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high redshift mirrors

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- Wed, 06 Mar 2019 13:31:08 EST wIGiff+l No.57553
File: 1551897068878.jpg -(342947B / 334.91KB, 1000x1000) Thumbnail displayed, click image for full size. high redshift mirrors
lets say you were able to place a mirror in space out at such a distance that the mirror experience cosmological redshift from your perspective. If you were to shoot a laser beam of some wavelength at the mirror then the light reflecting off the mirror would be a longer wavelength than the originating laser because of the relativistic doppler effect.
what wavelength would the light be when it got back to you after bouncing off the mirror? would it be the original wavelength or would it be redshifted?
if its not the original wavelength then how was energy conserved?
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Grote Reuber - Wed, 06 Mar 2019 19:42:58 EST 457vC2+I No.57555 Reply
My understanding is that the round trip photons would be redshifted twice as much as the mirror. The light the mirror reflects from a nearby source would be the source of its apparent redshift. The laser point on the mirror would have the same redshift as the mirror, and on an identical mirror near the emitter the round trip photons have undergone twice the amount of elongation of their wavelength due to the doubled distance of their journey.
Energy is conserved because the photon never actually loses energy throughout its journey, it just comes to occupy a larger wavelength. The same is true however far you follow the photons originally from the mirror or the round trip set, except as you went further and further out the difference between their amounts of shift would be less and less. A photon just on the edge of the cosmological horizon has its wavelength stretched out so long that the photon right behind it, even if part of a laser, is so much longer than the one before it that it will never reach the observer in the lifetime of the universe. So in general energy is conserved in the same way that the law of inverse squares counter-intuitively describes the way an equal force is conserved over an expanding area; nothing is lost, it's just more spread out.
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Stephen Hawking - Wed, 06 Mar 2019 22:15:47 EST NqnehfXO No.57556 Reply
>>57555
The energy conservation part was what interests me most. The photon exits at 2000Å and comes back at 8000Å, having doubled in wavelength twice.
Where did 3/4 of it's energy go to? It didn't have to climb out a gravity well or anything like that.
Also what do you thing happens to a photon when it's wavelength exceeds the Hubble length? Can it just be anywhere it wants to be ASAP?
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Grote Reuber - Thu, 07 Mar 2019 14:11:12 EST 457vC2+I No.57569 Reply
>>57556
>>Where did 3/4 of it's energy go to? It didn't have to climb out a gravity well or anything like that.
The energy didn't go anywhere, it's still there. It's just stretched out over a larger area, so its density is less. Color is essentially a measure of the density of photon waves. Consider that you could get the same degree of burn by sitting under an infrared lamp for hours as you could by being hit by a UV laser for a few seconds. Same burn, same energy transferred, different wavelengths, different time.

>>Also what do you thing happens to a photon when it's wavelength exceeds the Hubble length?
Well time is a factor. The wavelength of even the most redshifted photon is so much smaller than the hubble volume that by the time you encountered photons that were that stretched out, your cosmic horizon would have receded even further, so they would never reach you. I think you would only encounter such photons from bodies that were formerly blue-shifted relative to you, such that your relative velocity is less than the rate of cosmic expansion.
>>Can it just be anywhere it wants to be ASAP?
Naw, it would just be observable for an incredibly long time, but the bow wave would still only be moving at c. However, it does present three interesting questions. In the very late universe when the cosmic horizon is quite small, and there are lots of old redshifted photons much larger than that time's hubble volume, as a photon is transiting the volume, is it detectable if both its start and end points exist outside the cosmic horizon? And what redshift does it have when observed -- that of its total wavelength, or only the portion within the cosmic horizon? Lastly, since we know that on cosmological scales the value of c fluctuates, both through time and also apparently through space, what happens when a photon is so stretched out that it is experiencing different values of c along its length? How would the 'tensile stress' or 'compression/expansion' on the photon be manifested?
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Johann Bode - Sat, 09 Mar 2019 03:40:52 EST UtRhpzbE No.57570 Reply
>>57569
Is the lost energy then contributing to the cosmic microwave background radiation? Or is the CMBR an image of the decoupling epoch seen at high redshift?
Theres information lost in redshifting too, if we'd laser'd an image off the mirror instead of a dot then the returning image would be both dimmer and less distinct because of the redshifting. Imagine the size of telescope you'd need to observe hubble volume wavelength photons. The energy of the quanta would be so tiny that even with a telescope the diameter of the universe they'd still be challenging to detect.
That may well be the end game of this universe if we ever do get off this rock, once we're done using our eventual mastery of physics to shape galaxy clusters into penises for the lulz people will probably get back to the big telescope competition. Eventually a telescope the mass of the universe will be constructed and someone will fuck up a metric-imperial conversion and the whole thing will collapse on itself and start a new big bang.
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Maximilian Wolf - Mon, 11 Mar 2019 21:50:39 EST 457vC2+I No.57571 Reply
>>57570
>>Is the lost energy then contributing to the cosmic microwave background radiation? Or is the CMBR an image of the decoupling epoch seen at high redshift?
Both, sort of, I think. The CMB we see is the redshifted light from photons whose source star/event is beyond the cosmic horizon, which is itself sort of that decoupling bowshock.

