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About LinkBacksCan the Universe Only Expand if.....
....there is no boundary?
....it's filling a void?
... there is a boundary and it's displacing the boundary of something else?
....for some other reason(s)?
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October 20th, 2012, 10:43 AM
Can the Universe Only Expand if.....
....there is no boundary?
....it's filling a void?
... there is a boundary and it's displacing the boundary of something else?
....for some other reason(s)?
Paul Davies [ the goldilocks enigma ] "The universe is not an explosion IN space and time - it is an explosion OF space and time.
Your questions imply there was something there in the first place
Present theory asserts that there is no boundary to the universe. It therefore could expand if the universe were totally flat and could expand indefinitely outward, or if it curved around upon itself as considered by various other possibilities of General Relativity, but still could expand in its overall volume.Originally Posted by zinjanthropos
The universe could certainly expand if it's filling a pre-existing void of space, but it also could expand if space itself were expanding, which presently is the consensus Big Bang view.....it's filling a void?
This is an expansion possibility but probably not one considered by a normal Big Bang premise.... there is a boundary and it's displacing the boundary of something else?
The universe would necessarily be expanding if the redshift of galactic light means that space is expanding. If there is another explanation for these observed galactic redshifts then the universe may not be expanding at all which probably would require a different cosmological model.....for some other reason(s)?
Last edited by forrest noble; October 26th, 2012 at 11:47 AM.
I agree,Maybe we only see red shift because of our perspective here on Earth in the middle of a galaxy of accumulated matter. From here everything we look out at is through space that is far less dense than here. If we could view theuniverse from a remote place like between galaxies where space is the least dense would everything be blue shifted? It always gets confusing when discussing time dilations but wouldn't it make a difference if your perspective was looking from a massive object like Earth where time moves slower out into deep space where time is moving faster. Everything we see has to come through those slowing time dilations.
I agree,Maybe we only see red shift because of our perspective here on Earth in the middle of a galaxy of accumulated matter. From here everything we look out at is through space that is far less dense than here. If we could view the universe from a remote place like between galaxies where space is the least dense would everything be blue shifted?
Hey bill. It's a particular kind of redshifting we see. Not the kind we see looking at the sunset while looking through the atmosphere.
When we divide galactic light with a prism we see the rainbow type spectrum. Within the spectra we also see absorption and emission lines, thin lines that help us determine the elements within the stars that are producing the galactic light. Hydrogen is the most abundant element in galactic spectra and usually the easiest to find in galactic spectra. We usually look for a certain pattern of absorption lines which represent the different energy levels of electrons within the hydrogen atom. For most galaxies in out local group, we see small redshifting and blue shifting of galaxies within this group which would seem to be an indication of their orbital velocity around their mutual center of mass relative to our perspective. But for galaxies farther away we mostly find redshifted absorption lines which we consider means that they are moving away from us. This is similar to a Doppler shift and is thought to indicate that space itself is expanding. If we were looking through much dust the spectrum of the light would break down differently and the elements within the dust would produce their own absorption lines so we probably could make a pretty good determination that we are looking through dust.
It always gets confusing when discussing time dilations but wouldn't it make a difference if your perspective was looking from a massive object like Earth where time moves slower out into deep space where time is moving faster. Everything we see has to come through those slowing time dilations.
Yes this is true. Time dilations produced by the Earth, although readily detectable with the proper instrumentation, is relatively tiny. On the other hand when galactic light is redshifted its wavelengths are longer and the time dilation (slowing of time) is greater and can be estimated via a normal clock taking maybe 20% longer for the duration of a supernovae event at a distance of roughly 6 billion light years, for instance. Was time really running slower in that distant supernova time frame (rhetorical)? According to present theory it is just our perception of time at that distance which causes the dilation
Last edited by forrest noble; November 3rd, 2012 at 05:14 PM.
Yes, sorry I wasn't clear enough. I always assumed we were talking red shift caused by motion and nothing to do with atmosphere, dust, gas or anything that could change the actual color of light.
