Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Bill S on 30/07/2017 02:42:10
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Certainly, a common image is that of an expanding sphere, like an inflating balloon. This, of course, is not to be confused with the “balloon analogy” in which the Universe is represented by the two-dimensional surface, rather than by the whole balloon.
Let’s think briefly about this visualisation. Without in any way suggesting that the Universe actually has a physical boundary, the mental image will almost certainly have one. You, of course, will be at the centre of this sphere, and will see the rest of the Universe moving away from you. The most up to date figure for the expansion rate of the Universe is “67.3 kilometres per second per megaparsec”. (A megaparsec is defined as a distance equal to 3.26 million light years.)
Just to make the arithmetic easy, let’s say our imaginary sphere has a radius of one thousand megaparsecs. Obviously, this is much too small, but it is just a simple thought experiment. This means that the imaginary boundary will be separating from you at 67,300 kilometres per second. The galaxies are being carried along with the expanding space, so any celestial body that is within the last 67,300 km. on this side of the boundary now, will be outside the present boundary position in one second’s time. It will be in newly created space; space that was not there a second ago; at least, it will be if the expansion of the Universe really does involve the constant creation of new space.
Think a little more about this, though. An observer, say, on a planet that has, from your perspective, just passed into the newly created space, will perceive himself as being at the centre of a spherical universe, and will think that you have just passed into newly created space.
This tells us a couple of things:
(1) If the Universe is homogeneous, and in order to do any meaningful cosmology we must assume it is, we cannot define a physical boundary.
(2) We cannot define any part of the Universe; rather than any other part; as being the newly created part. This must mean that every part of the Universe is expanding: new space is coming into existence everywhere in the Universe, all the time. No part is newer than any other part. Newness is relative!
I would welcome comments on these random thoughts.
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1 makes sense to me although you might be able to argue that just as with a balloon there always will be a boundary on which we are 'stuck', or 'inside'.
2 too.
It's a matter of what perspective you use, with the 'eyes of a God', presuming 'it' to be able to perceive everything instantly, everything must happen at a 'same time'. No 'patches of space' can be newer, due to distance etc.
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One can imagine an infinite 3D array of points in a crystalline lattice. No boundaries, but you can only see so far from any particular point. This lattice can expand or contract in many ways (depending on the symmetry of the lattice, there could be unique axes along which it could dilate independently (some would not be orthogonal).
As far as I know, the cosmos is not crystalline, in terms of where the matter is. But because it is "uniform" on a large enough scale, we can consider that to define the "unit cell" of our mental crystal.
cubic lattice: http://gph.is/1e5hi7F
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Consider a lattice where the cubes are replaced by spheres that all expand at the same rate. They will appear to expand at different rates the further they are away from the observer. Just think about that for a moment. The distances between spheres will appear smaller the further away they are. Since they will have expanded less in the past. Isn't this the opposite of what we see with the current state of the universe?
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Consider a lattice where the cubes are replaced by spheres that all expand at the same rate. They will appear to expand at different rates the further they are away from the observer. Just think about that for a moment. The distances between spheres will appear smaller the further away they are. Since they will have expanded less in the past. Isn't this the opposite of what we see with the current state of the universe?
I'm not sure what you mean by "they will have expanded less in the past" ... In both the real world and in the model more distant observations would necessarily be of older events (speed of light and all).
This lattice model accounts for the increasing red-shift of increasingly distant objects, if that's what you mean (if all cubes or spheres are expanding at the same rate, longer distances will grow faster than shorter ones.)
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Ok so say the profile circumference of each sphere is detectable. Then the redshift tells us at what distance each successive sphere was when the light left it. We can then determine that spheres were smaller in the past. All well and good so far. However this would not reflect what Hubble found. Am I missing something?
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Just to stir the pot a little. As the mass density required to create a black hole falls with increasing mass then the whole universe could be within its own event horizon. Yet all the mass doesn't form a singularity. It is actually expanding.
