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Second, is this wave length (or half wave length) the longest possible wave length--excluding the fact that the universe is expanding and the wave length can lengthen.

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- Thread starter edearl
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- #1

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Second, is this wave length (or half wave length) the longest possible wave length--excluding the fact that the universe is expanding and the wave length can lengthen.

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https://www.physicsforums.com/showthread.php?t=110906

If your asking whether its possible for a single photon to span the universe. That depends on the speed of expansion of the universe. If both sides are approaching the speed of light, then no.

EM waves are calculated by wavelength=velocity/frequency. Since nothing can exceed the speed of light, you are trying to determine if you could have a frequency which is practically zero. Theoretically, if the universe is of finite size, and you are capable of getting a zero frequency, then the size of the wavelength isn't constrained by the size of the universe.

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https://www.physicsforums.com/showthread.php?t=110906 says, "1) Theres no theoretical upper limit on the wavelenght of the EM-spectrum. On the horizon of our visible universe theres an barrier of "infinite redshift". Also, EM-radiation radiated by a body falling into a black hole will also redshift into "infinity" at the event horizon," which I assume is true as time increases because the event horizon is expanding at the speed of light. However, my question was limited to a time t_n. If a photon with wavelength longer than the size of the observable universe existed, then there are two possibilities AFAIK: 1) part of that wave must exist outside the event horizon. 2) The wave must reflect back into the observable universe at the event horizon. Since there is infinite redshift at the event horizon, the wave would presumably be absorbed rather than reflected. Both of my two possibilities seem to me to be impossible. Thus, the reason for my question. Since QM is often not intuitive, I expect the answer to be something else.

https://www.physicsforums.com/showthread.php?t=110906

If your asking whether its possible for a single photon to span the universe. That depends on the speed of expansion of the universe. If both sides are approaching the speed of light, then no.

EM waves are calculated by wavelength=velocity/frequency. Since nothing can exceed the speed of light, you are trying to determine if you could have a frequency which is practically zero. Theoretically, if the universe is of finite size, and you are capable of getting a zero frequency, then the size of the wavelength isn't constrained by the size of the universe.

The event horizon of the universe is smaller than the size of the universe and is (according to http://universe-review.ca/F02-cosmicbg.htm) "the distance to which light can have traveled since the universe originated."

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Zz.

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Based on a gravitational redshift, you have a downhill region (inside blackhole), an uphill region (outside of blackhole), and a region at the top of the hill (event horizon).

Redshift relates to z=(observed wavelength-wavelength at emmision)/(wavelength at emmision)

So if you can get the wavelength at emission equal to zero, you can get an infinite redshift.

http://en.wikipedia.org/wiki/Gravitational_redshift

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I did not think of an infinite redshift and infinite wavelength within a finite universe as possible; thus, it took a while to wrap my mind around it. It makes more sense than anything I thought of. Thanks.

Based on a gravitational redshift, you have a downhill region (inside blackhole), an uphill region (outside of blackhole), and a region at the top of the hill (event horizon).

Redshift relates to z=(observed wavelength-wavelength at emmision)/(wavelength at emmision)

So if you can get the wavelength at emission equal to zero, you can get an infinite redshift.

http://en.wikipedia.org/wiki/Gravitational_redshift

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http://physics.bu.edu/~duffy/py106/EMWaves.html

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