So what do you think would happen if photons traveling from one galaxy to another went through regions of space that have different time dilations. If time is slower within the galaxies especially at the stars then what would happen as the photons traveled outward into the areas of space between galaxies where time moves a little faster? And then more important what would happen to those same photons then as they begin to travel inward towards a galaxy (our galaxy) where time moves slower again. As we watched those photons coming at us COULD they only appear to be redshifted as they traveled through space with time dilations that were constantly slowing as the photons traveled toward the galaxy and into it?Yes this is true. Time dilations produced by the Earth, although readily detectable with the proper instrumentation, is relatively tiny. On the other hand when galactic light is redshifted its wavelengths are longer and the time dilation (slowing of time) is greater and can be estimated via a normal clock taking maybe 20% longer for the duration of a supernovae event at a distance of roughly 6 billion light years, for instance. Was time really running slower in that distant supernova time frame (rhetorical)? According to present theory it is just our perception of time at that distance which causes the dilation
When photons pass through gravitational influence, they are blueshifted on the way in, and redshifted on the way out, by the same amount.
Time dilation is correlated with galactic redshifts so that maybe minor redshifting might happen according to such a process, but according to the standard model such increases in redshift as a result would either not occur, or be miniscule.Yes, sorry I wasn't clear enough. I always assumed we were talking red shift caused by motion and nothing to do with atmosphere, dust, gas or anything that could change the actual color of light.
So what do you think would happen if photons traveling from one galaxy to another went through regions of space that have different time dilations. If time is slower within the galaxies especially at the stars then what would happen as the photons traveled outward into the areas of space between galaxies where time moves a little faster? And then more important what would happen to those same photons then as they begin to travel inward towards a galaxy (our galaxy) where time moves slower again. As we watched those photons coming at us COULD they only appear to be redshifted as they traveled through space with time dilations that were constantly slowing as the photons traveled toward the galaxy and into it?Yes this is true. Time dilations produced by the Earth, although readily detectable with the proper instrumentation, is relatively tiny. On the other hand when galactic light is redshifted its wavelengths are longer and the time dilation (slowing of time) is greater and can be estimated via a normal clock taking maybe 20% longer for the duration of a supernovae event at a distance of roughly 6 billion light years, for instance. Was time really running slower in that distant supernova time frame (rhetorical)? According to present theory it is just our perception of time at that distance which causes the dilation
But if there were another explanation for generally all of observed galactic redshifts other than space expanding, and if the observable universe is generally not expanding, then the entire foundation of Big Bang cosmology would seemingly crumble into oblivion.
The expansion of the universe is - at least so far as I understand the maths behind it - quite independent of the particular geometry and topology. Space-time can expand regardless of whether there is a boundary or not. Also, no "void to be filled" is needed for it to take place.
I think it is quite possible that the expansion of the universe can be in some models explained by the spacetime topology. For instance I think that any theory that predicts a slowing down of the rate of time, relative to the past, will produce a stretching of space. This article seems to suggest that dark energy does not exist and that we are looking at it all backwards due to time slowing down.The expansion of the universe is - at least so far as I understand the maths behind it - quite independent of the particular geometry and topology. Space-time can expand regardless of whether there is a boundary or not. Also, no "void to be filled" is needed for it to take place.
Spanish scientists say time is running out
This is another take on a slowing of time due to fractal cantorian space time geometry by the much maligned professor M.S.El Naschie.
http://msel-naschie.com/pdf/5.TimeSy...ingDuality.pdf
I think that last one is very interesting but I cannot say that I am a proponent of either. I do however have my own “pet” theory where time is transfinite but I think it best to move to the appropriate section if you would like to further discus.
I agree that “Space-time can expand regardless of whether there is a boundary or not. Also, no "void to be filled" is needed for it to take place.” As I believe that the universe is infinite, and there is always room at that hotel.
These are interesting models, I must admit. I haven't had time yet to study these in detail, so I can't really comment on it at the moment; this has awoken my curiosity though !
