I Can the wavelength of an EM wave exceed the size of the observable universe?

[nmz]

TL;DR Summary

The maximum length of electromagnetic waves depends on the size of the universe. If the universe is infinite, does it mean that electromagnetic waves have no limit?

Some documents show that electromagnetic waves have no limit in theory, but the size of the universe limits the lower limit of wavelength, but I don't know whether it refers to the observable universe or the whole universe, because the observable universe is only a small part of the whole universe, so when electromagnetic waves reach the length of the observable universe, can they continue to grow longerelongate?If not, please point out my mistake.

 

[Dale]

How would you measure the difference?

 

[Ibix]

It kind of depends how far from reality you want to wander.

In an infinite universe you could write down the maths for an arbitrarily long wavelength wave. However, if you want a wave emitted from a source then the wavelength can't exceed the radius of the observable universe, because there hasn't been time to produce a longer one. But the scale of the emitter needed is comparable to the wavelength, so there's a much, much, much lower limit imposed by preparing that. And then there's actual practical emitters, far, far smaller than that.

 

[PeroK]

TL;DR Summary: The maximum length of electromagnetic waves depends on the size of the universe. If the universe is infinite, does it mean that electromagnetic waves have no limit?

Some documents show that electromagnetic waves have no limit in theory, but the size of the universe limits the lower limit of wavelength, but I don't know whether it refers to the observable universe or the whole universe, because the observable universe is only a small part of the whole universe, so when electromagnetic waves reach the length of the observable universe, can they continue to grow longerelongate?If not, please point out my mistake.

An EM wave is a mathematical construction. It's not a physical object. In any case, to generate something with so little energy would probably take you into the realm of Quantum Field Theory, rather than classical optics.

 

[nmz]

It kind of depends how far from reality you want to wander.

In an infinite universe you could write down the maths for an arbitrarily long wavelength wave. However, if you want a wave emitted from a source then the wavelength can't exceed the radius of the observable universe, because there hasn't been time to produce a longer one. But the scale of the emitter needed is comparable to the wavelength, so there's a much, much, much lower limit imposed by preparing that. And then there's actual practical emitters, far, far smaller than that.

Since the wavelength of electromagnetic wave can theoretically exceed the observable universe, can it reach the size of the whole universe?

 

[Ibix]

Since the wavelength of electromagnetic wave can theoretically exceed the observable universe, can it reach the size of the whole universe?

An infinite wavelength wave makes no sense - any pair of finitely separated points must have the same phase. So if the universe is infinite in size you can write the maths for an arbitrarily long wave, but not an infinitely long one.

I think this is pretty far across even the fuzziest of lines between physics and navel gazing, though. There's no way to do this even in principle, there's no way to test it even in principle, is it really physics?

 

[snorkack]

In classical physics, the frequency of wave is unconnected to its energy. In quantum physics, it sets only the lower bound for energy, and that only for some purposes.
Electromagnetic wave with wavelength far bigger than universe would look like magnetostatic and electrostatic fields that exist across the observable universe.
Since universe is largely ionized and thus conductive of electricity, electromagnetic waves and electrostatic fields would tend to induce electric currents and thus be hampered. Magnetostatic fields are not so hampered.
We are looking for dipole and quadrupole asymmetries of relic radiation and of galaxies. After the dipole asymmetry due to peculiar motion of milky way, several searches find low quadrupole anomalies, and relic radiation patters at smaller scales than whole universe. But some surveys do claim excessively large structures.
If observable universe had a small violation of isotropy due to a modest magnetostatic field in a specified direction, how would it affect the observable relic radiation? How about galaxies?

 

[weirdoguy]

In classical physics, the frequency of wave is unconnected to its energy.

Which, by the way, is not true for mechanical waves. I know the context of this thread, but if someone read it out of context...

 

[Dale]

Since the wavelength of electromagnetic wave can theoretically exceed the observable universe, can it reach the size of the whole universe?

Again, how could you measure the difference? I would like you to actually answer this question.

 

[sophiecentaur]

TL;DR Summary: The maximum length of electromagnetic waves depends on the size of the universe. If the universe is infinite, does it mean that electromagnetic waves have no limit?

Some documents show that electromagnetic waves have no limit in theory, but the size of the universe limits the lower limit of wavelength,

I think you mean 'upper limit'?
There can be confusion about how much room a standing wave can take up and the possible wavelength of a travelling wave. As an example, the wavelength of 50Hz mains electricity is 6000km (ish) but the stuff gets around our homes and we hear 'mains hum' everywhere.

An upper limit is all about the maximum possible Energy. The Energy limit to EM waves that 'we' can produce will be probably what the CERN machine can manage (6.5 TeV) but there are more extreme conditions out there; not a matter of geometry though.

 

[snorkack]

An upper limit is all about the maximum possible Energy. The Energy limit to EM waves that 'we' can produce will be probably what the CERN machine can manage (6.5 TeV) but there are more extreme conditions out there; not a matter of geometry though.

We can observe high energy photons in cosmic rays. For these, however, Breit-Wheeler process makes light absorb light at high energies, such that the higher energy photons can be seen only from nearby sources.

 

[Hop-AC8NS]

I sometimes have enjoyed navel gazing, not so much since quitting drinking in the late 1980s. Is this thread going anywhere? As the Man said: How would you measure it? My personal opinions are influenced by observable facts, but they are still just opinions, not necessarily science. I guess humans will have to wait until we die to possibly discover certain things. Or not. May you all live interesting lives in the meantime. Peace is my profession.

 

[sophiecentaur]

How would you measure it?

Good question. The equipment would need to run for billions of years to detect such a 'low frequency'. We could be too late already.

 

[snorkack]

Good question. The equipment would need to run for billions of years to detect such a 'low frequency'. We could be too late already.

A section of a low frequency electromagnetic wave is inter alia magnetostatic field.
Do we know the direction of magnetostatic field in intergalactic space?

 

[sophiecentaur]

Do we know the direction of magnetostatic field in intergalactic space?

Not in the few years we've been able to measure it. We would need to detect a time derivative of the field with a 'real' infinitessimals almost.

 

[hutchphd]

I sometimes have enjoyed navel gazing

It is more enjoyable if you call it omphaloskepsis. (This revelation engendered by years of intense medication meditation)

 

[phinds]

It is more enjoyable if you call it omphaloskepsis. (This revelation engendered by years of intense medication meditation)

This post really requires two response icons from me. Informative and humorous.

 

[sophiecentaur]

I sometimes have enjoyed navel gazing,

Watching those warships going in and out of Portsmouth Harbour at the same time? (Apologies.)