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I'll stir the pot too :)
Do you mean expanding 'inside' or 'outside'?
Who's the 'observer'?
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I'll stir the pot too :)
Do you mean expanding 'inside' or 'outside'?
Who's the 'observer'?
That is a very good question. I am currently in a cinema coffee shop so I will make a better reply later.
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Thanks for the comments, folks. There’s quite a bit to think about there.
A related thought towards which I was drifting was this:
If the surface of last scattering is the furthest back we can “look” in terms of the age of the Universe; then whenever we look towards it, we are looking towards the Big Bang.
Every direction in which we look is towards the surface of last scattering, and therefore towards the BB. This will apply to observations made from any, and every, point in the Universe.
Is this a reasonable response to the question as to where the BB happened?
It seems to establish conclusively that it must have happened everywhere.
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presuming 'it' to be able to perceive everything instantly, everything must happen at a 'same time'.
If everything happens simultaneously, time is not involved; everything simply “is”. Surely. This would describe infinity/eternity. (?)
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I'll stir the pot too :)
Do you mean expanding 'inside' or 'outside'?
Who's the 'observer'?
We are the observers, we stand between above & below
I see this universe, as a quark within a proton, (proton = multiverse), meaning we are walking talking, multi-versal entities.
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I'll stir the pot too :)
Do you mean expanding 'inside' or 'outside'?
Who's the 'observer'?
I am going to revisit my book on galaxy formation. There are some views of the early universe that are surprising.
https://www.space.com/866-surprising-view-early-universe.html
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Just to make the arithmetic easy, let’s say our imaginary sphere has a radius of one thousand megaparsecs. Obviously, this is much too small, but it is just a simple thought experiment. This means that the imaginary boundary will be separating from you at 67,300 kilometres per second. The galaxies are being carried along with the expanding space, so any celestial body that is within the last 67,300 km. on this side of the boundary now, will be outside the present boundary position in one second’s time. It will be in newly created space; space that was not there a second ago; at least, it will be if the expansion of the Universe really does involve the constant creation of new space.
I suppose the last sentence would be correct if, and only if, new space were being created only at what we might consider, from our individual perspective, to be a boundary. On reflection, such seems unlikely, because each, and every, observer sees a boundary in a different place.
However, this means that if, potentially, there is an observer at every point in the Universe, there must be a perceived boundary at every point, also. Therefore, if new space is being created at "the boundary", it is being created everywhere in the Universe, so no part can be defined as newer than any other.
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We can equate new space with new vacuum. Since the vacuum can be considered to be a condensate then this is fine. Since adding or removing from a condensate doesn't change the condensate. It just gets bigger.
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OK; but the question still remains: does new vacuum appear everywhere; i.e. uniformly across the Universe?
To this is now added: What happens to the vacuum energy when new vacuum is created?
1. Is preexisting vacuum energy diluted?
2. Does the new vacuum come with its own vacuum energy?
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OK; but the question still remains: does new vacuum appear everywhere; i.e. uniformly across the Universe?
To this is now added: What happens to the vacuum energy when new vacuum is created?
1. Is preexisting vacuum energy diluted?
2. Does the new vacuum come with its own vacuum energy?
The vacuum shouldn't change. That is the nature of a condensate. What exactly is the sum of all the vacuum energy? That is a good question to research.
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The vacuum shouldn't change. That is the nature of a condensate.
If new space is created which has lower vacuum energy than pre-existing space, would that not change “the vacuum”?
What exactly is the sum of all the vacuum energy? That is a good question to research.
Run away! :)
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You would still have the same amount of vacuum energy. That is why people think they can get free energy from it. They can't.
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One problem that I see with this visualization and others similar ones for the expansion of the universe, is connected to time dilation experiments. For example, with a moving clock, there will be a permanent change in time that we can measure. However, when you investigate the clock after the experiment the clock does not show a permanent change in size or distance. The size change was more of a reversible mirage.