I have always thought expansion could be explained through timedilations of some sort. I have tried to find a way to articulate what I wasthinking but could never do it properly. In short I think it could be acombination of (1) the universes average speed of time is slowing down as theuniverse slowly condenses into matter. In other words it could be contractingright now instead of expanding. (2) As I was trying to explain in posts # 4 and6 there could be an additional effect on our perspective as we look out intospace from our local area of slower time. The combination of a shrinkinguniverse, a slowing of time and our perspective view should at least make usthink there could be other possibilities for the cause of redshift.
Minkowski once said “henceforth space by itself, and time by itself, are doomed to fade away into mere shadows and only a kind of union of the two will preserve an independent reality”. And this I think can be even truer of some fractal topologies. The speed of light is always the same no matter what your frame of reference. In the past then, if time was running relatively faster light could travel further by comparison to the present. All light that we observe is from the past so past distances are longer than the distances of the present. If time and distance is a consequence of frame dependant matter then thinking that future distances are relatively shorter than those of the present matter will be relatively smaller in the future and we can consider it is relatively shrinking along with our measuring rods and clocks.
This is what I was trying to describe. Couldn't this be the cause if not the main cause of red shift. And if there is no accelerated expaintion of the universe by association to this red shift then lets move on to something new or go back to some of the older ideas for gravity and cosmology. How can the speed of light be constant if time is not?In addition to that I have always questioned the speed of light anologies and the Michelson and Morley experiment and the fact that the whole premis of the experiment was never questioned. Relativity makes the claim that light always travels at the same speed but the speeds of everything else are dependent on the combination of adding or subtracting different speeds or accelerations. If I designed a model airplane that can only fly 40 MPH maximum speed because of air resistance and I launch it at 50 MPH it will still only fly at 40 MPH. If I launch it from the top of a train that is moving 60MPH the plane will still only travel 40MPH and not 100MPH. If I launch the plane in the opposite direction it will travel at 40MPH and not 20MPH. If time dilations are excepted then why isn't resistance to photons?
Hold your horses here, bill alsept. The concepts referenced in post 10 are very interesting, and certainly are worth further consideration. However, they would require very careful analysis first, and a non-constant speed of light through the history of the universe would have far-reaching and non-trivial consequences above and beyond red-shift observations. A trivial example would be that the fine-structure constant would have had a different value, which has consequences for nuclear decay rates and the stability of certain elements. I am not aware of any strong evidence in support of this, in fact most empirical data we have seems to indicate that that constant is in fact just that - constant. See here :
Natural nuclear fission reactor - Wikipedia, the free encyclopedia
All I am saying here is - it's an interesting hypothesis, but not to be confused with scientific fact.
The idea of a changing rate of time and/or matter contracting rather than space expanding came up on another forum recently. These are valid alternative views of big bang cosmology. You just choose a different set of coordinates. The ones we currently use (speed of light constant, space expanding, etc.) seems most natural to most people and is easiest to work with.
This is what I wrote on the other forum, which I think is relevant here:
Another poster, who knows much more than me (he may teach this stuff) added:
Which gives me another opportunity to plug: Introduction - 10,000 Year Clock - The Long Nowlet me just add that the reason we choose to use our conventional coordinates is because they are natural for observers moving with the hubble flow. The coordinate time on the clock following that path will tick proper time. We could for example put the big bang in the infinite past usingbut then this coordinate time will not correspond to the time an actual clock ticks that moves with the hubble flow. So the big bang really was 13.7 billion years ago in the physical sense that an inertial clock that has existed all that time will now unequivocally read 13.7 billion years. Unless its batteries ran out in that time of course.
As for your point 2, it is not clear what could affect things from "our perspective". Apart from being in the gravity well of our galaxy but this is too small and would cause a constant effect for all distant galaxies.
