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Expansion of the universe

by C. Bernard
Tags: expansion, universe
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John15
#19
Apr2-12, 10:10 AM
P: 94
I have the same problem with redshift. I have seen the graphs and yes speed over distance shows acceleration but change distance for time and you get a deceleration i.e. redshift in light say 10 million years old is much less than that for 10 billion year old light. so the question is should we be using distace or time?
space_buster
#20
Apr2-12, 10:28 AM
P: 13
Charts of supernova as a function of red shifts are used to determine the speed of expansion of universe. Adam Riess first looked at the results, he was quite surprised–the expansion of the universe was not decelerating, but accelerating–it was expanding faster and faster! The most likely explanation was that old cosmological constant term of Einstein!
Drakkith
#21
Apr2-12, 04:19 PM
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Quote Quote by John15 View Post
I have the same problem with redshift. I have seen the graphs and yes speed over distance shows acceleration but change distance for time and you get a deceleration i.e. redshift in light say 10 million years old is much less than that for 10 billion year old light. so the question is should we be using distace or time?
I don't see how your are getting a deceleration. In either time or distance the redshift has been increasing.
John15
#22
Apr3-12, 07:55 AM
P: 94
The highest redshift is the CMB at 13.5 billion years, andromeda at 2.5 million years is blueshifted, the further back in time you go the higher the redshift therefore the closer in time the lower the redshift.
Drakkith
#23
Apr3-12, 03:50 PM
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Quote Quote by John15 View Post
The highest redshift is the CMB at 13.5 billion years, andromeda at 2.5 million years is blueshifted, the further back in time you go the higher the redshift therefore the closer in time the lower the redshift.
Of course, the closer the galaxy is the less time the light has been in transit to us and the less the force of expansion is on it, resulting in a slower recession velocity. Andromeda is so close that expansion has pretty much zero effect on it and the gravitational force between our galaxies are drawing us closer to gether, resulting in the blueshift we see. Using either distance or time is perfectly acceptable as long as you are consistant and clear about it. Something that is 11 billion years back in time, meaning the light has been travelling for 11 billion years to reach us is NOT 11 billion light years away, it is much further thanks to expansion.

Lets be clear by what we mean by acceleration. The expansion rate has been observed to be increasing over time, meaning that the recession velocity at a particular distance is greater now than it used to be. This is what we mean by "the expansion is accelerating". The redshift itself has always been increasing the further away an object is due to expansion.
John15
#24
Apr9-12, 09:24 AM
P: 94
Further clarification would be appreciated.
Granted the object from which light has been travelling from for the 11 billion years is now further away but how do we know it still exists. Also how do you know at what point in that 11 billion years the light was redshifted?
The expansion rate has been observed to be increasing over time, by this am I correct in assuming that a certain galaxy has been watched over say the last 100 years and the redshift is now greater than it was then as this is obviously the only way to be certain that redshift is increasing, comparing 5 and 10 billion year old light cannot in any way be accurate.
Drakkith
#25
Apr10-12, 12:20 PM
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Quote Quote by John15 View Post
Further clarification would be appreciated.
Granted the object from which light has been travelling from for the 11 billion years is now further away but how do we know it still exists.
It doesn't exist NOW as we see it, as it has had 11 billion years to change. It may have merged with another galaxy or something, but the matter that makes it up definately still exists. Matter, mass, and energy do not simply disappear for no reason.

Also how do you know at what point in that 11 billion years the light was redshifted?
The light has been redshifted over the entirety of its journey by the expansion of space. There is no single event that caused the redshift.

The expansion rate has been observed to be increasing over time, by this am I correct in assuming that a certain galaxy has been watched over say the last 100 years and the redshift is now greater than it was then as this is obviously the only way to be certain that redshift is increasing, comparing 5 and 10 billion year old light cannot in any way be accurate.
No, we look at the recession velocity of galaxies at many different distances from us, since doing so allows us to look at many different points in the past and observe how the universe was back then. I think a single galaxy has such a small increase in recession velocity over 100 years that it is not capable of being measured. Even if we can, we have not been able to measure redshift of galaxies accurately enough for more than a few decades if that. I believe it has only been within the last decade or so that we have been able to measure the velocity of nearby stars to within a few meters per second relative to us.
GeorgeDishman
#26
Apr10-12, 05:40 PM
P: 255
Quote Quote by John15 View Post
Further clarification would be appreciated.

