[Fortnum]

Hubble's observations of distant galaxies showed an increase in redshift with distance which is conventionally interpreted as an accelleration in expansion with distance. This has led to all sorts of speculation as to what might be causing such an effect. I have a problem with the statement that distant galaxies are moving away faster. Not the faster bit, but the word "are". In truth we have no idea what they are doing at this point in time, we only know that they were moving away faster when the light which left them billons of years ago started its journey to us. Our view of the universe is down a cone through time with events happening further back in time the further they are from us. So if further away from us means further back in time, Hubble's observations can be interpreted as an accelleration in expansion with distance back in time. Which in turn can be stated as a decelleration in expansion as we come forward in time. In other words the rate of expansion is slowing down, which is what might be expected.

Surely somebody must have thought of this before. Where is the error in Logic?

A corollary of the idea that accelleration varies proportionally with distance from us is that we must be at a unique point inthe universe, which is most unlikely. The idea that it changes proportionally with time would apply univerally.

[granpa]

you will get increasing redshift with distance even if the expansion isnt accelerating or decelerating.

[IM Egdall]

Hubble did not see the acceleration of the expansion of the universe. He only saw that the universe is expanding (in fact, actually it was Georges Lemaitre). But anyway, it was observations of supernovae in the late 90's which showed this expansion has been accelerating for the past 5 to 7 billion years or so.

How did the supernova data show this? Please see the article "Hubble, Keck, and Nobel Prize" in my science forum blog - Its Relative - for an explanation.

This post has been edited by IM Egdall: 6 December 2011 - 12:16 AM

[granpa]

https://forums.craig...g/?ID=201238589

[JustinW]

I also do not believe the universe is expanding or will expand infinately. I have heard dark energy used to explain the expansion, but there is the fact that something will have to produce that energy. If that energy is not being produced then it will eventually be depleated allowing the gravity from within the universe to cause contraction.

I have also thought; if the universe is expanding on such a scale, then maybe it could be caused by vacuum greater than that of space by whatever it is that surrounds the universe.

[zapatos]

JustinW, on 6 December 2011 - 08:38 PM, said:

I also do not believe the universe is expanding or will expand infinately. I have heard dark energy used to explain the expansion, but there is the fact that something will have to produce that energy. If that energy is not being produced then it will eventually be depleated allowing the gravity from within the universe to cause contraction.I have also thought; if the universe is expanding on such a scale, then maybe it could be caused by vacuum greater than that of space by whatever it is that surrounds the universe.

If the universe is expanding at a sufficient rate then no additional energy will be required to allow the universe expand indefinitely. Gravity would not be able to overcome the rate of expansion. Similar to escape velocity.

[imatfaal]

JustinW, on 6 December 2011 - 08:38 PM, said:

I also do not believe the universe is expanding or will expand infinately. I have heard dark energy used to explain the expansion, but there is the fact that something will have to produce that energy. If that energy is not being produced then it will eventually be depleated allowing the gravity from within the universe to cause contraction.

I have also thought; if the universe is expanding on such a scale, then maybe it could be caused by vacuum greater than that of space by whatever it is that surrounds the universe.

One front-runner idea is that the vacuum of space has an inherent energy; as the energy is related to the volume of space, the greater the volume the greater the energy and there is no depletion or dilution of energy by creation of new space - Dark Energy Cosmological Constant. Whilst this is just one of many hypotheses at present it does demonstrate how the "running out of energy" problem can be solve.

And note what Zapatos has mentioned - do not confuse the expansion of the universe with the acceleration of the expansion of the universe. Dark energy is the "placeholder name" for the theory that will explain the acceleration of the expansion. The expansion itself requires no additional energy input and is well understood

This post has been edited by imatfaal: 7 December 2011 - 11:30 AM

[JustinW]

After reading a little about vacuum and expansion of the universe I came across some things which I didn't quite understand and couldn't find an answer for.
If space is a vacuum and is expanding, shouldn't the vacuum of space grow proportionately to that expansion? It seems to me that if space between matter grows to cause the negative pressure in a vacuum to grow, then the universe would somehow have to cyclically feed itself to keep a somewhat steady measurement of vacuum. Even allowing room for fluctuation. This is of course assuming on my part since I couldn't find any information on the changes in measurement for the vacuum of space. Just what the measurements were, so I assumed they were somewhat constant.

Another question is, how is it possible for dark energy to have no effect on the attraction of gravity on one scale but have such a big inpact on a cosmological scale? You would think that dark energy having an effect that we can see and measure in the cosmos would also have an identical effect on a galactic level or smaller.