Yes Marcus we should approach these ideas with caution. Bill I think has made some incorrect assumptions there. As I said in post 13 “The speed of light always remains the same no matter what your frame of reference”. We can however regard light as having a peculiar velocity outside our frame of reference. For instance a flash of light from s supernova in our galaxy will in the future, let’s say in 1000 million years’ time, will have a peculiar velocity faster than the speed of light relative to the source due to space expanding over that amount of time. Conversely light from a very distant galaxy that we receive with a redshift will have travelled at a velocity peculiar to us that was slower than the speed of light. We can use the analogy of a conveyor like those at airports, as light leaves the distant galaxy it is travelling towards a destination that is moving away, this is like running the wrong way on the conveyor, the conveyor is the frame of reference and so the constant speed is correct to that but peculiarly slower relative to the destination. The closer it gets to the destination the slower the conveyor goes and stops as the light reaches us at the speed of light. This idea is excepted and well known I think, where I want to take this next may not be. I think therefore I should start a new thread in “new ideas and hypothesis”.Hold your horses here, bill alsept. The concepts referenced in post 10 are very interesting, and certainly are worth further consideration. However, they would require very careful analysis first, and a non-constant speed of light through the history of the universe would have far-reaching and non-trivial consequences above and beyond red-shift observations. A trivial example would be that the fine-structure constant would have had a different value, which has consequences for nuclear decay rates and the stability of certain elements. I am not aware of any strong evidence in support of this, in fact most empirical data we have seems to indicate that that constant is in fact just that - constant. See here :
Natural nuclear fission reactor - Wikipedia, the free encyclopedia
All I am saying here is - it's an interesting hypothesis, but not to be confused with scientific fact.
Yes, that idea is fully accepted. Light propagates relative to the Hubble flow.
For the first 4.5 billion years of the history of the universe, for instance, the photons that make up the Cosmic Microwave Background Radiation that we currently detect were actually being taken away from here by the Hubble flow. The CMBR we currently detect was originally released only around 40 million light-years away, but at that time the rate of expansion was so fast that the radial distance to those photons was increasing at more than 50 times the speed of light!
It took 4.5 billion years for those photons to reach the edge of our Hubble sphere (where the recession speed is only c), due primarily to the deceleration of the rate of expansion, by which time they were 5.8 billion light-years away! Only then did they start to make actual progress towards us, from our frame of reference.
But that is simply a description of the cosmological variety of the coordinate speed of light, which should not be confused with the proper speed of light which is always c. We know the proper speed of light is intrinsically linked to the fine-structure constant, and we have evidence that the fine-structure constant has not changed over the past few billion years at least.
No, it will be red-shifted, but its speed will remain the same.
It seems we agree that the speed of light and the way we perceive it can be effected by other factors. It seems to me that this perception can be effected by not only this conveyer belt effect and shift the light red or blue depending on direction but were we not also talking about the other reason that the speed of light could appear to change? Time dilations and their effects from different or changing perspectives. Could we put math to this and I'm sure someone has and assign a value for time at each and every point in the universe. And just for sake of conversation our local time (A) is given the value of (1) This assigned value we would most likely find to be common throughout the universe at areas where the local mass and conditions where similar to Earths. Also for the sake of conversation we give time a value of (10) at the most remote areas of the universe (B) like the areas in the middle of the voids of the large structures. The time values would be different at all points along the way from point A to B. From our point of view here on Earth in the gravity well of the Milky Way what would a formula for A, B and C look like for light leaving a distant galaxy (C) from a point similar to Earths so we will assign it a value of (1) and then being viewed from (A) after traveling a certain distance through point (B) and all the other time varying point? This formula of course would also be affected by the overall motion if any of the area between A and C. For simplisity assume it to be flat. Look forward to your post in
Not sure how you mean this; there is no absolute time you could assign to a point, you can only compare clocks between events. You can assign a value for proper time of a clock travelling from point A to B, like so :
I'm just saying Time would have a value or a factor applied to it at different locations depending on its relation to local mass. In other words like I said if we assign time a factor of (1) here on Earth and outside of our solar sytem maybe a factor of (1.5), the void areas between the arms of a spiral galaxy maybe a (3.2), outside and between galaxies a (7) and at the middel of the voids of the large structures a (10).
