Is the Universe Expanding or Has it Already Expanded?

[GeorgeDishman]

George the first explanation 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 explanation 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]

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]

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]

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]

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]

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 existent 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. "

 

[marcus]

What frequency means for a photon...?

It means its energy.

You know the electromagnetic field has both wavelike and particle-like aspects.
We can make a lightsource so dim that it only sends one photon at a time---say approx one photon per second.

We can send that thru a double slit and onto a screen where there are detectors. A detector is clicking only once or less per second.

By comparing which detectors where on the screen click we can discover an interference pattern of stripes as if each individual photon was acting like what we call a wave

And the wavelength we discover (from the stripes) to be proportional to the ENERGY of the individual clicks (a detector can be like a photocell that measures energy delivered to it)
as if the field were delivering energy in discrete bits, and nevertheless was like a wave.

From the wavelength, knowing the speed, we can tell the frequency. The frequency of that discrete bit of energy that was delievered by the field.
The frequency is proportional to the energy that was delivered---proportional by Planck constant.
Multiply the Herz by Planck's constant and you get the Joules. It's basically the same thing.

There are no particles really. There is only the field. The field acts like a wave (in the doubleslit apparatus) but it also delivers energy in discrete clicks. So it is not exactly like a wave we usually think of. Nor exactly like the little beans we naively picture when we speak of particles.
The field does not care how we imagine it. In reality it is neither naive picture, neither beans or ripples.

I think you know all this, so why would you ask? Of course you know what the frequency is. It is the energy delivered when there is a click!

I think this is off-topic in a Cosmology thread, Elias. You could get more discussion in Quantum forum, if you want it.

 

[elias2010]

Of course,and you know that E=mc2 and E=hν.De Broglie combined both equations at 1923:λ=h/mc or ν=mc2/h
Begining of this,I retype my question as you prefer:
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 loose its energy on the way because the star is moving.
Thank you for the advices.

 

[marcus]

we do not expect loose its energy on the way...

energy conservation does not hold in expanding geometry
who is "we"?

CMB photons were emitted at 3000 kelvin and are now 2.75 kelvin blackbody radiation.
They have lost more than 999/1000 of their original energy.

We've discussed this before at the forum. We DO expect the photon to lose energy on its way.

Some folks might enjoy this blog post (it has a picture of Emmy Noether):
http://cosmic-horizons.blogspot.com/2011/11/conservation-laws.html

 

[Mark M]

To elaborate on what Marcus just said above, photons lose energy with the metric expansion of space. If you imagined a normal object traveling along expanding space, its speed would change - but as you know, the speed of light is invariant. Hence, as light travels through an expanding universe, its wavelength is increased. In terms of photons, wavelength is inversely proportional to energy by Planck's equation E = \frac {hc} { \lambda}

 

[GeorgeDishman]

Of course,and you know that E=mc2 and E=hν.De Broglie combined both equations at 1923:λ=h/mc or ν=mc2/h

E=mc² applies only to particles which have non-zero mass. De Broglie's forula tells us their wavelength but you can't use it for a photon, photons have zero mass.

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.

The kinetic energy of the particle measured on Earth is less than that measured relative to the source.

That is also true for a photon: we do not expect loose its energy on the way because the star is moving.

Consider a photon emitted from a star in our own galaxy that happens to be moving away from us. It doesn't lose energy en route, but the frequency we measure here is less than that measured relative to the emitting star because of the Doppler effect.

In both cases, the energy is frame dependent. Cosmological redshift has a slightly different cause (see the posts by others for that) but the result is the same, the frequency received is less than that emitted. Inbetween, the frequency depends on the proper motion of the observer.

 

[Matt Benesi]

Bleehhhh... anyways. Durp.

 

[Drakkith]

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 existent theories.

I'm sorry but the only questions I saw in your earlier post you answered yourself. However, as has been answered, frequency is the numbers of oscillations of the electric and magnetic field per second of a photon, which also corresponds to the amount of energy carried by said photon.

Of course,and you know that E=mc2 and E=hν.De Broglie combined both equations at 1923:λ=h/mc or ν=mc2/h
Begining of this,I retype my question as you prefer:
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 loose its energy on the way because the star is moving.
Thank you for the advices.

The energy of the ion will be different depending on if you are moving away from or towards the Sun (Or if the Sun is moving away from or towards you). Similarly the energy of a photon will change as well. In addition, the expansion of the universe causes a redshift of light over huge distances, resulting in light losing it's energy over millions to billions of years of travel.