[zapatos]

JustinW, on 8 December 2011 - 09:24 PM, said:

Another question is, how is it possible for dark energy to have no effect on the attraction of gravity on one scale but have such a big inpact on a cosmological scale? You would think that dark energy having an effect that we can see and measure in the cosmos would also have an identical effect on a galactic level or smaller.

The effect of gravity decreases with distance.

As an analogy, imagine a bar magnet laying on your desk and a metal ball bearing stuck to the end of it. If there is a steady breeze blowing over the ball bearing it won't move because it is too close to the magnet. The further you move the ball bearing from the maget the less the impact the magnet has on the ball bearing, until at some point the breeze will become the dominant force and the ball bearing will start to roll away.

In a similar way, if galaxies are close enough to each other, dark energy cannot overcome the force of gravity. However, at a great enough distance, dark energy becomes the dominant force.

[DrRocket]

JustinW, on 8 December 2011 - 09:24 PM, said:

After reading a little about vacuum and expansion of the universe I came across some things which I didn't quite understand and couldn't find an answer for.
If space is a vacuum and is expanding, shouldn't the vacuum of space grow proportionately to that expansion? It seems to me that if space between matter grows to cause the negative pressure in a vacuum to grow, then the universe would somehow have to cyclically feed itself to keep a somewhat steady measurement of vacuum. Even allowing room for fluctuation. This is of course assuming on my part since I couldn't find any information on the changes in measurement for the vacuum of space. Just what the measurements were, so I assumed they were somewhat constant.

Another question is, how is it possible for dark energy to have no effect on the attraction of gravity on one scale but have such a big inpact on a cosmological scale? You would think that dark energy having an effect that we can see and measure in the cosmos would also have an identical effect on a galactic level or smaller.

Vacuum energy, as in quantum electrodynamics, does indeed create a "negative pressure" which should translate into a positive cosmologcal constant (aka dark energy). This has essentially nothing to do with any ordinary measurements of vacuum pressure. Unfortunately the usual calculation results in over predicting the observed acceleration of expansion by about 120 orders of magnitude. That is a colossal error. The botom line is that nobody understands this or has any physical explanation for dark matter.

Dark energy does have an effect on the galactic and smaller levels. It is just that the effect is dwarfed by gravity in regions in which matter is concentrated. The effect is miniscule. In regions of deep space where matter density is extremely tiny the effect of dark enrgy, though small locally, dominates. There s an awful lot of deep space out there.

[pantheory]

Fortnum, on 4 December 2011 - 06:34 PM, said:

Hubble's observations of distant galaxies showed an increase in redshift with distance which is conventionally interpreted as an accelleration in expansion with distance. This has led to all sorts of speculation as to what might be causing such an effect. I have a problem with the statement that distant galaxies are moving away faster. Not the faster bit, but the word "are". In truth we have no idea what they are doing at this point in time, we only know that they were moving away faster when the light which left them billons of years ago started its journey to us. Our view of the universe is down a cone through time with events happening further back in time the further they are from us. So if further away from us means further back in time, Hubble's observations can be interpreted as an accelleration in expansion with distance back in time. Which in turn can be stated as a decelleration in expansion as we come forward in time. In other words the rate of expansion is slowing down, which is what might be expected.

Surely somebody must have thought of this before. Where is the error in Logic?

A corollary of the idea that accelleration varies proportionally with distance from us is that we must be at a unique point in the universe, which is most unlikely. The idea that it changes proportionally with time would apply univerally.

Hubble saw and documented what appeared to be a correlation between the redshift of galaxies and their distances as corroborated by Luminosity Distance which is based upon the inverse square law concerning brightness, in this case of galactic light. It was implied by these observations that these galaxies might be moving away from each other and us, and that what we were seeing in terms of galactic redshifts was a Doppler shift of galactic light. The correlation seemed to be linear implying a constant expansion rate. Lemaitre, a Belgium Catholic Priest, already believed that one of the solutions to Einstein's cosmological equations was an expanding universe model which he had done the preliminary work concerning these equations. When he read Hubble's paper he completed his solution verifying an expanding universe solution and wrote a paper speculating that if the universe was expanding, it likely could be expanding from a singular beginning. He called his expanding universe model his "fireworks theory." This model never gained an active following in cosmology until after the second world war, at which time it was brought back to life by Gamow, a Russian physicist who modeled this fireworks theory on the physics of the atomic bomb. At the end of the 1940's Fred Hoyle, who had his own cosmological model and therefore was not impressed with the fireworks model, dubbed Gamow's model The Big Bang Theory.

