Galaxies moving away from eachother?

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ramparts

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FlatEarth":2gdpvax7 said:
origin":2gdpvax7 said:
This is your conjecture and is at odds with the scientific community. Your conjecture is not supported by current theory or observation.
Yes, it is conjecture on my part, but you make an incorrect statement when you say it is not supported by observation. What I've done is to try to explain logically what is observed without resorting to an unknown and likely non-existent force.
No, instead you resort to unknown and likely non-existent physics :lol:

FlatEarth":2gdpvax7 said:
1. Expansion of space-time was initiated at the BB and continues unabated.
Sure, that's what a Big Bang is - the beginning of expansion. No problem there.

2. Expansion of space-time accelerates and has always accelerated.
This is certainly controversial - given what we know of the matter and radiation contents of the universe, in the past both of those should have dominated the universe's energy content (radiation for the first few hundred thousand years, then matter for the next few billion years). Because these things exert an attractive gravitational pull, both of those eras - the radiation-dominated era and matter-dominated era - almost certainly exhibited a decelerating expansion. In the next few years we'll be able to probe back and see what the expansion actually looked like during the matter-dominated era, but we're pretty sure that's what we'll see.

So you've made a claim just by stating it, without giving any backing or evidence, while science makes the opposite by using well-established physics to make a prediction from solid data. You may be right, but it's much, much more likely science is ;)

3. The expansion of space-time is not driven by a force, but is analogous to gravity which is a distortion of space-time and not a force.
Well, if you're defining force that way, then there's no theory of dark energy which I know of which can be called a force. Various ideas include: a vacuum energy, whose gravitational effects would be repulsive; a so-called "scalar field", which would do the same; and modifications of Einstein's equations of gravity which would cause the expansion to accelerate at late times; but if you don't consider gravity a force, then neither would any of these (which are effects of gravity) be.

My point being, I'm not sure you're disagreeing with the current theories here, and if you are, then your ideas are so far not very well defined.

4. Matter initially expanded at about the same rate as space-time, but gravity and other forces emerged which caused matter to expand at a slower rate, and allowed stars and galaxies to form.
Matter expanded at the same rate as spacetime? What does that even mean? Matter's expansion is different from that of spacetime? Technically, matter doesn't expand at all - it's spacetime that expands, and matter that expands along with it. I'm guessing this is just a misunderstanding you have - if you're actually suggesting that the current theories are wrong and matter does have an expansion of its own, bear in mind that there's no evidence for such a thing and no basis in known physics, so you already have two strikes there ;)

5. Galaxies continued to expand away from each other, and the effects of gravity gradually decreased as the distance separating them increased.
Well... that's true... gravity between objects gets weaker as the distance between them expands...

6. And finally, galaxies began to separate at accelerating rates that more closely align with the ever accelerating expansion rate of space-time as the effects of gravity faded.
I'm really not sure what you mean here, except just "since the universe's expansion is accelerating, galaxies are accelerating from each other," which just about any scientist will tell you is clear.

Don't take this as hostility or my just parroting "This is not what is taught, therefore you are wrong." These are the immediate issues I see with the ideas you've put forth.
 
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arefin

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However, some galaxies are moving towards us like the Andromeda Galaxy.We are also moving towards a group of galaxies called the Local Group.
so if the universe weren't expanding, we'd see all the galaxies moving in the same direction - and at the same speed! Instead, we see them all moving in different directions (that is, whichever direction is away from us!) and at different speeds (the farther away, the faster the speed). Hope that helps.




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MeteorWayne

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Welcome to Space.com.

No it doesn't help, since you for some reason ignore the effect of gravity on small scales, such as galaxy clusters. That easily explains the local relative motion (such as the Andromeda galaxy) approaching us.

Basic physics....
 
