Is light stretched?

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Is light stretched?

Postby handmade on April 7th, 2017, 4:31 am 

Hello , I am new here, I read that the Universe is expanding and we observe this by the Hubble red-shift. From what I have read unless I am misunderstanding , red-shift is light being stretched .

Stretched from what exactly?
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Re: Is light stretched?

Postby BurtJordaan on April 9th, 2017, 5:25 pm 

It is more correct to say that large scale distances are increasing and this redshifts the light that travels across those distances. Things like "stretched space", "stretched light waves", etc. are sometimes used in analogies, but they typically just lead to misunderstandings.
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Re: Is light stretched?

Postby vivian maxine on April 10th, 2017, 12:48 am 

BurtJordaan » April 9th, 2017, 4:25 pm wrote:It is more correct to say that large scale distances are increasing and this redshifts the light that travels across those distances. Things like "stretched space", "stretched light waves", etc. are sometimes used in analogies, but they typically just lead to misunderstandings.


I did not know this. Thank you. A whole new story here.
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Re: Is light stretched?

Postby handmade on April 10th, 2017, 3:28 am 

BurtJordaan » April 9th, 2017, 4:25 pm wrote:It is more correct to say that large scale distances are increasing and this redshifts the light that travels across those distances. Things like "stretched space", "stretched light waves", etc. are sometimes used in analogies, but they typically just lead to misunderstandings.

Thank you for your reply, red-shift is a longer wave-length than blue, so to say light is red-shifted (stretched), it would have to be ''blue'' to begin with, so red-shift does not make entire sense to me because the light that travels through space is a mixture of frequencies and not ''blue''?
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Re: Is light stretched?

Postby BurtJordaan on April 10th, 2017, 3:45 am 

handmade » 10 Apr 2017, 09:28 wrote:Thank you for your reply, red-shift is a longer wave-length than blue, so to say light is red-shifted (stretched), it would have to be ''blue'' to begin with, so red-shift does not make entire sense to me because the light that travels through space is a mixture of frequencies and not ''blue''?

No, redshifted simply means that whatever wavelength was emitted is observed at a longer wavelength. We know the emitted wavelengths through spectral lines of the atoms and molecules found in galaxies and stars.
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Re: Is light stretched?

Postby handmade on April 14th, 2017, 6:08 am 

Thank you,

So you are saying that it is the emitted light from the body/galaxy that red-shifts, that makes more sense to me.


We do not observe any red-shift of space ?

We do not observe space expanding?
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Re: Is light stretched?

Postby BurtJordaan on April 14th, 2017, 6:43 am 

handmade » 14 Apr 2017, 12:08 wrote:So you are saying that it is the emitted light from the body/galaxy that red-shifts, that makes more sense to me.

Yes, it is the light that redshifts, but remember, the galaxy does not emit redshifted light in its own inertial frame. Then the light gradually redshifts as it travels towards us, because we are in a different inertial frame. Space per se does not redshift and we do not measure space to expand at all. We just measure the accumulated redshift and then we have to interpret that.

As I have said before, expanding space has all sort of potential for misinterpretation, because we can never measure any piece of space to expand. In natural coordinates (as we are used to on earth) we observe large distances to increase, because we 'see' them redshifted. It is what scientists call 'metric expansion' and it means that the universe is expanding at large scales, not at individual units of space level.
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Re: Is light stretched?

Postby handmade on April 15th, 2017, 7:22 am 

Thank you , quite clearly you have a good ability to explain things. I have spent several years arguing space itself does not expand as such.

You say we observe the light red-shifted that is travelling towards us, like wise the distance observer, the red-shifting body, must also observe the observer who is observing (us), to be also red-shifting?

On the premise of neither observer can tell who is moving.
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Re: Is light stretched?

Postby BurtJordaan on April 15th, 2017, 7:44 am 

Yes, we would appear redshifted by the same amount to any observer in that galaxy. Cosmological redshift does not indicate movement in space, just that the distance scale is expanding (metric expansion).

To be perfectly correct, there may a negligibly small movements relative to the universe at large for any galaxy, something called 'peculiar motion' in astronomy and cosmology. This is due to local inhomogeneity in the vicinity of one or both of the galaxies.
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Re: Is light stretched?

Postby handmade on April 15th, 2017, 9:59 am 

So how doe's red-shift show any sort of expansion? Surely the red-shift observed is because of the inverse square law of light?
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Re: Is light stretched?

Postby BurtJordaan on April 15th, 2017, 1:51 pm 

No, the inverse square law just makes light dimmer, it does not redshift the light, which is caused by an increase in the distance to the source over time. Read up a bit on cosmological redshift as well. Then ask questions on our Astonomy & Cosmology Subforum. This forum cannot explain all the details of any subject.
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