redshift = expanding universe?

[Moach]

help me understand something here....


i've been geeking out reading stuff ongeneralrelativity and the nature of the universe... as expected, the more i read, the more it becomes apparent just how little we really know about such things.... (i vote we need more spaceships :lol




but one thing struck me as odd -- there's a very large acceptance to the "expanding universe" theory, but i have only seen it being proved through interpretations of redshift and hubble's law as being caused by the doppler effect....


it does indeed make sense, that if the universe IS expanding, this redshift would be certaily accountable for...

but then, bear with me for a sec, for i'm told even Hubble himself didn't agree much with this at first -- what if it isn't expanding?


what it seems to me, (and i assume i'm generally mistaken) is that this is a confirmation-biased conclusion....

yes, if one starts from the notion that the universe expands, the redshift then proves it outright

but if one doesn't - then what could be the cause of said redshift?
could it not be simply due to the fact that lower-frequency waves contain more energy, thus can travel fiuther?

just as you hear a thunder as a muffled "boom" when its far, but it's more like a "crack" when up close... the higher-frequencies of the sound wave dissipate faster thann the lower ones...

can't the same happen with light?

in that case, Occam's razor suggests redshifts as described in hubble's law do NOT necessarily account for an expanding universe, but can certaily exist in a static one, being explained by the simple fact that "red" travels further than "blue" :hmm:


i'm not saying i think the whole theory is a bust, not at all.... i'm just a programmer with a hyperactive "geek gland"... i have no delusions of proving highly regarded theorists wrong or anything like that....


but then, what other evidence is there to the whole expansion thing? i don't think redshift alone quite cuts it, do you?



(just trying to learn here... please bash me down to bits gently)

 

[Jarvitä]

could it not be simply due to the fact that lower-frequency waves contain more energy, thus can travel fiuther?

No, red-shift means that the frequency of the radiation you're observing is higher than the frequency observed from its origin's frame of reference.

 

[Eli13]

But the discovery of red-shift assisted Edwin Hubble in making his theory on the expanding universe.

 

[Moach]

No, red-shift means that the frequency of the radiation you're observing is higher than the frequency observed from its origin's frame of reference.

wait what? :blink:


you have me terribly confused here? did you mean "wavelength" by any chance?

if an object is movng away, the observed frequency must be lower... wavelength is higher

is this not? :huh:

 

[Jarvitä]

Yes, you're right. I'm terrible at explaining physics in English.

However, your statement is still in error:

could it not be simply due to the fact that lower-frequency waves contain more energy, thus can travel fiuther?

The formula for the energy of a photon is [MATH]E=h\nu{}[/MATH], h being the planck constant and lowercase nu the frequency. Lower frequency means lower energy.

 

[Artlav]

It's a theory, and apparently the one that fits the facts better.

It's not red light being seen better, it's all the light getting redder.
There are some processes that emit light at precise frequencies, hydrogen absorption for example, supernovae light, etc.

The further away you look, the more this light is shifted towards red.
That's the observable fact.


If the universe is static, then we have some kind of an effect that reduces the energy of all EM waves.
This was resolved by assuming the change of the shape of space.

There are two ways it can happen - expansion or contraction.

Expansion feels logical to our cause-and-effect perception.
Then we have big bang in the past, the space itself expanding, universe created, and so on.
And space keeps expanding, so we see things far off being redder.

The problem is that the rate at which it appear to expand preclude the formation of galaxies - so we need to add dark matter to account for the mass.
And then the expansion appears to accelerate, so we add dark energy that repels stuff.
Last thing seems to be measurement error as recent findings show.

Symmetrically, space can be contracting.
The red shift will happen for exactly the same assumed reason.
The big bang will be in our future, and the past would be an image of what is called thermal death of the universe.

That resolves problems with the universe having had to be gravitationally bound - no need dark matter, and fit some other facts in, like pioneer anomaly.

The problem is that it's completely counter-intuitive, and would assume pre-determinism and completely different ideas of what time is.

Occam's razor worked here on some level - the most believable theory, expansion, is the mainstream.

But think for a moment, 6 billion years ago, all you see around you, all this complex stuff was just a gas cloud.
This gas cloud formed into planets, then into life, then into our technological structures.

If the universe itself is constantly expanding and falling apart, why do everything in it seem to fall together?