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FlatEarth

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ramparts":128j0g62 said:
2. Expansion of space-time accelerates and has always accelerated.
This is certainly controversial - given what we know of the matter and radiation contents of the universe, in the past both of those should have dominated the universe's energy content (radiation for the first few hundred thousand years, then matter for the next few billion years). Because these things exert an attractive gravitational pull, both of those eras - the radiation-dominated era and matter-dominated era - almost certainly exhibited a decelerating expansion. In the next few years we'll be able to probe back and see what the expansion actually looked like during the matter-dominated era, but we're pretty sure that's what we'll see.
Space-time is being considered separate from energy and matter. We know the expansion of matter slowed following the initial expansion stage, however the thought is that perhaps space-time expanded at an accelerating rate from day one, and continues to regardless of how mass and energy move.

ramparts":128j0g62 said:
So you've made a claim just by stating it, without giving any backing or evidence, while science makes the opposite by using well-established physics to make a prediction from solid data. You may be right, but it's much, much more likely science is ;)
I'm using the same observations and the same physics, except I'm making a different conclusion. I don't believe there is a way to prove that space-time does not behave as I suggest.

ramparts":128j0g62 said:
3. The expansion of space-time is not driven by a force, but is analogous to gravity which is a distortion of space-time and not a force.
Well, if you're defining force that way, then there's no theory of dark energy which I know of which can be called a force. Various ideas include: a vacuum energy, whose gravitational effects would be repulsive; a so-called "scalar field", which would do the same; and modifications of Einstein's equations of gravity which would cause the expansion to accelerate at late times; but if you don't consider gravity a force, then neither would any of these (which are effects of gravity) be.

My point being, I'm not sure you're disagreeing with the current theories here, and if you are, then your ideas are so far not very well defined.
Those are energy theories. The point I'm trying to make is the expanding universe is the result of expanding space that is not energy driven.

ramparts":128j0g62 said:
4. Matter initially expanded at about the same rate as space-time, but gravity and other forces emerged which caused matter to expand at a slower rate, and allowed stars and galaxies to form.
Matter expanded at the same rate as spacetime? What does that even mean? Matter's expansion is different from that of spacetime? Technically, matter doesn't expand at all - it's spacetime that expands, and matter that expands along with it. I'm guessing this is just a misunderstanding you have - if you're actually suggesting that the current theories are wrong and matter does have an expansion of its own, bear in mind that there's no evidence for such a thing and no basis in known physics, so you already have two strikes there ;)
I don't mean to suggest matter itself expands. :roll: I'm saying the area of space occupied by matter expands at a different rate than space-time. You probably understand that by now. (The first two pitches were in the dirt, and I'm a high ball hitter. ;) )

ramparts":128j0g62 said:
5. Galaxies continued to expand away from each other, and the effects of gravity gradually decreased as the distance separating them increased.
Well... that's true... gravity between objects gets weaker as the distance between them expands...

6. And finally, galaxies began to separate at accelerating rates that more closely align with the ever accelerating expansion rate of space-time as the effects of gravity faded.
I'm really not sure what you mean here, except just "since the universe's expansion is accelerating, galaxies are accelerating from each other," which just about any scientist will tell you is clear.

Don't take this as hostility or my just parroting "This is not what is taught, therefore you are wrong." These are the immediate issues I see with the ideas you've put forth.
Now that perhaps you understand this concept better, maybe you can make a better analysis.
 
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ramparts

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FlatEarth":1rcaup8j said:
Space-time is being considered separate from energy and matter. We know the expansion of matter slowed following the initial expansion stage, however the thought is that perhaps space-time expanded at an accelerating rate from day one, and continues to regardless of how mass and energy move.
Hi FlatEarth. I'm not sure whose thought that is. Any time we talk about expansion, we talk about the expansion of spacetime. Consider matter as being stationary on that - any expansion it undergoes is the expansion of spacetime. Now, it's true, matter that's sufficiently close will attract each other and move contrary to the expansion - that's how galaxy clusters formed - but that's only on very small scales, not something that the large-scale distribution of matter does. On large scales, you can think of it as matter rearranging into a lumpy configuration, rather than matter contracting.

Also, as I said later in that post, no one things the expansion rate was accelerated from day one (within our universe), so again it's incorrect to say this is "the thought."

I'm using the same observations and the same physics, except I'm making a different conclusion. I don't believe there is a way to prove that space-time does not behave as I suggest.
It's impossible to prove a negative in physics. But if there's no evidence for a proposition, and no theoretical basis for it, then there's really no reason to believe it. I have yet to see any evidence for what you've been saying. But I haven't read the rest of this post yet...

ramparts":1rcaup8j said:
Well, if you're defining force that way, then there's no theory of dark energy which I know of which can be called a force. Various ideas include: a vacuum energy, whose gravitational effects would be repulsive; a so-called "scalar field", which would do the same; and modifications of Einstein's equations of gravity which would cause the expansion to accelerate at late times; but if you don't consider gravity a force, then neither would any of these (which are effects of gravity) be.