In the twin paradox, one twin will have age slower. However, no where is it said the slower aging twin will also remain shorter or thinner due to the motion. The distance contraction is inferred by the light we see. However, it does not persist when we examine the matter. Only time change is permanent.
What this tells me is that time is the dynamic variable and distance is a passive variable. We measure the universe based on its energy/light. We cannot directly measure the matter, but have to infer its properties from energy. With time the dynamic and permanent variable, it makes more sense that the frequency of the energy will show a permanent change. The passive wavelength is carried along, since the product of wavelength and frequency has to remain constant; speed of light. With matter, like two twins, distance and time do not have to multiple to a constant so only time will change, while distance does nothing permanent, when we examine both after the experiment is over. We are confusing a dynamic time shift with motion induced Doppler shift, due to using second hand light data to define the state of the matter, Has any direct matter experiment even been done that shows a permanent change in distance or size? We can take two boxes which are exactly 1 meter cubes.
The bias of tradition calls the relationship between time and space, space-time, placing distance before time. But this is not what we see when you run experiments with matter. Time should have top billing. It should be called time-space to set the mind properly in terms of what is the permanent change in the material systems, which give off the energy, by which we infer.
In time-space there are four dimensions of time. There is 0-D, 1-D, 2-D and 3-D time. 0-D time is a point in time such as taken with a photo snap shot. 1-D time is a time line such as connected to velocity; d/t and special relativity. 2-D time is connected to acceleration and therefore all the forces; d/t/t. While 3-D is an acceleration of an acceleration; d/t/t/t. This is connected to the apparent accelerated expansion of the universe in spite of the acceleration due to gravity. What we appear to see is connected to 3-D time leading energy via wavelength.
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@puppypower Time only flows in one direction so that dilation of time has to be permanent. Space on the other hand has no such limitations within an inertial frame of reference.
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Time only flows in one direction so that dilation of time has to be permanent. Space on the other hand has no such limitations within an inertial frame of reference.
This works with both "tensed" and "tensless" time. I am inclined to go with tensed time, but that's just a personal thing.
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Isn't a (perfect) vacuum primarily a expression of a geometry? Does it 'exist' without a geometry being present?
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turn it around.
Does a vacuum demand a geometry?
Can a geometry exist without it?
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Does it 'exist' without a geometry being present?
It depends, to a great extent, on what you mean by a perfect vacuum. How do you distinguish between that and “nothing”?
Also; what do you mean by “a geometry”? Is it something that exists in/of itself; or is it a mathematical tool that has relevance only in human calculations?
I’ll not even ask what you mean by “exist”; I think that’s been thrashed to death elsewhere, without any real conclusions being reached.
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Another thing is the cosmological constant problem and the value of the density parameter. I am off shopping now but will continue later.
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Just a little light reading.
https://profmattstrassler.com/articles-and-posts/particle-physics-basics/quantum-fluctuations-and-their-energy/
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Thanks for the link; I read this some time ago, but it is certainly worth another look. Hopefully my understanding will have improved.
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A perfect vacuum is a ideal vacuum. As you say a vacuum is defined by it being 'nothing' generally speaking. And a geometry is mathematics describing points curves 'surfaces' etc. We have four dimensions, and as I see it they are (define) the geometry in which we exist.
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So, what came first :)
The geometry, or the vacuum?
In other words, is the geometry we find a result of a existing vacuum, or is a vacuum a result of a existing geometry?
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We have fermions and bosons. Fermions exclude each other, aka, takes up a privileged 'place', that's matter. Bosons, including photons, don't, you can super impose them as much as you like. The Big Bang is thought to be a result of highly energetic bosons, decaying into fermions. And it's about energy.
Let's presume that the energy inside a SpaceTime doesn't get refilled. As soon as there is a Big Bang the energy has some finite magnitude. Then you have one amount to play with. But the universe is expanding.