 

[Linguofreak]

in that case, Occam's razor suggests redshifts as described in hubble's law do NOT necessarily account for an expanding universe, but can certaily exist in a static one, being explained by the simple fact that "red" travels further than "blue" :hmm:

The thing is that different gasses, such as hydrogen, emit light in different frequency patterns. In the spectra of distant galaxies, these frequency patterns are shifted redwards. So we know that blue light isn't simply being filtered, but is actually becoming redder.

EDIT: Ninja'ed by Artlav.

 

[Moach]

The thing is that different gasses, such as hydrogen, emit light in different frequency patterns. In the spectra of distant galaxies, these frequency patterns are shifted redwards. So we know that blue light isn't simply being filtered, but is actually becoming redder.

EDIT: Ninja'ed by Artlav.

ninja'ed as you may have been - you present the exact answer i was loooking for


that makes some more sense - if the whole spectrum is redshifted, it really does call for something other than the usual "dissipation filtering" to be going on....


but still.... my "theorem of infinite physicist frustration", or "theory of eternal science work" remains solid - for every answer presented, there are n² new questions to be asked :lol:


at least we know - the answer is 42.... now to figure out what ever the question is...

 

[Linguofreak]

if an object is movng away, the observed frequency must be lower... wavelength is higher

One more thing: Cosmological redshift is *not* a Doppler shift. It is caused by the fact that the space that the light is traveling through expanding, not by a velocity difference between the observer and the observee. (It is often discussed in terms of velocity, though, since the distance between the two is in fact increasing, as it would if it were actually caused by a velocity difference).

The problem is that the rate at which it appear to expand preclude the formation of galaxies - so we need to add dark matter to account for the mass.

Not so. Dark matter was first inferred to exist from the fact that the observed orbital velocities of stars in galaxies can't be explained from the observed mass and location of the matter we can detect.

Some evidence for the *composition* of dark matter has come from things like galactic formation (the universe is too "clumpy" for it all to be from lightweight particles like neutrinos, and not clumpy enough for it all to be baryonic matter) and Big Bang nucleosynthesis (the ratios of isotopes in the universe are wrong for all the mass implied by the rate of expansion to be in the form of baryonic matter).

Symmetrically, space can be contracting.
The red shift will happen for exactly the same assumed reason.

I may be misreading you, but you seem to be implying that a contracting universe would have a cosmological redshift instead of a cosmological blueshift. I have *never* heard this. Do you have a source?

The big bang will be in our future, and the past would be an image of what is called thermal death of the universe.

That resolves problems with the universe having had to be gravitationally bound - no need dark matter, and fit some other facts in, like pioneer anomaly.

Not so, as said above, dark matter is needed to explain galactic rotation curves, among other things.

But think for a moment, 6 billion years ago, all you see around you, all this complex stuff was just a gas cloud.

The first galaxies are supposed to have formed around 13 billion years ago, and the Milky Way is supposed to be 8.8 ± 1.7 billion years old.

This gas cloud formed into planets, then into life, then into our technological structures.

If the universe itself is constantly expanding and falling apart, why do everything in it seem to fall together?

Because for close enough distances and heavy enough particles gravity and the electromagnetic force are strong enough to overcome the expansion.

 

[RisingFury]

i've been geeking out reading stuff ongeneralrelativity and the nature of the universe... as expected, the more i read, the more it becomes apparent just how little we really know about such things.... (i vote we need more spaceships :lol

Correction: ...just how little *you* really know about such things.

but one thing struck me as odd -- there's a very large acceptance to the "expanding universe" theory, but i have only seen it being proved through interpretations of redshift and hubble's law as being caused by the doppler effect....


it does indeed make sense, that if the universe IS expanding, this redshift would be certaily accountable for...

It's the other way around. Because the universe is expanding, because other galaxies are flying away, we get redshift. Expansion of the universe causes redshift, not the other way around.

And no, redshift isn't the only strong piece of evidence we have. I'm sure you've heard of the cosmic background microwave radiation. The famous picture that means nothing to the ordinary citizen:

It shows that the universe was once much hotter. You know what happens when hot, compressed gas expands, right? It cools... and that's exactly what we see today.

what it seems to me, (and i assume i'm generally mistaken) is that this is a confirmation-biased conclusion....

Like I said, redshift isn't the only bit of evidence we have.

yes, if one starts from the notion that the universe expands, the redshift then proves it outright

but if one doesn't - then what could be the cause of said redshift?
could it not be simply due to the fact that lower-frequency waves contain more energy, thus can travel fiuther?

Ugh......

First off, higher frequency photons carry more energy. As for penetration, the universe isn't that opaque.