My point being, I'm not sure you're disagreeing with the current theories here, and if you are, then your ideas are so far not very well defined.
Those are energy theories. The point I'm trying to make is the expanding universe is the result of expanding space that is not energy driven.
What do you mean by "those are energy theories"? The vacuum energy theory involves an energy, of course, but invoking a scalar field doesn't, and modifying gravity certainly doesn't!

The other thing I'm still unclear on is what you are proposing, and how in particular it's different from an "energy driven" theory (bearing in mind that not all theories explaining the acceleration are "energy driven").

I don't mean to suggest matter itself expands. :roll: I'm saying the area of space occupied by matter expands at a different rate than space-time. You probably understand that by now. (The first two pitches were in the dirt, and I'm a high ball hitter. ;) )
Um, yes, this is true to a marginal extent. Where there is matter, that matter does indeed have an effect on the expansion of spacetime. But on large scales there are no areas of space with or without matter. The universe looks the same on cosmological scales. Anyway, I'm still not understanding your statement that: "Matter initially expanded at about the same rate as space-time, but gravity and other forces emerged which caused matter to expand at a slower rate, and allowed stars and galaxies to form."

Now that perhaps you understand this concept better, maybe you can make a better analysis.
I really don't. Your original post lacked in details on what you're proposing, and I asked questions trying to better understand that. Your response didn't really have any more details. There were 6 points originally. Point 1 was trivial. Point 2 we're disagreeing about the current scientific consensus, not about your ideas. Point 3 you alluded to your ideas being "not energy driven" without saying what your idea is. Point 4 you've said something that may or may not be right (depending what you mean) but was one sentence, and didn't say anything about your ideas. Points 5 and 6 you didn't respond to my replies (which were basically statements of confusion). I would recommend you lay out in a clear and concise (i.e. not overly wordy or rambly, short and sweet) fashion what you're getting at, rather than this little back and forth. Your first post wasn't specific enough, and that hasn't changed yet.
 
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FlatEarth

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ramparts, I'll go through the points again with more detail so it will hopefully be more clear.

1. Expansion of space-time was initiated at the BB and continues unabated.- The “continues unabated” part is not universally accepted. Expansion of space-time is commonly thought to vary through time, based on how galaxies have moved relative to each other.

2. Expansion of space-time accelerates and has always accelerated. - This assumption is the basis for the idea. Space-time is considered to be a measurement of size, distance, and movement (maybe this is an oversimplification, but you get the idea). I am treating space-time as a separate element that does not require the presence of mass or energy. So this statement means that only space-time (not matter-energy and space-time) always expanded at an accelerating rate.

3. The expansion of space-time is not driven by a force, but is analogous to gravity which is a distortion of space-time and not a force. - The point here is the expansion of space-time is an inherent property, not driven by energy.

4. Matter initially expanded at about the same rate as space-time, but gravity and other forces emerged which caused matter to expand at a slower rate, and allowed stars and galaxies to form. - As I've already stated, this does not mean matter itself expanded (although to a certain degree it did), only the distance separating matter. I'm referring to the initial expansion period here. While the expansion of the matter-energy region slowed, space-time continued to expand at the same accelerating rate, making the universe much larger than the matter-energy region. So, at this point in time onward, the universe has a combined matter-energy/space-time region, and an outer region of essentially only space or space-time (maybe with some subatomic particles).

5. Galaxies continued to expand away from each other, and the effects of gravity gradually decreased as the distance separating them increased. - This describes the period where galaxies were receeding from each other, but not at an accelerating rate due to the effects of gravity.

6. And finally, galaxies began to separate at accelerating rates that more closely align with the ever accelerating expansion rate of space-time as the effects of gravity faded. - The significance of this statement is, based on the hypothesis that space is expanding on its own and always has, galaxies that are not gravitationally bound to each other are now receeding at an accelerating rate.

I believe the concept of separating space-time from matter-energy may not have been clear, and caused the confusion. Please let me know if some of this still unclear.
 
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ramparts

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Hi FlatEarth,

That's a little clearer.... the problem is that your concept of separating matter/energy from spacetime as I understand it is something which doesn't jive with any of the known laws of physics. In fact, our equations (in particular the Friedmann equations, which are a solution of Einstein's equations of general relativity) are very clear about how spacetime's expansion is deeply coupled to the matter and energy in it. The idea of spacetime always acclerating while the matter doesn't goes completely against that. In fact, we know pretty much for a fact that in early times when either matter or radiation dominated the universe's energy content, spacetime was decelerating - this is an inevitable consequence of the Friedmann equations.