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On the very small plane, using QM, you have indeterminacy. It's about the probability of something to become/happen, and there we find statistics telling us how it mostly acts. Then we have the idea of energy in a vacuum, suggesting that it relative time can be of a 'infinite magnitude'. If we now treat the universe as having a 'boundary' of some sort, which we must if the idea of a defined amount of energy exists, then a expansion should 'dilute' this energy, shouldn't it? If it does it should be noticeable.
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That is, depending on what we think this 'geometry' is about. How it comes to be.
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Add to that that the idea seems to be that the universe is in a equilibrium, energy wise. meaning that we don't expect one patch of space to differ from another. It doesn't matter if the vacuum expands. We expect a homogeneous and isotropic universe to exist in all possible means, including energy distribution. identical rocks containing the same amount of energy etc.
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Then we have the idea of 'emergences'. When something gains properties very difficult/impossible to foresee from its origins. https://en.wikipedia.org/wiki/Emergence
That gives us some questions
1 if the Big Bang is a emergence, will it still have a 'boundary'?
2 what is 'c'
'c' is more than just a speed, it's also information. And in a expansion, presuming it to become in each 'point' of a universe equally, it also becomes a question of how 'fast' the new 'patch' gets acknowledged by 'c', and that you might be able to relate to a 'possible size' of new 'patches'
Treating it this way we becomes a 'fault' in something else, and we can still presume a equilibrium to exist, a boundary existing, or not. The 'boundary' in this case solely related to the emergence of new properties, and as we can't place ourselves outside SpaceTime there should be no end to it.
It also allow us to think of the surface of that balloon in a new way. It's here, coexisting with what isn't 'here', inside a SpaceTime.
And then we have 'time'. The one way arrow, that some ideas expect to become fuzzy as you 'wind history backwards', in a similar way to how we can find indeterminacy existing. I connect it to 'c' myself so if that is true then 'c' also should lose its properties looking backward. I don't expect that to be true myself, time is outcomes and to change outcomes I think you will need different 'universes/splits'.
And yes, the way I think of it geometry is a property too. It has to be, considering LorentzFitzgerald contractions, and of course 'time dilation's'. All of it properties of a 'whole universe', whereas our local definitions indeed becomes a 'golden standard' from where we find those existing.
In the end it relates to how you make your repeatable experiments, proving physics consistency in time and space. You do them locally.
Let's end with this. Defining a Big Bang as a emergence, and so also a expansion, it should mean that this still is a ongoing process, The Big Bang is still here. What it leaves me to ask is about time. Is time a result of a SpaceTime existing, that means, a 'property'?
There is another way to describe a Big Bang, as 'symmetry break(s)'. But applied on what happens inside as it 'cools'.
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… As you say a vacuum is defined by it being 'nothing' generally speaking.
“generally speaking”? Under what conditions would “nothing” be “something”/
And a geometry is mathematics describing points curves 'surfaces' etc.
If a vacuum is defined by it being 'nothing', it can have none of these properties.
We have four dimensions, and as I see it they are (define) the geometry in which we exist.
That has to be the geometry of spacetime; not the geometry of nothing.
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So, what came first :) The geometry, or the vacuum?
If the vacuum is nothing; it didn’t “come”, or do anything else.
In other words, is the geometry we find a result of a existing vacuum, or is a vacuum a result of a existing geometry?
Nothing can be the result of “nothing”, so the geometry cannot arise from the vacuum. Nor can the vacuum arise from the geometry, or from anything else.
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The Big Bang is thought to be a result of highly energetic bosons, decaying into fermions. And it's about energy.
I’ve no problem with that idea, but where does an “absolute vacuum”, or “absolutely nothing” fit in?
Let's presume that the energy inside a SpaceTime doesn't get refilled. As soon as there is a Big Bang the energy has some finite magnitude. Then you have one amount to play with. But the universe is expanding.
Are you saying that, before the BB, energy was infinite?