The expansion rate has been observed to be increasing over time, by this am I correct in assuming that a certain galaxy has been watched over say the last 100 years and the redshift is now greater than it was then as this is obviously the only way to be certain that redshift is increasing, comparing 5 and 10 billion year old light cannot in any way be accurate.
Actually, measuring the wavelength of spectral lines is one of the most accurate measurements possible in astronomy. The ratio of the wavelength received to that transmitted is the "redshift".

The following are 'toy' figures intended to illustrate the method and aren't particularly accurate. Suppose we look at three galaxies which are at distances of 100, 200 and 300 million light years and the light from them has been redshifted by 1.1%, 2.1% and 3.0% respectively. We can deduce that the light was "stretched" by 1.1% in the last 100 million years, by 1.0% from 200 to 100 million years ago and by 0.9% in the preceding 100 million years (from 300 to 200). From those we can say that the rate of expansion is increasing by 0.1% per 100 million years.

Does that help explain how a set of specific redshifts can be used to determine not only the current rate but also the history of the rate? In reality of course we have thousands of results each adding a point to the graph as well as a theoretical curve which fits very well.
Naty1
#27
Apr13-12, 02:10 PM
P: 5,632
You guys agonizing about acceleration might take a look here at the 'deceleration
parameter' , q, ....and note the accompanying diagram:

http://en.wikipedia.org/wiki/Hubble_...f_the_universe

In a link:
... observations of distant type Ia supernovae indicate that q is negative; the expansion of the universe is accelerating.
Type Ia are a 'standard candle' ....a fixed brightness from which we can calibrate things...becuase the fixed brilliance is related to distance....roughly like car headlights from the same model car at varying distances.....
SHISHKABOB
#28
Apr13-12, 02:14 PM
P: 614
Quote Quote by John15 View Post
The highest redshift is the CMB at 13.5 billion years, andromeda at 2.5 million years is blueshifted, the further back in time you go the higher the redshift therefore the closer in time the lower the redshift.
just so you know, Andromeda is blueshifted because it is moving towards us due to the gravitational forces between the Milky Way and Andromeda. At small distances, things like gravity are much more influential than the expansion of the Universe.

It's like what if the Moon had a charge of +1C and the Earth had a charge of +1C too. There'd be a repulsive force between the Earth and the Moon due to electrostatic forces, but the force due to Gravity is much stronger and so has much more influence.
John15
#29
Apr17-12, 06:08 AM
P: 94
George the first explaination I have seen along those lines, I can see how the accumulation can work, it still assumes though that space is expanding i.e. if light was redshifted as it left the 300 million light year galaxy with the full 3% redshift because it was moving faster then then the redshift from the closer galaxies would be smaller if there had been a deceleration in that time with no expansion of space. Your explaination seems to rely on the expansion of space rather than the movement of the galaxies. Is redshift caused by the expansion of space or the movement of the galaxies?
Also redshift must be relative to the moving bodies i.e. take 3 bodies moving in the same direction along the same axis 1 moving at 100 2 (middle) moving at 70 3 moving at 40. These are all moving apart in the same direction and I think I am correct in saying the redshift from 2 - 3 and 2-1 would be the same.
I am not disputing redshift just questioning if the interpretation is correct and all other possible causes have been checked and ruled out, possibly because I cannot see how space can just materialize out of nowhere unless it worked out like our tectonic plates, maybe the great attractor is an area of dissapearing space.
Regarding andromeda, the BB theory relies at least in part on the fact that galaxies seem to be moving apart so they must have been closer together in the past, of course if andromeda is moving towards us now then by the same reasoning it must have been further away in the past which is a bit contradictory.
bapowell
#30
Apr17-12, 11:15 AM
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Quote Quote by John15 View Post
andromeda is moving towards us now then by the same reasoning it must have been further away in the past which is a bit contradictory.
The big bang theory is consistent with a uniform and isotropic expansion of the universe on sufficiently large scales where the energy density itself is close to uniform and isotropic. However, not all galaxies are at rest with respect to this expansion (simply being carried along with it), nor should they necessarily be. Interactions with other galaxies, as well as small perturbations during galaxy formation, can lead to non-negligible galactic velocities relative to the expansion (called peculiar velocities.) So, in fact, Andromeda's motion towards our galaxy is perfectly consistent with a full consideration of gravitational dynamics that includes the effects of local structure. As shishkabob says above: the local interaction dominates the tendency for Andromeda to move along with the expansion of the universe. It is not even a bit contradictory.
GeorgeDishman
#31
Apr17-12, 01:17 PM
P: 255
Quote Quote by John15 View Post
George the first explaination I have seen along those lines,..
I'm glad I could put in new terms, sometimes a different way of looking at a question makes the answer more understandable. You should understand I'm not offering anything original, just explaining the standard model in a different style.