The accelerated expansion of the universe was proposed by astronomers in the early 1990's determining that the distances to type 1 supernova could not be explained unless the universe was now and presently in an accelerated expansion phase. They were given the Nobel Prize this year for that proposal and supposed discovery. It was later asserted by using these same type 1a supernova, that up until about 6 billion years ago, that the expansion of the universe was decelerating.

The expansion of the universe is based upon the assumption that the observed redshift of galactic light is a Doppler shift rather than some other possible proposed explanations. It was later assumed that this expansion of the universe was based upon the expansion of space rather than some other possible proposed explanations for Doppler relative motion. Other than the observed galactic redshifts, there is no other evidence in general discussion or proposed that I know of, that supports the proposal that the universe is expanding other that the observed galactic redshifts.
//

This post has been edited by pantheory: 9 December 2011 - 01:14 AM

[JustinW]

Yes I believe I understand the fundamentals of the theory, but since we can measure the negative pressure of space's vacuum we should be able to tell if it is getting stronger. Which is how vacuum would work if space were expanding. Am I right or did I misunderstand how a vacuum works?

Another thing bothered me about black holes forming in the primordial soup after the big bang. It was said there were densities great enough to cause black holes which they refer to as primortial black holes. Wouldn't a primortial soup give black holes enough material to grow until almost all existing material had either fallen in or had been suspended in the event horizon.(minus that which would be ejected) And if there were a black hole that fed off of primortial soup wouldn't it be larger than anything that we know exists? If this were true it would be seen in the cosmic microwave background? If not, then either primortial soup didn't exist, black holes weren't formed in it, or there has to be another reason for the black holes not to grow and be shown through the cmb. I would love to hear some feed back on this. And if anyone knows if there were ever any studies done on changing vacuum strengths in space, I would be interested. My thoughts now after reading about the cosmological constant is that if vacuum isn't getting stronger, then it might make better scince that the universe might just be moving instead of expanding. My knowledge on these subjects is lacking due to just recently taking an interest, so please correct me when I'm painfully wrong.

[guenter]

JustinW, on 9 December 2011 - 01:44 PM, said:

Wouldn't a primortial soup give black holes enough material to grow until almost all existing material had either fallen in or had been suspended in the event horizon.(minus that which would be ejected) And if there were a black hole that fed off of primortial soup wouldn't it be larger than anything that we know exists?

The early universe expanded extremely fast. This might have limited the growth of the primordial black holes. Its just a guess.

pantheory, on 8 December 2011 - 10:49 PM, said:

Other than the observed galactic redshifts, there is no other evidence in general discussion or proposed that I know of, that supports the proposal that the universe is expanding other that the observed galactic redshifts.//

In addition to that, the redshift of the CMB photons tell us that the universe expanded by 1100 times since their emission.

[granpa]

http://en.wikipedia....ic_oscillations

Quote

In cosmology, baryon acoustic oscillations (BAO) refers to an overdensity or clustering of baryonic matter at certain length scales due to acoustic waves which propagated in the early universe.[1] In the same way that supernova experiments provide a "standard candle" for astronomical observations,[2] BAO matter clustering provides a "standard ruler" for length scale in cosmology.[1] The length of this standard ruler (~150 Mpc in today's universe[3]) can be measured by looking at the large scale structure of matter using astronomical surveys.[3] BAO measurements help cosmologists understand more about the nature of dark energy (the acceleration of the universe) by constraining cosmological parameters

Imagine an overdense region of the primordial plasma. While this overdensity gravitationally attracts matter towards it, the heat of photon-matter interactions creates a large amount of outward pressure. These counteracting forces of gravity and pressure create oscillations, analogous to sound waves created in air by pressure differences.[3]

Consider a single wave originating from this overdense region in the center of the plasma. This region contains dark matter, baryons and photons. The pressure results in a spherical sound wave of both baryons and photons moving with a speed slightly over half the speed of light[7][8] outwards from the overdensity

[JustinW]

Quote

Dark energy does have an effect on the galactic and smaller levels. It is just that the effect is dwarfed by gravity in regions in which matter is concentrated. The effect is miniscule. In regions of deep space where matter density is extremely tiny the effect of dark enrgy, though small locally, dominates. There s an awful lot of deep space out there.

So your saying that dark energy is kind of like an ion propultion. A little amount of force applied constantly can increase speed to such a rate as the current expansion? (assuming it is expansion instead of just movement)