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"Under what conditions would “nothing” be “something”/"
Depends on how you define a vacuum. If you think of it as a 'field' containing 'energy' aka 'virtual particles' then even a 'perfect vacuum' is 'something'. But if we ignore that interpretation then what's not there, is not there. I'm not being partial here, it's more of a question of how you look at it.
"If a vacuum is defined by it being 'nothing', it can have none of these properties." Well, it does have those properties, the vacuum is also called space and space 'bends' etc. It actually needs a geometry to exist, well, as I see it then.
and yes, I agree, it's the geometry of SpaceTime, although not including 'time' in this question.
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"Are you saying that, before the BB, energy was infinite?"
I'm doing none of that. What was, or is, 'behind' a Big Bang is as far as I know unmeasurable. What we have is 'energy', and there is no simple definition of it more than the idea that everything we know of is presumed to have a relation to it. Or comes from 'it'. That's also one of the things I'm wondering about
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Actually physics doesn't cover the way we found out about it. Using logic, mathematics etc, all demand something 'thinking' and 'testing'. And to define what a thought is, isn't covered by physics although it is the origin of everything we ever wondered about.
There is one important point though. Presuming a vacuum to be nothing but still giving us an appearance (observer dependent), what would make it 'exist'? In such a case, to me, the geometry of our universe becomes interesting, and with it my original question(s).
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In fact, if you now equal a vacuum with 'energy' as in some 'zero point energy' you meet problems. Then again, even when equaling a vacuum to some 'energy holding field' possibly, we still can question whether this is a 'finite' resource created at a Big Bang. That, on the other tentacle, may not be equivalent to suggesting this energy as being in a equilibrium.
If we assume that the 'energy' is in a equilibrium, which I tend to do, meaning that the universe is isotropic and homogeneous att all 'patches', be they matter or a vacuum. Then the question becomes how that is possible, From where, if so, does the universe 'lend/gain' the energy to fill an expansion? Maybe it doesn't need to, though? That something is unmeasurable do not state that it can't be.
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One could see it this way. You are always inside a SpaceTime, the measurements made also inside, the 'forces' we define too. Now follow that thinking to its logical conclusion. Also you need to consider whether a 'field' is observer dependent too. 'Space' definitely is, including matter.
Let's take a example, two observers accelerating from Earth gaining different uniform motions following the same direction will define two distances, to some agreed on object (some sun). If now the 'vacuum energy' is measured to be equivalent with what they expected before the acceleration by both, according to their instruments, although the distance(s) has shrunk/contracted, who is right? Actually we have three possibilities here, the one they shared on Earth, and the definition they now have relative their own 'patch of contracted space'
If you want you can even ask yourself whether you think 'energy' too is observer dependent.
As far as I get it, it is.
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Then consolidate this with the universe being in a equilibrium, which I definitely expect it to be. It's a lovely headache :)
What is not observer dependent here is their local measurements. Doing the experiments in 'black boxes', not knowing anything about the situation relative other objects they should come to an agreement, as they all are in a uniform motion.
Another thing to notice is that although 'space' has contracted for both relative earth, none of them will find a 'increase in energy' via for example some casimir experiment (Casimir–Polder force).
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Let's try this. 'What is the energy density of a vacuum' by John Baez
http://math.ucr.edu/home/baez/vacuum.html
Ps: it's worth following the links if you want to see the ideas about a 'negative pressure' explained in a straightforward manner.
Furthermore, it doesn't change the question of what a 'vacuum' is, it gives you a explanation through GR of how it is thought to work (a expansion), but does not answer what a 'vacuum consist of'. So our discussion is still very much relevant.
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Depends on how you define a vacuum. If you think of it as a 'field' containing 'energy' aka 'virtual particles' then even a 'perfect vacuum' is 'something'.
That answers a question like: under what conditions would “an absolute vacuum” be “something”. However, that was not the question.
But if we ignore that interpretation then what's not there, is not there. I'm not being partial here, it's more of a question of how you look at it
Any interpretation of nothing that makes it something is “playing fast and loose” with language. Language is the medium by which we exchange information, so I think it is very important that we should not mess it about.