Regarding andromeda, the BB theory relies at least in part on the fact that galaxies seem to be moving apart so they must have been closer together in the past, of course if andromeda is moving towards us now then by the same reasoning it must have been further away in the past which is a bit contradictory.
This relates to your other questions so I'll address it first. The effect of cosmological expansion is proportional to the distance between objects so for example within the Solar System the effect is virtually undetectable and if you dropped a brick, you would be very surprised if it fell upwards because the gap between it and the Earth "expanded".

This map shows our Milky Way, Andromeda and other smaller members of our local group. All these are so close together they behave like the planets in the Solar System (though not in a neat plane).

http://www.atlasoftheuniverse.com/localgr.html

Now click the "Zoom out x20" button. We are in the middle. To the right is the Virgo Cluster which has over 200 large galaxies. They too are gravitationally bound, they are too close for expansion to overcome their mutual gravity.

The same is true of the Fornax and Eridanus clusters (lower left) but they are so far from the Virgo Cluster that (to the best of my knowledge) the two sides will always be moving apart, the expansion is the greater effect at that separation.

Within bound groups, the motion within the cluster determines the spectral shift through the old fashioned Doppler Effect, with which I am sure you are familiar, which is why Andromeda has a blue shift.

I can see how the accumulation can work, it still assumes though that space is expanding i.e. if light was redshifted as it left the 300 million light year galaxy with the full 3% redshift ...
Take a sheet of paper and draw two dots close together at the bottom. That the distant galaxy and ours 300 million years ago. Now draw two dots at the top of the sheet farther apart for it and us now. Draw a line join the old and new location for the distant galaxy and another for ours something like this:

\ /

The angle between the lines is the relative velocity. If the angle is 1 degree, it doesn't make any sense to say that it occurs either "at" the left line or the right line. Redshift is a function of the angle between the lines.

... Your explaination seems to rely on the expansion of space rather than the movement of the galaxies. Is redshift caused by the expansion of space or the movement of the galaxies?
Both. If you think of a clusters far from us, the average for the group will be the cosmological shift but each individual galaxy will have a slightly different value due to it's motion within the group, that is called "proper motion". The latter is very useful since there is a well known relation between the average velocity within the group and the total mass of the cluster.

For cosmological redshift, the effect is equal to the change in distance between the galaxies. It is as if whatever stretched the space between us also stretched the wavelength of the light. We are forced to use the two different effects because the models say that galaxies for which the effect doubles the wavelength or more, the source was moving away at more than the speed of light. Trying to use Doppler shift simply doesn't work but the "expanding space" model is an exact match for what is observed.

Also redshift must be relative to the moving bodies i.e. take 3 bodies moving in the same direction along the same axis 1 moving at 100 2 (middle) moving at 70 3 moving at 40. These are all moving apart in the same direction and I think I am correct in saying the redshift from 2 - 3 and 2-1 would be the same.
Approximately, yes. Think in terms of angles between lines and it's fairly obvious (in relativity the angles add rather than speeds). You can think of galaxies "at rest" in expanding space like the points of drawing pins which are glued to the old "balloon model" (with the points outwards) and "proper motion" is like the point of one that is a little bent.

I am not disputing redshift just questioning if the interpretation is correct and all other possible causes have been checked and ruled out, possibly because I cannot see how space can just materialize out of nowhere ...
If you start with a little bit of 'nothing' and you want to have a lot of 'nothing' then you only need to add 'nothing' to it. What's the problem ;-)

There are many observational checks but two key ones are that cosmological redshift is the same for all frequencies (because the angle between the lines is the same) whicle all shifts caused by physical interactions varies with frequency (e.g. the colour of the light). The second key piece of evidence is that Type Ia supernovae near to use always last for a certain duration (they have a well defined light curve) while those at higher redshifts last longer. The reason is that by the time their glow is diminishing, they are farther away.
John15
#32
May9-12, 03:52 AM
P: 94
Many thanks George.
As far as expanding space goes if you add nothing to something then you are taking something away or rather negating it. Take an apple add nothing to part of it you are turning part of the apple into nothing so you end up with less apple not more, it would of course work if space was like elastic.
The atlas of the universe is most interesting, still not fully convinced that redshift is due to space expanding though as you zoom out it looks like many galaxies are close enough to be gravitationally bound, you mention the virgo and fornax clusters while far apart there is a fair number of galaxies inbetween, of course it would be easier if the strength of the various gravitational fields was included.
Really need a proper discussion to work out the implications.
elias2010
#33
May9-12, 04:38 AM
P: 32
Universe expansion