Not sure how you mean this; there is no absolute time you could assign to a point, you can only compare clocks between events. You can assign a value for proper time of a clock travelling from point A to B, like so :
You could do it as clock readings relative to one another, since clocks in a stronger gravitational field are dilated as compared to clocks resting sufficiently far away. So yes, it can be done.
I haven't done the math (as if!) but I am fairly sure that your "10" would be a fraction of a percent.
bill alsept,
Yeah, Bill, as Strange suggested there is very little time dilation in such large voids. Cosmological redshift time dilation is directly proportional to the observed redshift whereas the change in time increases according to the observed redshift 'z.' For instance a redshift of 'z' would produce a time dilation of (z+1)/ 1 times T (time elapsed). According to the standard model this is not a real change in time either, just an increase in the observed time lapsed due to the expansion of space. So such time dilation due to the distant location and related redshift surrounding such of a large void, would not be real.I'm just saying Time would have a value or a factor applied to it at different locations depending on its relation to local mass. In other words like I said if we assign time a factor of (1) here on Earth and outside of our solar system maybe a factor of (1.5), the void areas between the arms of a spiral galaxy maybe a (3.2), outside and between galaxies a (7) and at the middle of the voids of the large structures a (10).
On the other hand, when the real motion of a particle approaches the speed of light, for instance, its decay rate, and therefore its time dilation (slowing of time) would be real. This is what the twin paradox in Special Relativity addresses: time dilation based upon velocity. Gravitational time dilation is also normally very small excepting for great gravitational influences such as volumes surrounding black holes. In large voids there would be the opposite condition. Time would run at a very slightly faster rate than here on Earth because there would be maybe no cause of real time dilation; time would run as fast as it possibly could.
Last edited by forrest noble; November 5th, 2012 at 12:06 PM.
This is what is known as gravitational time-dilation, which Markus and Strange alluded to above. And as Strange was thinking, the time-dilation between the Earth and the middle of the voids between the large scale structures is very small indeed - but cosmologists do already take this into account. The age of the universe, for instance, is not given relative to time on Earth, but what is known as cosmological time, which "runs a little faster" than time on Earth.I'm just saying Time would have a value or a factor applied to it at different locations depending on its relation to local mass. In other words like I said if we assign time a factor of (1) here on Earth and outside of our solar sytem maybe a factor of (1.5), the void areas between the arms of a spiral galaxy maybe a (3.2), outside and between galaxies a (7) and at the middel of the voids of the large structures a (10).
Not sure how you mean this; there is no absolute time you could assign to a point, you can only compare clocks between events. You can assign a value for proper time of a clock travelling from point A to B, like so :
(Still.. can't.. resist!)
I realize that the differences between the speed of time here on Earth and at the most remote places may be small. I also realize that time would go much slower in the area of a large mass or maybe on a much smaller area like inside an atom. These areas would be given factors less than (1). I don't know how or if they calculated this when deciding that redshift could only be caused by expansion of the universe. Also if there is a math to perform these equations then I am more interested in the answers than the formula considering I wouldn't understand it anyway,,, yet. So... What would be our perceived affect (redshifted, blueshifted or no affect) of photons that had traveled from point C to A through all of those time dilations?This is what is known as gravitational time-dilation, which Markus and Strange alluded to above. And as Strange was thinking, the time-dilation between the Earth and the middle of the voids between the large scale structures is very small indeed - but cosmologists do already take this into account. The age of the universe, for instance, is not given relative to time on Earth, but what is known as cosmological time, which "runs a little faster" than time on Earth.(Still.. can't.. resist!)I'm just saying Time would have a value or a factor applied to it at different locations depending on its relation to local mass. In other words like I said if we assign time a factor of (1) here on Earth and outside of our solar sytem maybe a factor of (1.5), the void areas between the arms of a spiral galaxy maybe a (3.2), outside and between galaxies a (7) and at the middel of the voids of the large structures a (10).Not sure how you mean this; there is no absolute time you could assign to a point, you can only compare clocks between events. You can assign a value for proper time of a clock travelling from point A to B, like so :
Gravitational time dilation is only between the source and the detector. If the source had more gravity than around here, we see gravitational redshift. If the source had less gravity, we see a gravitational blueshift.