>>Theres information lost in redshifting too
Well there's signal lost to noise in any transmission, but the information isn't lost to the universe, just to some observer, who could theoretically reconstruct the information of the original transmission if they knew every source of noise it was subject to, redshift included.

>>Eventually a telescope the mass of the universe will be constructed and someone will fuck up a metric-imperial conversion and the whole thing will collapse on itself and start a new big bang.
Most plausible universe origin story I've heard lately.
>>
Georges-Henri Lemaitre - Sun, 17 Mar 2019 21:43:06 EST aGo2dCNY No.57575 Reply
>>57571
I read some more about the background radiation and it turns out that observing things at great distances is a challenge, which brings me to the second point, which is I'm fairly convinced that what you suggested about de-redshifting an image to sharpen it up isn't possible. The reason I say that is that there is a fundamental relationship between the aperture of any detecting device and the wavelength being detected. The number of waves that can bridge the aperture is what determines the limits of resolution of the image. If you were to get an image and de-redshift it by squeeze the wavelength back to the original size then you would effectively be observing waves which were falling outside of the detecting equipment's aperture and energy wouldn't be conserved.
I've found it funny for a long time ever since I learned about this junction of optics and redshift, things that are moving away from you at high velocity lose visual definition because of the relativistic doppler effect. Given this being the case it means that a space telescope which could be accelerated to relativistic velocity could observe much much deeper into the universe in it's direction of travel once it reached a badass enough rest frame. Once it was done observing it could turn around and do a another observation in the opposite direction ending up nearby Earth and drop off the data. The high flux densities being observed and the lower wavelength of observation would make some very interesting images. Transluminal Schmidt camera go go go! Like a giant Pac Man eating up all the photons he encounters along the way.
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Charles Bolton - Mon, 18 Mar 2019 23:04:12 EST 457vC2+I No.57576 Reply
>>57575
>>de-redshifting an image to sharpen it up isn't possible.
That's not quite what I'm saying. I'm not saying that such an instrument is physically possible, just that it's theoretically possible. It's practically impossible to ever know 'all sources of noise' for a signal, but that doesn't mean the information was destroyed, just become irretrievable. Signal processing algorithms already work this way, by attempting to measure known sources of noise and working backwards to reconstruct the original information. But...

>> you would effectively be observing waves which were falling outside of the detecting equipment's aperture and energy wouldn't be conserved.
Only effectively, you're actually only observing the photons within the aperture, then using other energy to do computation to modify that information. You don't retrieve the original photons, you're just able to deduce what information they contained (with some error based on the imperfection of your understanding of sources of noise.) So energy is still conserved.

>>could observe much much deeper into the universe in it's direction of travel once it reached a badass enough rest frame.
Perhaps, but wouldn't you then begin to lose visual definition to blueshift? Still would be a pretty sweet telescope, and the amount you lose to blueshift might be negligible enough to still make it superior relatively.
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Friedrich von Struve - Tue, 19 Mar 2019 07:34:25 EST izGRJ+VN No.57577 Reply
>>57575
I don't think there is any information lost from redshift. It's the underlying space that is expanded during redshit, not the lightwave itself.
If you are in a reference frame that negates that expansion, you get exactly the "original" wavelength.

So I think this "relativistic reference frame" telescope would theoretically work.
There are some practical considerations though:
Pointing a telescope in the direction of travel means it is exposed to all the interstellar dust.
So you maybe need a vanguard of other ships that absorb it so it doesn't wreck you instruments.
Apart from that I think we could actually calculate if it's feasible to move that fast at all, drag of the interstellar medium becomes significant once you hit a considerable fraction of c.
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Charles Bolton - Tue, 19 Mar 2019 19:11:02 EST 457vC2+I No.57578 Reply
>>57577
In star trek sci fi shows they use electromagnetic fields to control interstellar dust. Could it be simple as ionizing the telescope? Also, though it would negate some of the benefits of having a large aperture to observe large wavelengths, if the telescope was quite small it might be possible for it to exist entirely within the bowshock of a forward facing shield. Would limit its field of view, but directly forward objects might not be the ideal candidates anyway because of the blueshift thing.
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Paul Goldsmith - Wed, 20 Mar 2019 05:55:06 EST 4o5sH+7r No.57579 Reply
>>57577
>Pointing a telescope in the direction of travel means it is exposed to all the interstellar dust.
destroy everything in your path using the power of relativistic beaming
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Johannes Kepler - Wed, 09 Oct 2019 01:24:51 EST aGo2dCNY No.57817 Reply
>>57815
i'm permanently banned from all google platforms including youtube, would you be willing to describe the contents of the video for me or upload it to somewhere thats not google owned so i can view it?
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James Christy - Fri, 11 Oct 2019 06:57:14 EST JvOVK4Sl No.57819 Reply
>>57817
Jesus Christ did you attempt to complete Operation Glowing Dove on them?
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Jist - Tue, 15 Oct 2019 15:30:24 EST HeCUPa43 No.57820 Reply
>>57553
Sounds like you fell into some distinction between quatem particals, and what happens with what lies in the scope of a laser pointer .
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Gerard Kuiper - Thu, 28 Nov 2019 22:23:21 EST KagVVlp+ No.57872 Reply
1574997801470.gif -(549715B / 536.83KB, 256x192) Thumbnail displayed, click image for full size.
>>57817
>i'm permanently banned from all google platforms
I'm just DYING to hear this story.

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