get it.

Differences between this illustration and reality

I stress again that the above is only an illustration, and reality (even if we did have a spaceship that could fly as fast as we want) would behave differently. Here are some of the ways they differ...

1. In the illustration, space is geometrically what one would call a "3-torus", the 3d counterpart of the surface of a 2-torus, or doughnut shape. In reality, space is geometrically a 3-sphere, the 3d counterpart of the surface of a 2-sphere, or (basket-, soccer, tennis) ball shape. All the other differences listed are based on this difference. [PF veterans: if I screwed up any terminology here, please correct me!]

2. In the illustration, there are only six directions you can go that would bring you exactly back to where you started after "crossing the universe" once. That is, only if you go straight up, straight down, or straight north, south, east, or west. Visualize the cube: if you leave the center (works for any point, but take the center) going perfectly perpendicular to one set of faces of the cube, you will arrive exactly back at that point. If you leave the center going at a very slight angle instead, then you don't quite arrive back at the center after one lap. Depending on your angle, it could take an arbitrarily large number of laps to get back to the center. Not so with reality. Any direction you take will bring you back to your starting point with the same distance travelled.
To see the 2d analog of this, imagine a point on a doughnut's surface, say on the outer circumference. Only if you travel exactly around the outer circumference of the doughnut or exactly perpendicular to it will you end up back at your starting place. Travel any other angle, and you go crisscrossing all over the doughnut for who knows how long until you get back. Take a sphere, now, and select a point on its surface. From this point, you can travel any direction, and after 1 circumference-worth of travel, you end up back where you started.

3. (Directly following from 2.) In the illustration universe, there is actually something you could map by flying around, and that is the axes of the universe. A 3-torus universe would have 3 axes, which you could identify by finding out which directions, when flown, immediately bring you back to your starting point. In reality, there are no such axes, specifically because there is no difference in flying different directions.

[PF veterans: if you notice any other differences I missed, I'm curious to know what they are! Please do post them - thanks!]
 
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  • #29
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chaszz, yes I agree that the presence of large amounts of Matter (fermions) will interact with and bend light (photons). I think therefore that space appears curved to an observer, although there is no ponderable thing actually present in space which is being warped.

Also with the relativity experiment, I do not believe that anything present in space or space time is causing the effect, it is all a result of the effects of acceleration on the Fermions (matter) and Bosons (force carriers). I am saying all this in a rhetorical tone, I am just a old forgetful balding Engineer trying to rediscover Physics and learn about the latest theories of Cosmology :)

Tanelorn, your interpretation of the facts is contrary to relativity, which is the currently accepted theory of space, time, acceleration and gravity. What you say in your first paragraph would lead to a Newtonian displacement of the light, which is considerably less than the Einsteinian (relativistic) displacement. General relativity predicted this and Eddington's landmark 1919 experiment confirmed the prediction to a high degree of accuracy.

The airplane experiment is another test which has supported relativity. This experiment uses constant speed in the airplane, not accelerated (increasing) speed, so your reference to acceleration is inaccurate.

Your theory using the fermions and bosons is interesting, but with all due respect I think you should remember that both the special and general theories of relativity have made predictions which have been borne out many, many times by experiments over the last hundred years or so. Many scientists have tried to prove these theories wrong but have not succeeded in doing so. This is whole orders of magnitude different from a private opinion unsupported by experimental proof.
 
  • #30
Welcome philip Im also new to the forum and i'm so glad I found it. People here are nice and well informed and they know what they are talking about.
 
  • #31
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Also with the relativity experiment, I do not believe that anything present in space or space time is causing the effect, it is all a result of the effects of acceleration on the Fermions (matter) and Bosons (force carriers).

What acceleration the fermions and bosons?
 
  • #32
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Bill and Chaszz, yes this is how I am interpreting what I have recently read. I could be mistaken in my interpretation, but when you remove all physical qualities and properties from the aether of space itself, all that is left is the characterisitics, properties, and interactions of the fermions and bosons themselves. Fermions and Bosons therefore ultimately have to be responsible for all observed phenonema. As I said before though, I need a professional Physicst to confirm this.
 
  • #33
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Bill and Chaszz, yes this is how I am interpreting what I have recently read. I could be mistaken in my interpretation, but when you remove all physical qualities and properties from the aether of space itself, all that is left is the characterisitics, properties, and interactions of the fermions and bosons themselves. Fermions and Bosons therefore ultimately have to be responsible for all observed phenonema. As I said before though, I need a professional Physicst to confirm this.

My question was suppose to be

What accelerates the fermions and bosons?
 
  • #34
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A rocket ship is one possibility. You get angular acceleration just orbiting Earth.
 
  • #35
Space is simply area. A location for matter and energy to be and travel. Air is different, it contains stuff - usually undetectably (not a word - i know) small for us to see. Please don't be rude if this doesn't help.
 

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