Nothing the light passes in between source and detector makes any difference to the spectrum. The light is blueshifted on the way into the gravity field of an object by the same amount as it is redshifted on the way out. Only the difference between source and detector shows up.
Light in any frame of reference will always remain the same but light travelling through one frame can be perceived to be travelling from the perspective of another frame at a peculiar velocity this does not violate relativity. This interesting document explains it well:No, it will be red-shifted, but its speed will remain the same.
http://arxiv.org/pdf/astro-ph/0310808v2.pdf
I don't think peculiar velocity is the correct term to use there, hence the confusion. Light always travels at a proper speed of c.
Coordinate speed might be a better term to describe how light on our past light cone first moves away from us before coming back towards us as shown by the teardrop shape on the spacetime diagram for proper distance on page 3 of that very famous paper. You will find that my description in post #18 matches the findings in that paper (it is easier to see this using the diagrams on page 11).
I know that paper very well indeed and so does Markus. I think he misunderstood you, due to the usage of peculiar velocity.
Last edited by SpeedFreek; November 2nd, 2012 at 07:22 PM.
"On the way out" could be anywhere from the center of the mass (C) all the way out to between the galaxies so how can you say nothing in between has an effect?. And same goes for "on the way into the gravity field" At what point do you call your points of source or detector? At the center of a star, the surface, the edge of its solar system or the edge of its galaxy. Besides if the photon is not effected by any time dilations along its path then what causes the gravitational shift? I think the different time dilations that the light passes through has to make a difference. Even your statement "on the way into the gravity field" insinuates changes along the way. That brings up another interesting question, when a photon from a distant star hits my eye and that point of detection is the only point effecting it how am I seeing the changes as you say on the way into the gravity field?
Because it is symmetrical. It goes in and comes out again. If light passes though a galaxy, past a star or whatever it will be temporarily blue shifted as it goes into the gravitational potential. As it carries on, it emerges out of the same potential and gets equally red shifted. There can be no net change.
A bit like throwing a ball up in the air. It will gradually slow down, exchanging kinetic for potential energy. It will then fall down again accelerating to exactly the same speed at which you threw it.
The only thing that is not symmetrical is the difference between the source and us.
We are talking about gravitational redshift on a cosmological scale here, and relating it to the universe as a whole. When we look at a distant galaxy, the light from that galaxy has to "climb out" of the gravitational well of that galaxy, and is redshifted as it does so. If it passes another galaxy on its way to us, it will be blueshifted as it falls down the gravitational well and redshifted as it climbs out again, by the same amount. So it will still carry the redshift of the originating galaxy, but nothing else. When it reaches us, we are sitting in the gravitational well of the Milky-Way, so the light will be blueshifted by a certain amount as it reaches us. If the curvature of spacetime (gravity) around the original galaxy is larger than the curvature around the Milky-Way, it will show a net redshift as it reaches us as the light has climbed more than it has fallen, or if the curvature around the Milky-Way is larger, it will show a net blueshift as it has fallen more than it has climbed."On the way out" could be anywhere from the center of the mass (C) all the way out to between the galaxies so how can you say nothing in between has an effect?.
Source = emission distance from centre of mass. Detector = detection distance from centre of mass. Both these distances determine the difference in gravitational potential between the two frames involved.
You could look at the very good wiki article about gravitational redshift to see how this works in practice.
Thank you informing me of another way to express this, the use of the wrong terminology can often be the cause of an amateur like myself to be misinterpreted. However the term coordinate speed is not used in that particular document whereas the term peculiar velocity is used half a dozen times.I don't think peculiar velocity is the correct term to use there, hence the confusion. Light always travels at a proper speed of c.