"If a vacuum is defined by it being 'nothing', it can have none of these properties." Well, it does have those properties, the vacuum is also called space and space 'bends' etc. It actually needs a geometry to exist, well, as I see it then.
Then, neither space, nor the vacuum can be considered as nothing. It's as simple as that.
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The vacuum is definitely not nothing. It has energy. Space is just a name for that which we use to define distance.
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There is one important point though. Presuming a vacuum to be nothing but still giving us an appearance (observer dependent), what would make it 'exist'? In such a case, to me, the geometry of our universe becomes interesting, and with it my original question(s).
If a vacuum is defined as “nothing”, then any observer dependent attribute must be an illusion. However, if we accept that our improved understanding of the nature of the vacuum is such that we now know that it is “something”, and we re-define the term “vacuum” in accordance with that; there is no problem.
Only when we indulge in semantic contortions like insisting that nothing is something do we run into difficulties.
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Space is just a name for that which we use to define distance.
I think I'm OK with that (for the purposes of this discussion, anyway), but I would anticipate some eyebrow raising on the part of those who would argue that space (or spacetime) can be physically distorted.
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:)
Ok
You don't think observer dependencies are true then Bill?
As you write that " but I would anticipate some eyebrow raising on the part of those who would argue that space (or SpaceTime) can be physically distorted."
Or maybe it's about semantics again?
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I'm sorry if you thought of it as a 'exclusive discussion' btw. It was presenting alternatives, not trying to convince anyone. As I stated before ever writing here, this is what I do to understand it myself. I test the logic and try to see if it makes sense to me, which also means that I have several views.
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But yes, observer dependencies are correct, and true. I don't have any problems with that, it's the variant conclusions you may make from it that still holds my interest. http://www.askamathematician.com/2010/09/q-how-does-the-twin-paradox-work/
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I’ve obviously given the wrong impression – more than once!
You don't think observer dependencies are true then Bill?
As you write that " but I would anticipate some eyebrow raising on the part of those who would argue that space (or SpaceTime) can be physically distorted."
I have no problem with observer dependence, in general. My comment: “If a vacuum is defined as “nothing”, then any observer dependent attribute must be an illusion” referred specifically to anything that anyone might observe, and identify as an attribute of “nothing”.
As I see it; if it has attributes, it is not "nothing". If it is "nothing", and attributes are observed; then either "it" has to be redefined as "something", or the observed attributes are illusions.
The comment about eyebrow raising referred specifically to Jeffrey’s statement: “Space is just a name for that which we use to define distance.”
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BTW. If I gave the impression I thought this was an 'exclusive discussion', I apologise. Another wrong impression. I blame my age. :)
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Space is just a name for that which we use to define distance.
I think I'm OK with that (for the purposes of this discussion, anyway), but I would anticipate some eyebrow raising on the part of those who would argue that space (or spacetime) can be physically distorted.
Space isn't a physical object. Just as time isn't. They are both constructions of mathematics. Due to Lorentz transformations they can both have a gradient that we can show on a space-time diagram.
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Space isn't a physical object. Just as time isn't. They are both constructions of mathematics. Due to Lorentz transformations they can both have a gradient that we can show on a space-time diagram.
You will get no argument from me, there, but then, I suspect that spacetime curvature is a concept that has led to some wrong impressions, In spite of the fact that it provides a useful way of thinking about things like gravity.
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Well Jeffrey :)
Both 'space' and 'time' are properties existing, long before mathematics was 'invented',. The Chinese used yin and yang for describing it, vacuum contra matter, cold contra hot, female contra male. It's been around for a really long time.
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Although time stood by itself, they still used 'work done' as defining the distance. Going up the mountain made for a longer 'distance' than going down which, even though it makes sense, craves another way to look at it.
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BTW; Interesting link to askamathematician. At a cursory glance, I have less problems with that than I had with his answer to the question about time stopping for photons.