B Can EM Radiations Exist without a Source?

[Rev. Cheeseman]

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?

 

[sophiecentaur]

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.

 

[Haorong Wu]

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?

 

[Rev. Cheeseman]

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?

 

[Dale]

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.

 

[Baluncore]

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?

 

[Rev. Cheeseman]

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?

 

[Rev. Cheeseman]

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?

 

[Dale]

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.

 

[Rev. Cheeseman]

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?

 

[hutchphd]

If you are going somewhere with this, please tell us the destination and we can all enjoy the trip...

 

[Rev. Cheeseman]

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...?

 

[Dale]

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.

 

[hutchphd]

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.

 

[Rev. Cheeseman]

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.

 

[sophiecentaur]

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.

 

[Rev. Cheeseman]

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.

 

[sophiecentaur]

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.

 

[Rev. Cheeseman]

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.

 

[DennisN]

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).

 

[bob012345]

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.

 

[Dale]

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.

 

[phinds]

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.

 

[hutchphd]

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

 

[Vanadium 50]

I disagree that these are "sourceless".

And I disagree that it's "light".

 

[bob012345]

And I disagree that it's "light".

The OP actually mentions light or any EM radiation... I used the word lightly. But I think the virtual photons would include optical frequencies.

https://arxiv.org/pdf/0804.2554.pdf

 

[bob012345]

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

Of course the Casimir effect and the van der Waals force requires matter. But the matter is not the source of the virtual photons which exist independently as I understand it.

 

[Rev. Cheeseman]

Interesting to know that particles can appear out of absolute nothing, such as vacuum fluctuations. Are there any experiments out there that already demonstrated these phenomena?

 

[PeroK]

Interesting to know that particles can appear out of absolute nothing, such as vacuum fluctuations. Are there any experiments out there that already demonstrated these phenomena?

There are several insights articles on the common misconceptions of virtual particles.

In a nutshell, they are a calculation device and not real particles that could be detected.

 

[Rev. Cheeseman]

There are several insights articles on the common misconceptions of virtual particles.

In a nutshell, they are a calculation device and not real particles that could be detected.

So, objects appear out of nothing never actually happened in reality at all even in physics? Then, what is actually happened when vacuum fluctuations happen?

 

[PeroK]

So, objects appear out of nothing never actually happened in reality at all even in physics? Then, what is actually happened when vacuum fluctuations happen?

Read the Insights article(s) on vacuum fluctuations.

 

[Rev. Cheeseman]

Read the Insights article(s) on vacuum fluctuations.

Any links?

 

[weirdoguy]

Here are the links:

https://www.physicsforums.com/insights/vacuum-fluctuation-myth/
https://www.physicsforums.com/insights/misconceptions-virtual-particles/
https://www.physicsforums.com/insights/physics-virtual-particles/

 

[Haorong Wu]

Read the Insights article(s) on vacuum fluctuations.

Wow, great. There is a lot to read and it will take some time. But I am just curious, what really happens in the process such as in Feynman diagrams? Is the answer is that we know how physically describe the whole process, and we build mathematical tools to calculate it but we do not know its true nature?

 

[weirdoguy]

what really happens in the process such as in Feynman diagrams?

We don't know. With every process there are associated infinitely many diagrams, and that thing alone makes it clear (for me at least) that Feynman diagrams are not representations of "what really happens". All we know is that we prepare particles in certain states (in-states), we collide them, and measure what comes out (out-states). We don't know happens during the collision.

 

[PeroK]

Wow, great. There is a lot to read and it will take some time. But I am just curious, what really happens in the process such as in Feynman diagrams? Is the answer is that we know how physically describe the whole process, and we build mathematical tools to calculate it but we do not know its true nature?

In physics generally there is no "true nature". We know what elementary processes take place: scattering, pair production etc. And we can experimentally measure their likelihood. Unless we find a way to probe deeper experimentally, then that is all we can say "really" happens.

We then construct a theory to model what we observe. This is modern particle physics, QFT etc. This theory produces complex integrals that can be expanded as a series of ever more complex terms.

In order to evaluate those terms Feynman invented a system of diagrams, essentially to make the calculations less difficult. One interpretation of those diagrams involves virtual particles.

Whether the model of virtual particle interactions is the "true nature" or only an aid to calculation is not a question physics can answer.

The Insights articles expand on this.

Personally, I believe we should remain agnostic about anything that is beyond our current ability to measure. And focus on what physics can tell us, rather than on what it can't.

 

[Rev. Cheeseman]

I actually hoping for non-mathematical explanations (since my blob inside the cranium can't understand overcomplicated mathematical descriptions) why vacuum fluctuations never actually happened in reality, but after reading Arnold's articles, I think that's what he actually meant. So, if I have to conclude, creation out of nothing such as particles popping out of nothing and vice versa never happened thus everything have existing sources in order to exist. Also, that also means before Big Bang there is no such thing as absolute nothing like what pop-sci said. There could be electrons and quarks, etc. before Big Bang.