And how do we know it's redshift and not... some other funky effect? I'm sure you've heard of emission and absorption lines in gas. If not:
Emission lines:

Absorption lines:

We know that for a certain element they're all at the same frequency. But when we see them move towards the red part of the spectrum, it means the object is moving away.

just as you hear a thunder as a muffled "boom" when its far, but it's more like a "crack" when up close... the higher-frequencies of the sound wave dissipate faster thann the lower ones...

can't the same happen with light?

It could and in air it does. The sky is blue because the blue light scatters before red one does. But the universe is far more empty. You do get some differences between red and blue light that make stars appear different colors, but we don't need to look at the color of light to know the redshift. We look at the emission lines. We see them move.

in that case, Occam's razor suggests redshifts as described in hubble's law do NOT necessarily account for an expanding universe, but can certaily exist in a static one, being explained by the simple fact that "red" travels further than "blue" :hmm:

I thought you'd have more respect for the difference between logical thinking and knowledge...

i'm not saying i think the whole theory is a bust, not at all.... i'm just a programmer with a hyperactive "geek gland"... i have no delusions of proving highly regarded theorists wrong or anything like that....


but then, what other evidence is there to the whole expansion thing? i don't think redshift alone quite cuts it, do you?

Redshift alone is a very powerful bit of evidence. You based your whole assumption on your ignorance, so I hope my posts explains a few things...

---------- Post added at 18:47 ---------- Previous post was at 18:27 ----------

The problem is that the rate at which it appear to expand preclude the formation of galaxies

No, not true. In local areas, gravity provides more pull than expanding universe.

- so we need to add dark matter to account for the mass.

The notion of dark matter was first introduced when first numerical simulations of galaxies indicated that galaxies with the mass of only the core + the stars should be unstable and should spin slower at the edge and not with a constant velocity.

Today we see plenty of evidence for dark matter, including bending of light around... nothing.

And then the expansion appears to accelerate, so we add dark energy that repels stuff.
Last thing seems to be measurement error as recent findings show.

Measurement error? That's a joke, right? Because a few days ago the Nobel Physics prize was awarded to the discovery of accelerated expansion of the universe, which implies dark energy.

That resolves problems with the universe having had to be gravitationally bound - no need dark matter, and fit some other facts in, like pioneer anomaly.

I'm sorry... Pioneer anomaly? Really? You're dragging that into the discussion?

It's funny, because all of the planets, comets and asteroids feel no anomaly, only our probes do. Keep in mind that all of them are powered by an RTG, which emits particles that can propel the probe.

Also, we don't need dark matter just to explain the universe. We know it's there. We just don't know what it is.

http://scienceblogs.com/startswithabang/upload/2009/04/colliding_dark_matter/galaxy_clusters.jpg[/quote]

See the smudged galaxies on the side of the middle one? It's the light from that same galaxy, being bent around.... nothing, it seems. Something is there that has mass, but does not interact with light.



[QUOTE="Artlav, post: 349045, member: 90"]The problem is that it's completely counter-intuitive, and would assume pre-determinism and completely different ideas of what time is.[/quote]

Right, so let's reverse time and it'll all make sense.



[QUOTE="Artlav, post: 349045, member: 90"]But think for a moment, 6 billion years ago, all you see around you, all this complex stuff was just a gas cloud.[/quote]

It only took about half a billion years for stars to form, a bit more for first galaxies to form. We know of galaxies that are over 13 billion years old! 6 billion years ago, the universe already looked largely as it does today.


[QUOTE="Artlav, post: 349045, member: 90"]If the universe itself is constantly expanding and falling apart, why do everything in it seem to fall together?[/quote]

The universe was never homogeneous. From the start, there were variations in density:

[img]http://www.computus.org/journal/wp-content/uploads/2008/08/cosmic_background_radiation.jpg

Variations are small, but large enough that in a local area, gravity could take over and create large structures we see today.

 

[Cras]

The concept of the expanding universe as it relates to the physical world is one that has not even come close to being understood. Some of the real cutting edge cosmology has some potentially shattering conclusions on what it means for the universe to expand, what happens when it does expand, and actually how it relates to contraction and the universe how it looked around the big bang.

But Dark matter and dark energy are things that are certain to exist, but so far have had much trouble figuring out what it infact is. We even have a map of a cluster of dark matter in a specific point in space so the debate of dark matter has certainly moved from "is it really there?" to the more direct question of "what is it?"

But to parrot the most mainstream theory of what dark matter is, it is the partner particles predicted by super symmetry, and the change in spin somehow makes it incapable of interacting with light.

