Everything's expanding... well no, actually.
Discussion
I'm fairly sure the general expansion of the universe doesn't preclude two arbitrary objects from moving towards each other. There are plenty of simple mechanisms that enable it. It is a generalised observation on the highest of macro scales.
The balloon analogy shows the danger of using simple metaphors to explain deep and rather complicated concepts. This doesn't mean that they don't have validity, just that the limit of the abstracted model must be borne in mind.
So far as is known, wherever you stand in the universe, the rest of it appears to recede. This makes it look like the big bang started wherever the observation point is. Anyway, if it isn't expanding, where are all those extra wavelengths of light going to?
The balloon analogy shows the danger of using simple metaphors to explain deep and rather complicated concepts. This doesn't mean that they don't have validity, just that the limit of the abstracted model must be borne in mind.
So far as is known, wherever you stand in the universe, the rest of it appears to recede. This makes it look like the big bang started wherever the observation point is. Anyway, if it isn't expanding, where are all those extra wavelengths of light going to?
Gene Vincent said:
BenM77 said:
Interesting thread, so is it still believed that our galaxy is moving away from the big bang ?
We might be.But that local Andromeda blue-shift could mean that we are either in stasis or moving toward it and this might mean we have 'countered' our own 'personal' expansion from the BB.
BenM77 said:
I have seen the explanation that looks like we are the centre of the big bang but are not, perhaps blue shift and red shift could help work where the centre is ? This will probably sound very dumb
Not in the least dumb.In maths we have the 'Cosmological Principle' and this simply states that the Cosmos looks the same from everywhere, not the position of the stars, but the recession of the stars from your viewpoint (Isotropy and Homogeneity) it's a bold statement to make but it has recently been reinforced by the detailed understanding of the CMBR (Cosmic Microwave Background Radiation)
We can safely take the CP as being correct.
Observation can't tell us enough to be conclusive that the Cosmos is either infinite and expanding/contracting or that it is simply finite and expanding, we need maths...
We have to use Einsteins GR to do this and the results are at first sight inconclusive, thanks to GR being perhaps the most tested of all the theories we've ever had it could be either... but there is a little final issue when you take the maths apart in detail, if the Cosmos were infinite then not only would every point be the same viewpoint as far as expansion is concerned but it means that each observers local cluster point cannot move and this detail is what kills the possibility of the Cosmos being infinite. Our local cluster moves!
BTW, a further nail in coffin of time having a substantive existence all of its own is that if you apply the CP to all four dimensions, you get no big bang, it applies only to the space bit of spacetime.
Bedazzled said:
From what I've read everything is expanding, but objects which are bound either gravitationally or atomically 'bounce back' into their natural position, at least while those forces are stronger than the force of expansion. So for example the planets in our solar system adjust their orbit to compensate for expansion; but expansion occurs locally all the same.
If the force of expansion continues to increase then it could theoretically overcome gravity causing gravitationally bound objects fly apart, or even overcome atomic forces causing atoms to fly apart (according to Lawrence Krauss, in his famous "a universe from nothing" presentation). It's a moot point unless we get to the bottom of what causes expansion in the first place, and what is likely to happen to the magnitude of the repulsive force in the future.
The intriguing mystery for me is how such a force could cause the dramatic inflationary period after the big bang, and how at this very moment distant galaxies with redshifts greater than 1.4 are moving away from us faster than light.
Gravity is the most pervasive of all the parts that make up the Cosmos, there is no 'bounce back' just constant check-mate.If the force of expansion continues to increase then it could theoretically overcome gravity causing gravitationally bound objects fly apart, or even overcome atomic forces causing atoms to fly apart (according to Lawrence Krauss, in his famous "a universe from nothing" presentation). It's a moot point unless we get to the bottom of what causes expansion in the first place, and what is likely to happen to the magnitude of the repulsive force in the future.
The intriguing mystery for me is how such a force could cause the dramatic inflationary period after the big bang, and how at this very moment distant galaxies with redshifts greater than 1.4 are moving away from us faster than light.
The increase in the force of expansion will most likely be self-immolating in that the increased distances between objects will allow this to happen without any adverse effect.
A sort of 8pi^2 equilibrium.
They WERE moving apart at faster than light, they won't be now, the inflationary period was a very long time ago.
Edited by Gene Vincent on Wednesday 22 August 20:42
Bedazzled said:
Gene Vincent said:
There WERE moving apart at faster than light, they won't be now, the inflationary period was a very long time ago.
Have a play around with the cosmos calculator here (I'm using omega=0.27, lamda=0.7, hubble=70). The light reaching us from a galaxy with a redshift of 1.4 was emitted 4.6 billion years after the big bang; well after the inflationary period which lasted only a fraction of a second. We've observed galaxies with redshifts of 8.6 which are moving away from us at over twice the speed of light.But my guess is that the '70' is todays Hubble Constant (actually 71 if so) but the 'constant' is no such thing, in the past, into which you are looking, it was markedly different.
Plus does the link calculate all three main shift mechanisms?
I don't trust 'applications' from whatever source, I'll do the maths myself, I feel happier.