 

[Naty1]

from a post above

we do not expect loose its energy on the way...

and a reply

energy conservation does not hold in expanding geometry
who is "we"?

CMB photons were emitted at 3000 kelvin and are now 2.75 kelvin blackbody radiation.
They have lost more than 999/1000 of their original energy.

These are two different ways of looking at the same phenomena:

https://www.physicsforums.com/showthread.php?t=162727&highlight=current+flow&page=4

[In the great 2007 thread Wallace, Chronos and Oldman take a different view than expressed here [and there] by Marcus...you can read the posts from the 40's thru 50's and see the pros and cons. ]

I do think it is better to think of (photons) as being redshifted by being observed in a different frame ...Now at t ticks along, the scale factor a(t) increases. Therefore two observers who are both at rest wrt to the CMB, but who have different times t will therefore be in different frames (have different metrics). This is what leads to photons being redshifted when observed and emitted at different times.

...two observers who are both at rest wrt to the CMB, but who have different times t will therefore be in different frames (have different metrics). This is what leads to photons being redshifted when observed and emitted at different times...

I tend to agree, photons are not redshifted by traveling through the universe, they are redshifted only because they are observed in a different frame from what they are emitted in.

Marcus: # 48] I am not comfortable with that because among other things I see cosmologists doing inventories of the energy density which are implicitly estimated IN A CMB FRAME...

These 'conflicting' viewpoints stem from this as explained by Chalnoth elsewhere:

" … You get some total redshift for faraway objects due to cosmological expansion. How much of that redshift is due to the Doppler shift# and how much is due to the expansion between us and the far away object is completely arbitrary."

# Doppler shift is based on relative velocity frame based differences.

You takes your pick!

 

[elias2010]

Did n't black holes prove that the photons have a mass?
Anyway,provided that they have not mass,why do you believe that the Doppler effect whitch acts in material waves has to act in non-material waves ( the light waves as you claim) too?

 

[bapowell]

Did n't black holes prove that the photons have a mass?

Where does this come from?

Anyway,provided that they have not mass,why do you believe that the Doppler effect whitch acts in material waves has to act in non-material waves ( the light waves as you claim) too?

Why do you think that the Doppler effect is only relevant to "material" waves?

 

[Whovian]

Just to make bapowell's comment perfectly clear:

Photons, in their rest state, are massless (though they do have a mass when moving at the only speed they're observed at, c, but this has nothing to do with the fact that they're affected by gravity.)

Define "material waves." Do you mean matter waves? In which case, why should the Doppler Effect only affect matter waves? A good understanding of why it arises should make it clear that this isn't the case.

 

[GeorgeDishman]

Just to make bapowell's comment perfectly clear:

Photons, in their rest state, are massless (though they do have a mass when moving at the only speed they're observed at, c, but this has nothing to do with the fact that they're affected by gravity.).

Just to make it clearer, mass is a scalar quantity hence is invariant. The formula for calculating mass for a moving particle of any type at any speed is:

m² = E² - |p|²

where E is the energy and |p| is the magnitude of the momentum.

For a photon, theory says E=|p| so m=0.

Actual measurements can only place an upper limit on this due to the finite accuracy of all instruments:

http://en.wikipedia.org/wiki/Photon#Experimental_checks_on_photon_mass

 

[elias2010]

In which case, why should the Doppler Effect only affect matter waves?
Because this only is experimentally assured.The other is a speculation whitch universe expansion is based on.

 

[Ich]

Because this only is experimentally assured. The other is a speculation whitch universe expansion is based on.

Huh?
Ever got a speeding ticket?

Is it really too much effort to read e.g. the Wikipedia article on the Doppler effect before you make such allegations?

 

[Whovian]

In which case, why should the Doppler Effect only affect matter waves?
Because this only is experimentally assured.The other is a speculation whitch universe expansion is based on.

a) The Universe's expansion is not based in any way on the Doppler Effect. The Doppler Effect does give us evidence for it, but General Relativity alone is enough to demonstrate the existence of the Big Bang.

b) The Doppler Effect applies to all wave phenomena, and as I have mentioned before, a good understanding of why it arises should make this clear. Simple mathematics are enough to prove its existence for all waves and wave pulses. It's not experimentally assured, it's mathematically assured. And while all our evidence of the physical world is based on what you can derive from theories, we have good evidence that waves exist in the Universe, in the case of both matter and light waves, which, again, the Doppler effect applies to.