 

[Artlav]

Disclaimer: Always treat what i say with a grain of skepticism, as i have a habit of expressing things in my own words and loosing a speculation or two in the mix.

Not so. Dark matter was first inferred to exist from the fact that the observed orbital velocities of stars in galaxies can't be explained from the observed mass and location of the matter we can detect.

I meant to say formation of galaxies in the form we have today.
There were problems with them getting that shape purely by the gravity alone, accounting only observed matter.

I may be misreading you, but you seem to be implying that a contracting universe would have a cosmological redshift instead of a cosmological blueshift. I have *never* heard this. Do you have a source?

Yes, i do. No, no specific source for that.
If we assume that he wavelength stay constant as the space shrinks, so when it hits something, it would be larger then originally.
Heard it in some mid-20th century discussion.

No idea how much sense it really makes, basically used it here as an example of how it could be other way around than expanding.

Not so, as said above, dark matter is needed to explain galactic rotation curves, among other things.

Roll a sheet of paper into a tight cylinder, and let it unroll. If the universe is contracting, then the shape is a given, whether gravitationally bound or not.

The first galaxies are supposed to have formed around 13 billion years ago, and the Milky Way is supposed to be 8.8 ± 1.7 billion years old.

I meant just planet Earth and the solar system, so it's about 5.

Because for close enough distances and heavy enough particles gravity and the electromagnetic force are strong enough to overcome the expansion.

Variations are small, but large enough that in a local area, gravity could take over and create large structures we see today.

Bigger picture - the things are constantly evolving, the complexity going up, gas cloud turns into humans.

I can't just disregard evidence like that on a mere chance, it's like disregarding the similarity of shapes of South American and African continental coast lines.

Measurement error? That's a joke, right? Because a few days ago the Nobel Physics prize was awarded to the discovery of accelerated expansion of the universe, which implies dark energy.

Not a joke.
Some research suggest it may be an illusion.
The error was in disregarding the speed of our local cluster relative to the background radiation, or something similar.
For example, http://cerncourier.com/cws/article/cern/29315

I'm sorry... Pioneer anomaly? Really? You're dragging that into the discussion?

I constructed an example of contracting universe for an alternative that fits most of the facts but looks different.

Magnitude of Pioneer anomaly is quite close to hubble's constant, and in contracting model this would be in the right direction.

See the smudged galaxies on the side of the middle one? It's the light from that same galaxy, being bent around.... nothing, it seems. Something is there that has mass, but does not interact with light.

I don't really understand this picture.
It proves there is something massive there that can't be directly observed.
Fits the description of dark matter.
Does not prove it's The dark matter functionally.

Right, so let's reverse time and it'll all make sense.

Naturally, people would prefer the theory that makes more sense, like the generally accepted expansion theory.

 

[RisingFury]

We only call it "dark" matter because we can't see it, but we know it's there. It's just a playful name. We don't know what it is, but we know it has mass. It tugs on galaxies, it bends light, it's there, but we can't see it.

You can't count Pioneer anomaly as evidence that our theories about gravity are bad. Why? Well, because we see that planets and other bodies are unaffected, because each of those probes had a possible source of thrust and because the anomaly has a different magnitude for each of the probes.

The simpler explanation here is that it's not our understanding about gravity that's wrong, but that there is a far more plausible explanation for it.


As for the paper...
There will always be doubt. When the first measurements came out, everyone hoped they were true, but were doubtful. But the measurement got confirmed by several different methods and the Nobel Physics prize was just handed out for it. This shows that the overwhelming majority of science supports the idea and a single paper won't overturn it.

 

[houseklh]

the universe is not expanding, the photons are just old and less energetic

The idea that our universe is expanding is wrong. The "proof" put forward is red-shift seen in distant objects - the more distant the object the more the red-shift. No doubt that motion of an object away from the subject does cause red-shift. But what about other things that cause red-shift?

My suggestion is that photons age and this creates the red-shift - the older the photon the more the shift. For example, a photon stream that starts out with a wavelength of 1000 nm, after a very long period of time will lose some of its energy and will shift to a longer wavelength, say 1000.1 nm.
I believe most of the red-shift we see in distant objects is this "old photon" red-shift.

What's the Achilles heel of the expanding universe theory? For uniform expansion of the universe the relative speed of objects moving apart has to be proportional to the distance between the objects. Let's say that for an object a finite distance away we determine a particular departure velocity. For an object twice that far away the departure velocity will be double. Now consider an object that is an infinite distance away. The departure velocity of this object will be infinite. This contradicts the law that says the speed of light cannot be exceeded.

