Expansion speeding up

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Expansion speeding up

Postby Auxradar » Tue Jul 21, 2015 9:19 pm

Could the increasing rate of expansion of the universe be explained by either the universe slowing down at an increasing rate from the outside in or similarly could it actually be imploding at increasing rate from the outside in. Has it actually been proven that everything is moving away from each other?
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Re: Expansion speeding up

Postby david48 » Mon Aug 10, 2015 6:12 pm

Auxradar wrote:Could the increasing rate of expansion of the universe be explained by either the universe slowing down at an increasing rate from the outside in or similarly could it actually be imploding at increasing rate from the outside in. Has it actually been proven that everything is moving away from each other?


As you rightly imply, It hasn't been proven that everything is moving away from each other. Such an idea results only from the "Red-Shift", which a purely optical phenomenon observed by using spectroscopes. There is no physical evidence for increasing distance between galaxies, stars and planets

The Red Shift could be accounted for in other ways. For example, by interstellar gas and dust absorbing and refracting photons as they cross the Universe. Thus slowing down the apparent speed of light. So lengthening its frequency, and making it appear more long-wave and hence "redder".
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Re: Expansion speeding up

Postby Gfamily2 » Tue Aug 11, 2015 2:53 pm

david48 wrote:
Auxradar wrote:Could the increasing rate of expansion of the universe be explained by either the universe slowing down at an increasing rate from the outside in or similarly could it actually be imploding at increasing rate from the outside in. Has it actually been proven that everything is moving away from each other?


As you rightly imply, It hasn't been proven that everything is moving away from each other. Such an idea results only from the "Red-Shift", which a purely optical phenomenon observed by using spectroscopes. There is no physical evidence for increasing distance between galaxies, stars and planets

The Red Shift could be accounted for in other ways. For example, by interstellar gas and dust absorbing and refracting photons as they cross the Universe. Thus slowing down the apparent speed of light. So lengthening its frequency, and making it appear more long-wave and hence "redder".


Alternatives to physical expansion have been proposed, but are not properly supported. How, for example, would refraction by interstellar gas and dust allow distant objects to produce pin sharp images?
There is evidence for the passage light through intervening clouds of neutral hydrogen, but this produces characteristic "Lyman alpha forest" spectra. You'll have to look that up on Wikipedia because I can't post urls.
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Re: Expansion speeding up

Postby voyager » Wed Aug 12, 2015 11:35 am

david48 wrote:The Red Shift could be accounted for in other ways. For example, by interstellar gas and dust absorbing and refracting photons as they cross the Universe. Thus slowing down the apparent speed of light. So lengthening its frequency, and making it appear more long-wave and hence "redder".


When you slow down light in a refracting medium, the waves actually bunch-up and increase its frequency! However, the slow-down compensates for the extra number of waves per second, effectively cancelling-out the change in wavelength, resulting in the refracted light having the same wavelength it had when it was originally absorbed...
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Re: Expansion speeding up

Postby david48 » Thu Aug 13, 2015 4:12 pm

But if this is true, why do simple (non-achromatic) lenses in refracting telescopes, produce "chromatic aberration" - ie changes in colour? Anyone who looks at the Moon through a telescope with a simple object-glass notices the changes in colour round the edge of the lunar image. The edge is sometimes bluish, and sometimes reddish, according to how you focus the eyepiece. The colour results from change of wavelength.

Surely such change wouldn't occur, if wavelength change is always cancelled out when light passes through the refracting medium of the telescope lenses?
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Re: Expansion speeding up

Postby voyager » Fri Aug 14, 2015 12:09 am

The colour spreading occurs because blue light slows down more than red light. If you then bring the red and blue back together, they would form the same white light that you started with. Here's an excellent article that explains this better than I can:
http://www.universetoday.com/121584/the ... e-rainbow/
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Re: Expansion speeding up

Postby david48 » Wed Sep 02, 2015 3:59 pm

voyager wrote:The colour spreading occurs because blue light slows down more than red light. If you then bring the red and blue back together, they would form the same white light that you started with. Here's an excellent article that explains this better than I can:
http://www.universetoday.com/121584/the ... e-rainbow/


Thanks Voyager, I read the article which you kindly provided.

It shows that the refraction of light is caused by its passage through a refracting medium.

This medium may be glass, water, air - or gas. Gas exists throughout the Universe, in the form of interstellar hydrogen. The hydrogen gas acts as a kind of ubiquitous, universal light-refracting medium.

Therefore, the light which we perceive from any source within the Universe, such as a star, has undergone refraction. This will change the colour of the light. Such colour change does not indicate anything about distance. Merely that the light has been refracted.

So I can't see why refraction of light should be equated with distance?
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Re: Expansion speeding up

Postby Gfamily2 » Wed Sep 02, 2015 11:33 pm

david48 wrote:Thanks Voyager, I read the article which you kindly provided.

It shows that the refraction of light is caused by its passage through a refracting medium.

This medium may be glass, water, air - or gas. Gas exists throughout the Universe, in the form of interstellar hydrogen. The hydrogen gas acts as a kind of ubiquitous, universal light-refracting medium.

Therefore, the light which we perceive from any source within the Universe, such as a star, has undergone refraction. This will change the colour of the light. Such colour change does not indicate anything about distance. Merely that the light has been refracted.

So I can't see why refraction of light should be equated with distance?

You have probably misunderstood.
The false colouring you get because of refraction is because different frequency light is refracted by different amounts. This is what gives chromatic aberration to objects in images of the moon, stars etc through a simple telescope
There is no change to the frequency of any particular 'photon' of light; simply that the different components get spatially separated when focussed.
"Refraction" is in no way an explanation for the cosmological red shift.
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Re: Expansion speeding up

Postby david48 » Thu Sep 03, 2015 7:12 pm

Gfamily2, yes, of course I understand that light gets refracted by passing through a simple medium.

Such as the simple crown-glass element of a non-achromatic refractor. As you say, this produces "chromatic aberration". The aberration makes the edge of the image look blue, or red, according to how the eyepiece is focussed on the image.

I saw this effect when I started observing, years ago, through a Charles Frank Junior Astronomical Telescope. When I looked at the Moon through it, the edge of the Moon could shift into acquiring a blue or red tinge, simply by adjusting the focus of the eyepiece.

This was a purely optical effect. It didn't make me think that a "blue shift" meant that the Moon was approaching the Earth. Or that a "red-shift" meant that the Moon was receding into the distance!

I understood that the effect was caused by refraction of light. Through the glass.

And so surely, a similar effect could be produced by refraction through the Hydrogen gas in the Universe?
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Re: Expansion speeding up

Postby Gfamily2 » Fri Sep 04, 2015 12:00 pm

david48 wrote:Gfamily2, yes, of course I understand that light gets refracted by passing through a simple medium.

Such as the simple crown-glass element of a non-achromatic refractor. As you say, this produces "chromatic aberration". The aberration makes the edge of the image look blue, or red, according to how the eyepiece is focussed on the image.

I saw this effect when I started observing, years ago, through a Charles Frank Junior Astronomical Telescope. When I looked at the Moon through it, the edge of the Moon could shift into acquiring a blue or red tinge, simply by adjusting the focus of the eyepiece.

This was a purely optical effect. It didn't make me think that a "blue shift" meant that the Moon was approaching the Earth. Or that a "red-shift" meant that the Moon was receding into the distance!

I understood that the effect was caused by refraction of light. Through the glass.

And so surely, a similar effect could be produced by refraction through the Hydrogen gas in the Universe?


You haven't understood where the colour comes from with refraction. You seem to think that red light passing through a glass can be changed into another colour 'by refraction'. It can't.
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