Light without a source

  • #1
Can electromagnetic radiations exist on their own without any source (i.e light existing on its own without flashlight). If light can't exist on its own so sources are necessary for light or any EM radiations in order to exist, how about the EM fields?
 

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  • #2
sophiecentaur
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Can electromagnetic radiations exist on their own without any source (i.e light existing on its own without flashlight). If light can't exist on its own so sources are necessary for light or any EM radiations in order to exist, how about the EM fields?
Any light that you 'see' must have come from a source of charges and energy changes. Otoh, I think you could consider the Cosmic Microwave Background Radiation as having been there for the life of the Universe. But even that would have had an origin in the Big Bang so, apart from a chicken and egg situation at the start of things, the answer to your OP is No.
 
  • #3
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Any light that you 'see' must have come from a source of charges and energy changes. Otoh, I think you could consider the Cosmic Microwave Background Radiation as having been there for the life of the Universe. But even that would have had an origin in the Big Bang so, apart from a chicken and egg situation at the start of things, the answer to your OP is No.
Hi, @sophiecentaur. What about the Hawking radiation? A pair of photons are created from vacuum due to vacuum fluctuation, and then one of them falls back to the black hole while the other one escapes. Could that be the light without a source?
 
  • #4
Any light that you 'see' must have come from a source of charges and energy changes. Otoh, I think you could consider the Cosmic Microwave Background Radiation as having been there for the life of the Universe. But even that would have had an origin in the Big Bang so, apart from a chicken and egg situation at the start of things, the answer to your OP is No.

Same goes for any electromagnetic fields too except for the CMBR?
 
  • #5
Dale
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Can electromagnetic radiations exist on their own without any source (i.e light existing on its own without flashlight). If light can't exist on its own so sources are necessary for light or any EM radiations in order to exist, how about the EM fields?
Light can exist without a source. Such situations are called vacuum solutions. The sources of light are charges and currents. So a vacuum solution is one that contains an EM field without any charges or currents.

The light that we see today probably all has a source. Even the CMB has a source, which is called the surface of last scattering. So the idea that light can have no source is mostly theoretical. Meaning it is compatible with known physics but not actually observed.
 
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  • #6
Baluncore
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Since a photon has energy, and travels at the speed of light, the question could be rephrased to,
“must propagating energy have a source”. What gives, can we dismiss conservation of energy?
 
  • #7
Light can exist without a source. Such situations are called vacuum solutions. The sources of light are charges and currents. So a vacuum solution is one that contains an EM field without any charges or currents.

The light that we see today probably all has a source. Even the CMB has a source, which is called the surface of last scattering. So the idea that light can have no source is mostly theoretical. Meaning it is compatible with known physics but not actually observed.
If I understands you correctly, vacuum solutions had never been observed in reality but are just hypothetical then?
 
  • #8
Since a photon has energy, and travels at the speed of light, the question could be rephrased to,
“must propagating energy have a source”. What gives, can we dismiss conservation of energy?
Everything just changing form from another to another, that's understandable. So, every propagating energy have sources then?
 
  • #9
Dale
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If I understands you correctly, vacuum solutions had never been observed in reality but are just hypothetical then?
I think that is a fair assessment. Of course, we don't always know the source of every EM wave we have ever observed, so I would be hesitant to say "never". Certainly we have never determined that an observed EM wave had no source.
 
  • #10
I think that is a fair assessment. Of course, we don't always know the source of every EM wave we have ever observed, so I would be hesitant to say "never". Certainly we have never determined that an observed EM wave had no source.
So, so far, we can safely concluded that every electromagnetic fields have sources in order to exist. But given that atoms are everywhere in the universe, even in the most perfect vacuum, there will be also electromagnetic fields everywhere. Is that correct?
 
  • #11
hutchphd
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If you are going somewhere with this, please tell us the destination and we can all enjoy the trip......
 
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  • #12
If you are going somewhere with this, please tell us the destination and we can all enjoy the trip......
I just want to understand whether EM fields or EM waves, etc. can exist on their own without sources. Sometimes I think some EM fields or EM waves can exist without sources somewhere in the universe including the emptiest parts of universe.

Get it...?
 
  • #13
Dale
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whether EM fields or EM waves, etc. can exist on their own without sources.
This has already been answered. What remains?

In principle/theory, yes they can exist without sources. In practice, they all have sources as far as we know. Just because something can happen doesn’t mean that it does happen.

This has all been stated already.
 