There's a problem for you. Another is: why would spacetime always be accelerating? What would be causing that acceleration? All you've said is that it's neither a force nor an energy. So what is it?
 
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FlatEarth

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ramparts":287nrx3h said:
Hi FlatEarth,

That's a little clearer.... the problem is that your concept of separating matter/energy from spacetime as I understand it is something which doesn't jive with any of the known laws of physics. In fact, our equations (in particular the Friedmann equations, which are a solution of Einstein's equations of general relativity) are very clear about how spacetime's expansion is deeply coupled to the matter and energy in it. The idea of spacetime always acclerating while the matter doesn't goes completely against that. In fact, we know pretty much for a fact that in early times when either matter or radiation dominated the universe's energy content, spacetime was decelerating - this is an inevitable consequence of the Friedmann equations.

There's a problem for you. Another is: why would spacetime always be accelerating? What would be causing that acceleration? All you've said is that it's neither a force nor an energy. So what is it?
Thanks, ramparts. Looks like I need to understand how something like space can be quantified so as to be included in an equation. :? What does it mean if Friedmann's equations are ignored? Isn't he dead anyway? ;) If you care to shed some light on this I would be interested.
Regarding the driver behind the expansion of space-time, the assumption is that it was initiated by the BB and it merely continues to behave as it always did. Why space expands is beyond our understanding, but we know it does.
 
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ramparts

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No problem :) It's great to be interested in this stuff. Friedmann's equations are the equations that relate the size and expansion of spacetime to its content by assuming two things: 1) that spacetime is homogeneous and isotropic (i.e., it looks the same everywhere) and 2) Einstein's equations of general relativity are correct. If either were found to be untrue on cosmological scales, that would be a huge coup - luckily, all the data so far suggest we're just fine :) By assuming that spacetime is the same everywhere and solving Einstein's equations, you get the Friedmann equations, and it's pretty easy to solve those in certain cases - for example, if the universe is dominated by matter (as it was early on), you can show the exact mathematical form of the expansion.
 
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FlatEarth

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ramparts":dkq2duey said:
No problem :) It's great to be interested in this stuff. Friedmann's equations are the equations that relate the size and expansion of spacetime to its content by assuming two things: 1) that spacetime is homogeneous and isotropic (i.e., it looks the same everywhere) and 2) Einstein's equations of general relativity are correct. If either were found to be untrue on cosmological scales, that would be a huge coup - luckily, all the data so far suggest we're just fine :) By assuming that spacetime is the same everywhere and solving Einstein's equations, you get the Friedmann equations, and it's pretty easy to solve those in certain cases - for example, if the universe is dominated by matter (as it was early on), you can show the exact mathematical form of the expansion.
This is fun to think about, and a good mind exercise. Your explanation helps my understanding, but as is usually the case, more understanding generally leads to more questions.

Suppose for a minute that the universe is indeed comprised of two zones. (I know this goes against what is generally accepted, but hang in there! ;) ) The primary zone is where we reside. It is just as you depict- homogeneous and isotropic, as described by Friedmann’s equations. The secondary zone is beyond the universe we know, and is essentially empty space with perhaps subatomic particles that escaped the effects of gravity. This zone is the result of space-time that expanded faster than the primary zone that is dominated by matter and gravity. Here Friedmann’s equations do not apply (I do not think), but the existence of an outer zone does not influence the primary inner zone in any way. It is devoid of energy and matter. The calculations for the evolution of the universe in the primary zone are unchanged.

I admit this is unprovable speculation on my part, but does it seem a bit more plausible to you?
 
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ramparts

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Well, I see two possibilities:

1) Our universe was always separate from your outside "zone", in which case it's pretty much irrelevant to physics and probably untestable. This is similar to what exists in some multiverse theories, in fact (actually, your idea - where the multiverse outside our universe is always expanding exponentially - is part of a well-thought of theoretical idea called eternal inflation). But this would do little to help us with our dark energy conundrum.