 

[elias2010]

Just to make bapowell's comment perfectly clear:

Photons, in their rest state, are massless (though they do have a mass when moving at the only speed they're observed at, c, but this has nothing to do with the fact that they're affected by gravity.)

Define "material waves." Do you mean matter waves? In which case, why should the Doppler Effect only affect matter waves? A good understanding of why it arises should make it clear that this isn't the case.

Because matter waves don't propagate in vacuum like the light waves.They spread in a physical medium,the air for example.It is the medium whitch periodically pressed and depressed by the source.When the source is moving towards a receiver,the air between is temporarily pressed.
On the other hand,light waves is radiation.Neither they or empty space can be pressed.

 

[elias2010]

energy conservation does not hold in expanding geometry
who is "we"?

CMB photons were emitted at 3000 kelvin and are now 2.75 kelvin blackbody radiation.
They have lost more than 999/1000 of their original energy.

We've discussed this before at the forum. We DO expect the photon to lose energy on its way.

Some folks might enjoy this blog post (it has a picture of Emmy Noether):
http://cosmic-horizons.blogspot.com/2011/11/conservation-laws.html

Where goes the lost energy?
In case of blueshift photons gain energy.Where does this energy comes from?
Can stable motion (moving star, not accelerating) produce energy?

 

[elias2010]

a) The Universe's expansion is not based in any way on the Doppler Effect. The Doppler Effect does give us evidence for it, but General Relativity alone is enough to demonstrate the existence of the Big Bang.

b) The Doppler Effect applies to all wave phenomena, and as I have mentioned before, a good understanding of why it arises should make this clear. Simple mathematics are enough to prove its existence for all waves and wave pulses. It's not experimentally assured, it's mathematically assured. And while all our evidence of the physical world is based on what you can derive from theories, we have good evidence that waves exist in the Universe, in the case of both matter and light waves, which, again, the Doppler effect applies to.

Zenon's paradox teach us that a "mathematical proof" can easily lead us to a mistake.

 

[Whovian]

Zenon's paradox teach us that a "mathematical proof" can easily lead us to a mistake.

Zeno's Paradox is completely unrelated to the topic at hand.

Because matter waves don't propagate in vacuum like the light waves.They spread in a physical medium,the air for example.It is the medium whitch periodically pressed and depressed by the source.When the source is moving towards a receiver,the air between is temporarily pressed.
On the other hand,light waves is radiation.Neither they or empty space can be pressed.

Okay, and when the source is moving towards you, the peaks of the wave get closer together, since the source has moved closer to you by the time it emits the second peak. This is the Doppler Effect.

 

[bapowell]

Where goes the lost energy?
In case of blueshift photons gain energy.Where does this energy comes from?
Can stable motion (moving star, not accelerating) produce energy?

First, energy is not globally conserved in general relativity. There is extensive information on this topic here on the forums and on the web.

With regards to blueshift, indeed, the photon must gain the energy from somewhere.

A moving star *has* energy, called kinetic energy. It doesn't produce it.

 

[bapowell]

Zenon's paradox teach us that a "mathematical proof" can easily lead us to a mistake.

On the contrary. Mathematically, series calculus provides a solution to the paradox. To which mistake are you referring?

 

[bapowell]

Because matter waves don't propagate in vacuum like the light waves.They spread in a physical medium,the air for example.It is the medium whitch periodically pressed and depressed by the source.When the source is moving towards a receiver,the air between is temporarily pressed.
On the other hand,light waves is radiation.Neither they or empty space can be pressed.

Okay, but what does the compression/rarefaction of the supporting medium have to do with the Doppler effect?

 

[elias2010]

First, energy is not globally conserved in general relativity. There is extensive information on this topic here on the forums and on the web.

With regards to blueshift, indeed, the photon must gain the energy from somewhere.

A moving star *has* energy, called kinetic energy. It doesn't produce it.

From where it gains the energy? From the (because of) star's motion?
If this energy is irrelevant to star's motion,then you can't make estimations for it's motion by the change in energy.

 

[elias2010]

Zeno's Paradox is completely unrelated to the topic at hand.



Okay, and when the source is moving towards you, the peaks of the wave get closer together, since the source has moved closer to you by the time it emits the second peak. This is the Doppler Effect.

In the case of one photon where do you see the waves?