 

[bob012345]

I actually hoping for non-mathematical explanations (since my blob inside the cranium can't understand overcomplicated mathematical descriptions) why vacuum fluctuations never actually happened in reality, but after reading Arnold's articles, I think that's what he actually meant. So, if I have to conclude, creation out of nothing such as particles popping out of nothing and vice versa never happened thus everything have existing sources in order to exist. Also, that also means before Big Bang there is no such thing as absolute nothing like what pop-sci said. There could be electrons and quarks, etc. before Big Bang.

I wonder about the views expressed in these Insight articles by Arnold if it is basically the only view among the experts or are there others? It seems to suggest all these mathematical processes that appear like virtual processes are merely calculation tools to get the right answers because you don't know which physical process will happen so you sum up probabilities of various possibilities. If I understand it, QFT gives the average probability amplitude of going from one state to another over an infinite number of trials.

It also suggests that examples such as the Casimir effect and van der Waals forces are only due to the materials involves such as the plates for the Casimir effect and atoms and molecules for the van der Waals forces and nothing else. For example, if there are no vacuum fluctuations involved in the Casimir effect, it should be explainable solely on the grounds of interactions between the atoms of the plates and not on the bases of supposed excluded wavelengths of virtual EM radiation between the plates.

 

[weirdoguy]

if there are no vacuum fluctuations involved in the Casimir effect, it should be explainable solely on the grounds of interactions between the atoms of the plates and not on the bases of supposed excluded wavelengths of virtual EM radiation between the plates.

And it is.

It seems to suggest all these mathematical processes that appear like virtual processes are merely calculation tools to get the right answers because you don't know which physical process will happen so you sum up probabilities of various possibilities.

Yes to the bolded part, but it's not that we don't know which of the processes depicted by Feynman diagrams will happen - we simply do not know what is happening during the "collision". We know only in and out states. I don't know if I recall correctly, but Feynman diagrams were invented a posteriori, after perturbation series was considered. Feynman diagrams are also used outside of QFT , in pure mathematical context of Greens functions and perturbation theory (@Orodruin wrote about it in his book).

 

[bob012345]

And it is.

How is the Casimir effect explained without resorting to certain wavelengths of EM radiation not being allowed between the plates and there being a higher radiation pressure outside the plates? Can you provide a reference? Thanks.

 

[weirdoguy]

First paper that comes to my mind is the one by @Demystifier:
https://arxiv.org/abs/1702.03291
Well, actually it's second, because with the first one I don't remeber authors name, and I can't find it on my computer
Also, calculating the Casimir force is one of the exercises in Radovanović's Problem book in QFT and solution given by him is not reffering to virtual particles, or anything like that.

This issue has been discussed here on PF quite a number of times, so you can search for some threads about that too.

 

[Vanadium 50]

But I think the virtual photons would include optical frequencies.

Virtual photons don't have frequencies.

Do you think this is clarifying things for the OP?

 

[Vanadium 50]

Can you provide a reference?

Bon Jaffe, https://arxiv.org/abs/hep-th/0503158

 

[bob012345]

Bon Jaffe, https://arxiv.org/abs/hep-th/0503158

Thanks. This is a more convincing reference.

 

[hutchphd]

How is the Casimir effect explained without resorting to certain wavelengths of EM radiation not being allowed between the plates and there being a higher radiation pressure outside the plates?

I take issue with your logic here. Even if true, the fact that a particular somewhat obscure result has not been explained without a particular calculational artifice offers scant evidence in support of the larger question.

 

[bob012345]

I take issue with your logic here. Even if true, the fact that a particular somewhat obscure result has not been explained without a particular calculational artifice offers scant evidence in support of the larger question.

The Casimir effect has been studied for decades and is not really some obscure result. I have not seen it described without mentioning vacuum fluctuations. Now, here, people are saying it has nothing to do with the vacuum. So that was my question, what does it have to do with, not how can it not be vacuum fluctuations.

 

[bob012345]

Virtual photons don't have frequencies.

Do you think this is clarifying things for the OP?

If you want to move the Casimir discussion to a new thread or just not discuss it further in this one that is fine with me. I think the original OP question has been answered .

 

[sophiecentaur]

One photon of a frequency is indistinguishable from a photon of the same frequency. Would there be any reason for wanting to identify where a photon came from - except when explaining 'unexplained' photons? That would have to be at the sharp end of experimental Physics when chasing some genuine anomalous results.

I have to question the reasoning behind many of these sorts of threads. They seem to be chasing something 'extra' before getting familiar with what's already been established. Sherlock Holmes got it right about first examining and rejecting all possibilities before considering something apparently impossible.

 

[hutchphd]

some obscure result.

Please quote me correctly. I said "somewhat obscure result". Apology accepted.

 

[bob012345]

Please quote me correctly. I said "somewhat obscure result". Apology accepted.

Retrocausal apology given.