Bedazzled said:
They all give the same answer... galaxies with a redshift > 1.4 are moving away faster than c. The question is, how?
Are they really moving away at a speed greater than c, in the sense that they are moving though space/time at a speed greater than c; or rather, is space/time itself between us and those galaxies expanding at a rate greater than c?Greg66 said:
Bedazzled said:
They all give the same answer... galaxies with a redshift > 1.4 are moving away faster than c. The question is, how?
Are they really moving away at a speed greater than c, in the sense that they are moving though space/time at a speed greater than c; or rather, is space/time itself between us and those galaxies expanding at a rate greater than c?MiseryStreak said:
Greg66 said:
Bedazzled said:
They all give the same answer... galaxies with a redshift > 1.4 are moving away faster than c. The question is, how?
Are they really moving away at a speed greater than c, in the sense that they are moving though space/time at a speed greater than c; or rather, is space/time itself between us and those galaxies expanding at a rate greater than c?I also assumed that the expansion of space/time was the reason why galaxies are moving apart at faster that the speed of light. (Based on the fact that matter cannot exceed that speed, and the everything in the galaxy cannot all be heading away from us at impossible speed.)
Sorry, been working.
I think there might be a fundamental misunderstanding of this entire expansion concept.
So, to get us back on track I'll briefly re-iterate what we know happens as related in this thread.
1/. The Cosmos is expanding.
2/. There are bits of this Cosmos we can see and although they are in the sway of the overall expansion mechanism, they themselves, thanks to their own gravity, don't expand.
3/. These visible entities also have extensive gravity fields and these extend hugely beyond their visible extent.
Thus far we've kept things simple.
Now we have the hard bit.
The reality is that although the expansion is quantified and the truth is the expansion of space has no speed.
You have to accept that the best manner in which to think of the expansion of space is as the creation of new empty space.
That is what an Expanding Cosmos really does.
I know you've all grown up with first the 'universe' expanded at the speed of light, then you were told there was this 'inflationary' period and we went back to the speed of light thing, well it's not correct, the inflationary bit is (but even that doesn't work quite as you might believe) but we didn't go back to the speed of light expansion.
The Cosmos today, as we speak is expanding far faster than the speed of light.
I know... this is a bitter thing to find out, but I'm not Mary Poppins, you're getting no spoonful of sugar from me.
Empty space... out there between the GEBs 'new' space is produced, in varying amounts, 1 or 2 parts per million and instantly too.
This is enough to cause the entire Cosmos (remembering the GEBs don't in themselves) to expand in size faster than light... but nothing is actually moving.
Someone much smarter than me, and much nicer too, once said something like "if you think you understand something fundamental in this Cosmos, then you simply haven't understood at all"
The above will test your powers of understanding to the limit.
I think there might be a fundamental misunderstanding of this entire expansion concept.
So, to get us back on track I'll briefly re-iterate what we know happens as related in this thread.
1/. The Cosmos is expanding.
2/. There are bits of this Cosmos we can see and although they are in the sway of the overall expansion mechanism, they themselves, thanks to their own gravity, don't expand.
3/. These visible entities also have extensive gravity fields and these extend hugely beyond their visible extent.
Thus far we've kept things simple.
Now we have the hard bit.
The reality is that although the expansion is quantified and the truth is the expansion of space has no speed.
You have to accept that the best manner in which to think of the expansion of space is as the creation of new empty space.
That is what an Expanding Cosmos really does.
I know you've all grown up with first the 'universe' expanded at the speed of light, then you were told there was this 'inflationary' period and we went back to the speed of light thing, well it's not correct, the inflationary bit is (but even that doesn't work quite as you might believe) but we didn't go back to the speed of light expansion.
The Cosmos today, as we speak is expanding far faster than the speed of light.
I know... this is a bitter thing to find out, but I'm not Mary Poppins, you're getting no spoonful of sugar from me.
Empty space... out there between the GEBs 'new' space is produced, in varying amounts, 1 or 2 parts per million and instantly too.
This is enough to cause the entire Cosmos (remembering the GEBs don't in themselves) to expand in size faster than light... but nothing is actually moving.
Someone much smarter than me, and much nicer too, once said something like "if you think you understand something fundamental in this Cosmos, then you simply haven't understood at all"
The above will test your powers of understanding to the limit.
Edited by Gene Vincent on Thursday 23 August 20:03
EliseNick said:
What is a "Gravitational Extent Boundary"? It obviously doesn't look like a conventional event horizon. Google just sent me... back to this thread! When you say "correctly called a GEB", correct in what sense?
The Suns 'local' GEB has within it our planet and the others... but it extends out much further than that.EliseNick said:
What is a "Gravitational Extent Boundary"? It obviously doesn't look like a conventional event horizon. Google just sent me... back to this thread! When you say "correctly called a GEB", correct in what sense?
I thought I'd explained the phenomena earlier."Most people will know that mass concentrates gravity at its centre and the greater the mass the greater the gravitation that permeates from it and it is these gravity wells and all contained within them that does not expand, there is an 'event horizon' surrounding every Galaxy in the Cosmos, that event horizon is correctly called a Gravitational Extent Boundary and is the point where gravity and Cosmological expansion are equal... the extent of some Galaxies GEB is enormous."