The sound waves are material (air) waves, so if we think that the Doppler Effect also acts on light waves, then light must be seen of the side of the particle (photon). Black holes in space prove that the light have a mass. Moreover the twin genesis effect shows us that a γ-photon has at least twice the mass of electron. In the phenomenon of fluorescence, for any absorbed photon a new one of lower energy is emitted. Lower energy (E) means lower frequency (ν): E=hν. But what is frequency meaning for one or a few photons? The question has been answered by Luis de Broglie since 1923: ν=mc2/h. So, it becomes obvious that frequency expresses the photon mass or size and thereby there are various photon sizes. That’s why its mass is not defined yet. Varying size is the reason for many observable effects, as the followings:
-Different refractive index of different colors
-Short radio waves reflection from the ionosphere
-Long radio waves large permeability (submarines radio)
Stars emit particles of all sizes such as UV-rays, X-rays, radio waves, γ-rays and ions. If an ion departs from a star and travels towards earth, except of a possible collision, it will arrive on earth integer, regardless to star’s motion. That is also true for a photon: we do not expect change its size on the way because the star is moving. A γ-photon emitted from a far star will not arrive on earth as an X-photon. An X-photon will not arrive as a UV-photon. Blue photons will arrive as they are and make man’s eye to feel the blue color. Therefore, any calculation based on redshift or blueshift is false. In 1980 Jan Claude Packard blames the cosmic dust for these. Now, his speculation becomes reasonable: Blue photons because of bigger size absorbed more by cosmic dust than the red ones. The bigger size, the much more collisions occur leading to higher absorbance. The longer distance among star and earth, there is more dust between them. The more dust between them, the less blue photons arrive on earth than the reds.
The radiation is continuous. The width of the wave is the number of photons per period (T). The wavelength is the size of photon.
Consequently, the supposed acceleration of the universe and the attendant concept of “dark energy” is a mistake.
Drakkith
#34
May9-12, 05:19 AM
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Sorry Elias, it is well known that light can be red or blue shifted by various methods. Most of your post contradicts known science and I advise you to learn more before attempting to tell us that a lot of what we know is incorrect.
GeorgeDishman
#35
May9-12, 06:56 AM
P: 255
Quote Quote by John15 View Post
Many thanks George.
As far as expanding space goes if you add nothing to something then you are taking something away or rather negating it. Take an apple add nothing to part of it you are turning part of the apple into nothing so you end up with less apple not more, it would of course work if space was like elastic.
No, you are left with one whole apple, no more, no less. There was a wink at the end of that comment though because it's a somewhat unscientific discussion but basically there is no reason why more vacuum shouldn't just appear since vacuum is crudely the absence of anything.

The atlas of the universe is most interesting, still not fully convinced that redshift is due to space expanding though as you zoom out it looks like many galaxies are close enough to be gravitationally bound, you mention the virgo and fornax clusters while far apart there is a fair number of galaxies inbetween, of course it would be easier if the strength of the various gravitational fields was included.
The impression I tried to give was of the relation to scale. Obviously the stars with the Milky way are bound, as are the planets in the solar system. For very widely separated clusters, the gravity falls roughly as the square of the distance while expansion increase in proprtion so there is some gap beyond which expansion will dominate. The exact value of that isn't too important and it would take a decent simulation to predict accurately for specific galaxies depending on their current velocities, but from previous discussions I believe it is around the scale I indicated.

Really need a proper discussion to work out the implications.
This is a good forum to do that, there are people here who really know their stuff (and many more like me just trying to catch up).
elias2010
#36
May12-12, 03:23 AM
P: 32
Dr Drakith,with all my respect,will you please answear my question instead of accusing me?
That was:
What frequency means for a photon or a few photons?
I only use existant theories.






"Sorry Elias, it is well known that light can be red or blue shifted by various methods. Most of your post contradicts known science and I advise you to learn more before attempting to tell us that a lot of what we know is incorrect. "


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