Keith House 11-30-2011

 

[Cras]

Photons travel through space at C and thus do not travel through time, so they do not age.

And the laws of the speed of light is that no object can travel THROUGH SPACE faster than C, it says nothing about space it self expanding and making two objects travel faster than light. It is the same principle with probability wave collapse (if you subscribe to that interpretation of Quantum Mechanics).

There is no achilles heel of an expanding universe, there is no reason why it should not expand, aside for the uncomfortable feeling it gives humans, such as Einstein himself, which is why he insisted on a Constant to General Relativity.

But to clarify it again, the model of an expanding universe in no way shape or form violates special relativity and the speed of light limit.

The real question is why the universe has falled back to an inflationary behaviour after the big bang. The current model is the the big bang created the expansion of space, and did so in an inflationary manner, but did not infact create the universe. At some point, the negative pressure of the big bang's cause disappated and gravity turned from repulsive to the attractive force we are all familiar with. Is it possible that on cosmic scales, that negative pressure has risen again and causes space at these large scales to again be repusled by gravity?

And the other question, is there a limit to expansion? Some suggest that at a certain point, expansion will actually be percieved as contraction, and the universe will begin to appear to be falling upon itself, not by a new addition of force, but rather by interpretation and perception of what is actually going on in terms of energy.

But the argument that the universe is static is one that has long been abandoned. The universe is indeed expanding, and to this there is no question.

 

[RisingFury]

The idea that our universe is expanding is wrong.

Keith House 11-30-2011

The Nobel Physics prize got handed out a few weeks ago for the discovery of accelerated expansion of the universe.

Of course, the armchair astronomers, Wikipedia physics experts know better.

 

[Linguofreak]

The idea that our universe is expanding is wrong. The "proof" put forward is red-shift seen in distant objects - the more distant the object the more the red-shift. No doubt that motion of an object away from the subject does cause red-shift. But what about other things that cause red-shift?

Firstoff, this thread had been dead for almost a month.

Secondly, the expansion of the universe is one of those "other things that cause redshift".

My suggestion is that photons age and this creates the red-shift - the older the photon the more the shift. For example, a photon stream that starts out with a wavelength of 1000 nm, after a very long period of time will lose some of its energy and will shift to a longer wavelength, say 1000.1 nm.
I believe most of the red-shift we see in distant objects is this "old photon" red-shift.

As has been said, this doesn't work. Because of the effects of relativity, photons do not experience time.

What's the Achilles heel of the expanding universe theory? For uniform expansion of the universe the relative speed of objects moving apart has to be proportional to the distance between the objects. Let's say that for an object a finite distance away we determine a particular departure velocity. For an object twice that far away the departure velocity will be double. Now consider an object that is an infinite distance away. The departure velocity of this object will be infinite. This contradicts the law that says the speed of light cannot be exceeded.

The thing is that General Relativity allows for ways for the distance between two objects to increase without either of the objects moving (in fact, velocity is a fuzzy concept in General Relativity for objects that are not right next to each other), and the rate at which the distance between two objects can increase is not limited by the speed of light. The expansion of the universe has nothing to do with objects "moving away from each other", but rather is one of these processes by which the distance between object A and object B can increase without any relative motion between the two.

 

[Urwumpe]

Also, you violate the laws of thermodynamics with your aging photons. And you know what this means. Instant punishment by spontaneous combustion.

No, joke aside: The energy that a photon transports is defined by its wavelength. The shorter the wavelength, the more energy it carries. If aging photons would increase their wavelength, there would be energy getting transmitted from the photons to... where?

Also, much more important: The photons of radio transmissions from Earth to spacecraft or back do not show any form of such aging. There is only the known relativistic Doppler shift, you have actually less error in measuring the velocity of a spacecraft by using the doppler shift of the carrier signal, than by using impulses and the run time to measure the change in pseudorange.

(And signing your posts with your name and the date you posted it is a sign of beginning insanity. It is the internet. Use a license.)

 

[Gumok]

What about that energy of photons is going to another dimension? So slowly but enough for red shift? :hmm:

 

[Urwumpe]

What about that energy of photons is going to another dimension? So slowly but enough for red shift? :hmm:

Problem: Which other dimension?

You could also claim it goes to make angels sing. Same problem. It is not really scientific to explain things with hypothetical entities, if you are strict it is even unscientific.

The redshift by Doppler effect works without hypothetical entities and can be experimentally tested. We use it already well for laser gyroscopes.