Forget the Sun analogy as in reality it doesn't really have a GEB in the terms we are using in this thread.
For a moment I thought I'd not explained this...
EliseNick said:
What is a "Gravitational Extent Boundary"? It obviously doesn't look like a conventional event horizon. Google just sent me... back to this thread! When you say "correctly called a GEB", correct in what sense?
As I understand (hmm. Really?) GV's point, it is this:A galaxy exerts an attractive gravitational force on its surroundings. Cosmological "expansion" (perhaps a misleading word) - see below exerts a counterveiling force, in that things should get further apart.
The GEB is the (curved) plane lying outside a galaxy at which the attractive gravitiional force exerted by the galaxy is precisely matched by the force of cosmological expansion. Stuff inside the GEB is drawn to the galaxy. Stuff outside it isn't.
Consider two galaxies with a distance between their respective GEBs. GV's point is that the space between the GEBs is not expanding in the commonly used sense of the word "expanding". Instead, new space is being created instantly adding to the existing space. So, if you were to lay 12" rulers end to end between the two GEBs, they would not be expanding to 13", then 14” and so on. Instead you would have to imagine new 12” rulers instantly coming into existence between the two GEBS, increasing the total number of rulers between the GEBs.
And that, I think, is the point he is making about what "expansion of space" really should be understood to mean.
Whether it's right or wrong, I have no idea; ditto its significance.
Gene Vincent said:
I thought I'd explained the phenomena earlier.
"Most people will know that mass concentrates gravity at its centre and the greater the mass the greater the gravitation that permeates from it and it is these gravity wells and all contained within them that does not expand, there is an 'event horizon' surrounding every Galaxy in the Cosmos, that event horizon is correctly called a Gravitational Extent Boundary and is the point where gravity and Cosmological expansion are equal... the extent of some Galaxies GEB is enormous."
Forget the Sun analogy as in reality it doesn't really have a GEB in the terms we are using in this thread.
For a moment I thought I'd not explained this...
Why does the Sun not have one, but a galaxy does? Is there some threshold mass?"Most people will know that mass concentrates gravity at its centre and the greater the mass the greater the gravitation that permeates from it and it is these gravity wells and all contained within them that does not expand, there is an 'event horizon' surrounding every Galaxy in the Cosmos, that event horizon is correctly called a Gravitational Extent Boundary and is the point where gravity and Cosmological expansion are equal... the extent of some Galaxies GEB is enormous."
Forget the Sun analogy as in reality it doesn't really have a GEB in the terms we are using in this thread.
For a moment I thought I'd not explained this...
Can you write down an equation defining the surface you are terming the GEB for a given mass distribution?
EliseNick said:
Gene Vincent said:
I thought I'd explained the phenomena earlier.
"Most people will know that mass concentrates gravity at its centre and the greater the mass the greater the gravitation that permeates from it and it is these gravity wells and all contained within them that does not expand, there is an 'event horizon' surrounding every Galaxy in the Cosmos, that event horizon is correctly called a Gravitational Extent Boundary and is the point where gravity and Cosmological expansion are equal... the extent of some Galaxies GEB is enormous."
Forget the Sun analogy as in reality it doesn't really have a GEB in the terms we are using in this thread.
For a moment I thought I'd not explained this...
Why does the Sun not have one, but a galaxy does? Is there some threshold mass?"Most people will know that mass concentrates gravity at its centre and the greater the mass the greater the gravitation that permeates from it and it is these gravity wells and all contained within them that does not expand, there is an 'event horizon' surrounding every Galaxy in the Cosmos, that event horizon is correctly called a Gravitational Extent Boundary and is the point where gravity and Cosmological expansion are equal... the extent of some Galaxies GEB is enormous."
Forget the Sun analogy as in reality it doesn't really have a GEB in the terms we are using in this thread.
For a moment I thought I'd not explained this...
Can you write down an equation defining the surface you are terming the GEB for a given mass distribution?
Our star is part of a greater gravitational mass.
It's not a surface, it is an extent of influence.
Somewhere on here I have given a figure for the minimum distance between massive objects for the influence of gravity to diminish to a point where expansion can act.
I'll take a look tomorrow or find my notes at work and post it up again.
Gene Vincent said:
Because a 'boundary' isn't present as far as the context of expansion is concerned.
Our star is part of a greater gravitational mass.
It's not a surface, it is an extent of influence.
Somewhere on here I have given a figure for the minimum distance between massive objects for the influence of gravity to diminish to a point where expansion can act.
I'll take a look tomorrow or find my notes at work and post it up again.
So is it a distance? Or a volume? I still don't understand what it actually is. Suppose I could flick a switch and make our galaxy's GEB glow bright orange. What would I see if I stood on Earth and looked into the sky? If I was in the Andromeda Galaxy? If I was in the Virgo Cluster?Our star is part of a greater gravitational mass.
It's not a surface, it is an extent of influence.
Somewhere on here I have given a figure for the minimum distance between massive objects for the influence of gravity to diminish to a point where expansion can act.
I'll take a look tomorrow or find my notes at work and post it up again.
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