  • #14
hutchphd
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OK. I think every known bit of E M energy in the universe can be traced to a nonzero source. It is not unusual to dismiss allowed solutions because they do not match the boundary conditions.
Whether this source still "exists" is a question fraught with the usual relativistic issues.
 
  • #15
Ok, so the answer remains so far "electromagnetic activities (EM field, EM waves, etc.) can be traced to nonzero sources". Then, everywhere in the universe there are particles and resulting EM fields/waves.
 
  • #16
sophiecentaur
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Get it...?
Hmm. But do you get it?
You don't define what you mean by a source - so there can't be an answer. The only waves that your question could refer to would have had to originate 'before' the Big Bang. These would presumably have to be low frequency (?).
If you want'spontaneous generation' of waves in the context of 'vacuum' then you'd just have to look for evidence. Afaiaa, the jury's still out on that and you should be careful of anything that's published about it without a lot of support from recognised bodies. Only time will tell.
 
  • #17
Hmm. But do you get it?
You don't define what you mean by a source - so there can't be an answer. The only waves that your question could refer to would have had to originate 'before' the Big Bang. These would presumably have to be low frequency (?).
If you want'spontaneous generation' of waves in the context of 'vacuum' then you'd just have to look for evidence. Afaiaa, the jury's still out on that and you should be careful of anything that's published about it without a lot of support from recognised bodies. Only time will tell.
You seems upset. Sorry if I indeed making you upset.

The sources can be anything. Charge, flashlight, etc. But as what you guys already said above, so far EM activities (EM field, EM waves, etc.) must have sources in order to exist at least in reality. But hypothetically, EM activities without source are possible but not observed yet.
 
  • #18
sophiecentaur
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You seems upset.
Nah. Not upset. Just a bit frustrated that you seem to be looking for an answer that's exclusively on your own terms. You will be very lucky if you find that kind of answer.
 
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  • #19
Nah. Not upset. Just a bit frustrated that you seem to be looking for an answer that's exclusively on your own terms. You will be very lucky if you find that kind of answer.
It's okay, so far every answers are useful.
 
  • #20
DennisN
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Can electromagnetic radiations exist on their own without any source (i.e light existing on its own without flashlight). If light can't exist on its own so sources are necessary for light or any EM radiations in order to exist, how about the EM fields?
The sources can be anything. Charge, flashlight, etc.
If by "sources" you mean the object(s) from which the light came, there's nothing that says the "sources" still have to exist for electromagnetic radiation to exist. As an example, if a particle and a corresponding antiparticle get annihilated, they will cease to exist and this process will produce gamma rays. See e.g. Positron Annihilation (HyperPhysics).
 
  • #21
bob012345
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Light can exist without a source. Such situations are called vacuum solutions. The sources of light are charges and currents. So a vacuum solution is one that contains an EM field without any charges or currents.

The light that we see today probably all has a source. Even the CMB has a source, which is called the surface of last scattering. So the idea that light can have no source is mostly theoretical. Meaning it is compatible with known physics but not actually observed.
What about the Casimir effect between two plates? Would that not in effect constitute a direct observation of the reality of 'light without a source' meaning vacuum fluctuations? Also related are van der Waals forces.
 
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  • #22
Dale
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What about the Casimir effect between two plates? Would that not in effect constitute a direct observation of the reality of 'light without a source' meaning vacuum fluctuations? Also related are van der Waals forces.
Well, I think that I would attribute the Casimir force to the plates and the van der Waals force to the molecules. But you do make a good point about the vacuum expectation. I had not considered that above.
 
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  • #23
phinds
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Hi, @sophiecentaur. What about the Hawking radiation? A pair of photons are created from vacuum due to vacuum fluctuation, and then one of them falls back to the black hole while the other one escapes. Could that be the light without a source?
@Haorong Wu The "virtual particle pair" description of Hawking Radiation is not an actual description of what happens. It is a heuristic created by Hawking himself who said that it was the only way he could figure out how to say in the English language what really can only be said in the math.
 
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  • #24
hutchphd
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What about the Casimir effect between two plates? Would that not in effect constitute a direct observation of the reality of 'light without a source' meaning vacuum fluctuations?
I disagree that these are "sourceless". Each requires the presence of matter containing charges and some source of Energy (temperature?) to produce measureable effect I believe. Does not pass the "no source" test in my book
 
  • #25
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I disagree that these are "sourceless".
And I disagree that it's "light".
 
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