2) This zone separated from the rest of our universe because space expanded away from its matter. I think you've been suggesting this during this thread. This isn't allowed by the math. The two are coupled. If space expands, matter expands with it. When matter exerts a gravitational pull on other matter, it acts to slow down the expansion of spacetime. Perhaps you can define spacetime in a way in which that's not true, and I wouldn't argue with you, but then it wouldn't be spacetime with any particles, since those would follow the rest of the matter ;)
 
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FlatEarth

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ramparts":2sfknysu said:
Well, I see two possibilities:

1) Our universe was always separate from your outside "zone", in which case it's pretty much irrelevant to physics and probably untestable. This is similar to what exists in some multiverse theories, in fact (actually, your idea - where the multiverse outside our universe is always expanding exponentially - is part of a well-thought of theoretical idea called eternal inflation). But this would do little to help us with our dark energy conundrum.

2) This zone separated from the rest of our universe because space expanded away from its matter. I think you've been suggesting this during this thread. This isn't allowed by the math. The two are coupled. If space expands, matter expands with it. When matter exerts a gravitational pull on other matter, it acts to slow down the expansion of spacetime. Perhaps you can define spacetime in a way in which that's not true, and I wouldn't argue with you, but then it wouldn't be spacetime with any particles, since those would follow the rest of the matter ;)
I thought that was a good reply, ramparts. :)

The first scenario is certainly possible, but I’m trying to stay within the more narrow interpretation of the BB theory that treats our universe as the one and only. The point of this speculation is to offer an alternate solution to dark energy, so you are right.

I understand why space-time is considered dependent on mass, and the only person of consequence who believed it was not was Sir Isaac Newton! (And he didn’t know about GR!) The proven fact that a large mass bends space-time, and to an extreme degree will cause it to wrap it around itself, indicates that space-time is unlikely to expand unimpeded when matter is present. What was I thinking? :roll:

Let’s suppose this is what is happening instead. What if space-time would expand away from matter but cannot due to the effects of gravity. Instead, it extends beyond where matter is present by only a limited distance, and then wraps back on itself (similar in concept to what happens to a black hole, but on the scale of the universe, with nothing beyond). The expanding influence of space-time on matter is the same as proposed previously, but the result at the fringes of the universe is that space-time wraps back on itself instead of continuously expanding.

In your opinion, does this conflict with any established precepts?
 
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ramparts

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FlatEarth":in9ek69r said:
I thought that was a good reply, ramparts. :)

The first scenario is certainly possible, but I’m trying to stay within the more narrow interpretation of the BB theory that treats our universe as the one and only. The point of this speculation is to offer an alternate solution to dark energy, so you are right.
Well, the theorists I know are actually pretty big supporters of eternal inflation. The big bang doesn't require our universe to be the one and only, it just ignores the question.

I understand why space-time is considered dependent on mass, and the only person of consequence who believed it was not was Sir Isaac Newton! (And he didn’t know about GR!) The proven fact that a large mass bends space-time, and to an extreme degree will cause it to wrap it around itself, indicates that space-time is unlikely to expand unimpeded when matter is present. What was I thinking? :roll:

Let’s suppose this is what is happening instead. What if space-time would expand away from matter but cannot due to the effects of gravity. Instead, it extends beyond where matter is present by only a limited distance, and then wraps back on itself (similar in concept to what happens to a black hole, but on the scale of the universe, with nothing beyond). The expanding influence of space-time on matter is the same as proposed previously, but the result at the fringes of the universe is that space-time wraps back on itself instead of continuously expanding.

In your opinion, does this conflict with any established precepts?
You're getting pretty far beyond our established precepts here, by speaking of spacetime as an independent "thing" which can move away from the matter and energy it carries. This is not at all necessary for GR and, again, there's no way to fit it into the math. So it's possible, but we have neither observational evidence nor theoretical support, so there's not much point in it :)
 
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FlatEarth

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ramparts":2l65rb3u said:
You're getting pretty far beyond our established precepts here, by speaking of spacetime as an independent "thing" which can move away from the matter and energy it carries. This is not at all necessary for GR and, again, there's no way to fit it into the math. So it's possible, but we have neither observational evidence nor theoretical support, so there's not much point in it :)
Definitely this is a different interpretation of what is observed, but it is consistent with observations that have been made, and I think it preserves most of what we have come to accept as true. As you said, there is no way to fit it into the math, but I think that also means it does not violate the math. I personally believe that in the case of space-time, scientists have given it properties that may not be completely correct. It seems there is a point in rethinking space-time to help answer some of the unexpected observations that have been made.

Cheers. :)
 
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