Coordinate speed might be a better term to describe how light on our past light cone first moves away from us before coming back towards us as shown by the teardrop shape on the spacetime diagram for proper distance on page 3 of that very famous paper. You will find that my description in post #18 matches the findings in that paper (it is easier to see this using the diagrams on page 11).
I know that paper very well indeed and so does Markus. I think he misunderstood you, due to the usage of peculiar velocity.
In ɅCDM cosmology it is the cosmological constant (Ʌ) that creates the peculiar velocity of light calculated over the commoving distances between emitter and observer, but in a model where time is slowing down over time the universe will have always been expanding and ever faster and this expansion is relative to the frame of reference of an observer, there is no need for the ad hoc Ʌ to describe what is observed. The speed of light is not changing what I think should be considered is that the relative distances are changing.
But the term peculiar velocity is never used to describe the speed of light across a comoving distance, only locally. The peculiar velocity of light is always c. Nothing can have a peculiar velocity faster than c, which is why Markus was questioning your original statement.
All the instances of that term from the paper:
Light that superluminally receding objects emit propagates towards us with a local peculiar velocity of c, but since the recession velocity at that distance is greater than c, the total velocity of the light is away from us.Galaxies that are receding from us superluminally are at rest locally (their peculiar velocity, vpec = 0) and motion in their local inertial frames remains well described by special relativityIn addition, objects that have a peculiar velocity also move through comoving coordinatesThe peculiar velocity of light is always c so the total velocity of light whose peculiar velocity is towards us is vtot = vrec − c which is always positive (away from us) when vrec > c.The point Davis and Lineweaver are making here is that a photon always has a peculiar velocity of c (peculiar velocity means velocity relative to its locale), but when using comoving coordinates it can have a "total" velocity greater than c.This expression confirms our previous statement that the peculiar velocity of a photon, Rχ˙, is c.
An appropriate term for that "total" is coordinate velocity, or even apparent velocity, but not peculiar velocity, which has a very specific meaning.
Not peculiar velocity!
And it is not Lambda (Ʌ) that is the cause of expansion. It is Lambda that is fuelling the acceleration of the expansion. The model still had apparent recession speeds faster than light before we discovered the expansion was accelerating.
The universe has not been "always expanding and ever faster". What I mean is it has not always had accelerating expansion. For the first 7-8 billion years the rate of expansion was decelerating, and only around 6 billion years ago did the deceleration turn into an acceleration.
Or less than c
Thank you SpeedFreak this is the sort of advice I need and appreciate. I will alter my use of the term accordingly.The point Davis and Lineweaver are making here is that a photon always has a peculiar velocity of c (peculiar velocity means velocity relative to its locale), but when using comoving coordinates it can have a "total" velocity greater than c.
An appropriate term for that "total" is coordinate velocity, or even apparent velocity, but not peculiar velocity, which has a very specific meaning.
You are of course right that any expansion of an infinite universe will cause an apparent super-luminal recession. A constant expansion would put the interface between luminal and super-luminal recession at the particle horizon. Any increase in the expansion rate such as the early inflation and what now appears to have been happening over the past 6 billion years will move that interface away from the particle horizon towards the observer.And it is not Lambda (Ʌ) that is the cause of expansion. It is Lambda that is fuelling the acceleration of the expansion. The model still had apparent recession speeds faster than light before we discovered the expansion was accelerating.
I think that maybe that it is in trying to fit observations to the standard model that we assume this very fast expansion then the slowing down followed by the speeding up again scenario. I am in no position to say that this is wrong but it does seem very unlikely to me.The universe has not been "always expanding and ever faster". What I mean is it has not always had accelerating expansion. For the first 7-8 billion years the rate of expansion was decelerating, and only around 6 billion years ago did the deceleration turn into an acceleration.
When I said the universe was always expanding and ever faster it was as a consequence of time slowing down over time and as such a different type of cosmological model than the standard model.
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