Is there any theoretical end to the electromagnetic spectrum…
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1$\begingroup$ perhaps when the energy density due to the photon becomes so high that electroweak symmetry is restored ? That would make electromagnetism obsolete. $\endgroup$– tobaltCommented May 16, 2022 at 4:03
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2$\begingroup$ @GedankenExperimentalist I believe then the wavelength becomes too long that it extends beyond our cosmological horizon. $\endgroup$– TriatticusCommented May 16, 2022 at 4:36
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$\begingroup$ Possible duplicates: physics.stackexchange.com/q/159922/2451 , physics.stackexchange.com/q/43063/2451 , physics.stackexchange.com/q/128340/2451 and links therein. $\endgroup$– Qmechanic ♦Commented May 16, 2022 at 8:14
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1$\begingroup$ Higher end will be Planck frequency, lower end - Hubble sphere,- about $14~Gly$, for the photons emitted in one side of sphere can't reach/be detected on the other side, due to the fact that these places will recede from each other at $c$, so cosmological redshift will be infinite. $\endgroup$– Agnius VasiliauskasCommented May 16, 2022 at 8:34
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1 Answer
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In theory, the electromagnetic spectrum should extend indefinitely without limit.
You can create an electromagnetic wave with arbitrarily long or short wavelength, and therefore arbitrarily low or high frequency respectively, by accelerating a charged particle back and forth.
Of course the amount of energy required to accelerate a charge back and forth with any extremely high frequency will be limited to how much energy you have available. So with that, the upper bound of the electromagnetic spectrum will be limited to your supply of energy. That being said, the frequency corresponding to the total energy in the universe may be the true upper bound, in principle.
As for the other extreme, in principle, a vanishingly low enough energy such that the wavelength would perhaps be bounded by the Hubble sphere.
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