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Author Topic: Can visible light generate charged particles in empty space?  (Read 4615 times)

Offline Atomic-S

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Quantum theory indicates that empty space is the site of uncertainty activity, consisting in the spontaneous generation of charged pairs of particles and antiparticles and their subsequent annihilation, all of which is not ordinarily visible. However, if a very strong electric field exists, when particle-antiparticle pairs spontaneously generate, they should be separable and detectable.  The field would separate them before they had a chance to annihilate. Such a field may be providable by a laser that is very powerful and focused to a very tiny spot in empty space. If this is true, it should be possible to focus laser light between charged plates in a vacuum and generate an electric current, due to electron-positron pairs (or some other pairs) being ripped out of empty space between the place, and sent to the plates.


 

Online alancalverd

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Visible photons have energy of the order of 2 - 3 eV. The electron mass is 511,000 eV, so you are a few orders of magnitude short on photon energy. Ther are various means of frequency-doubling a laser output, but the practicalities of doing this a thousand times seem remote.
 

Offline lightarrow

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Alan, your consideration is right, but the OP wrote something different, he wrote about electric field only, which in theory could be possible even with visible light, with a strong enough intensity of the beam, but I don't know how much this field should be.

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Offline lightarrow

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Quantum theory indicates that empty space is the site of uncertainty activity, consisting in the spontaneous generation of charged pairs of particles and antiparticles and their subsequent annihilation, all of which is not ordinarily visible. However, if a very strong electric field exists, when particle-antiparticle pairs spontaneously generate, they should be separable and detectable.  The field would separate them before they had a chance to annihilate. Such a field may be providable by a laser that is very powerful and focused to a very tiny spot in empty space.
Do you have any link about this process, Atomic-S?
 

Offline JohnDuffield

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Quantum theory indicates that empty space is the site of uncertainty activity, consisting in the spontaneous generation of charged pairs of particles and antiparticles and their subsequent annihilation...
I'm afraid it isn't true. There are vacuum fluctuations in empty space, but these aren't charged particles. They're more like photons, and transient ephemeral weak little photons at that. Have you ever been on a ship? Think of a real photon as an oceanic swell wave that barrels across the sea. Think of vacuum fluctuations as the little ripplets on the surface of the sea. 
 

Offline Atomic-S

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According to the following reference:

http://abyss.uoregon.edu/~js/ast123/lectures/lec17.html

the spontaneous generation and annihilation of electron-positron pairs is thought to be a feature of the quantum radiation field, otherwise known as vacuum energy.
 

Offline JohnDuffield

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It just isn't true. Note that in the article you linked to, we can read this:

"Before black holes were discovered it was know that the collision of two photons can cause pair production."

That's fine. That's called gamma-gamma physics, or two-photon physics. The electron and the positron are created from two photons. But they aren't created out of nothing in some spontaneous fashion like worms from mud. Empty space is not some seething mess of electrons and positrons popping in an out of existence. Have a look at Matt Strassler's article  where you can read this:

"The best way to approach this concept, I believe, is to forget you ever saw the word “particle” in the term. A virtual particle is not a particle at all. It refers precisely to a disturbance in a field that is not a particle."

You could say a vacuum fluctuation is a virtual photon, and that you can make a virtual electron and a virtual positron from two virtual photons, but a virtual photon is not a photon, and a virtual electron is not an electron. I'm sorry it's confusing. I don't like the way it's taught. I think it's best to say virtual particles are field quanta. Like you divide a field up into little squares and say each one is a virtual particle. They're something like the "accounting units" of QED. But they aren't short-lived real particles popping in and out of existence.   
 

Offline PmbPhy

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Quote from: JohnDuffield
I'm afraid it isn't true. There are vacuum fluctuations in empty space, but these aren't charged particles. They're more like photons, and transient ephemeral weak little photons at that. Have you ever been on a ship? Think of a real photon as an oceanic swell wave that barrels across the sea. Think of vacuum fluctuations as the little ripplets on the surface of the sea.
I disagree. Vacuum energy consists of Vacuum polarization, i.e. particle-antiparticle pairs such as electron and positrons. The pairs annihilate each other and that's why they're virtual, they don't exist long enough to be detected. If they were photons then photons can't annihilate each other.

You can learn all about this in The Road to Reality by Roger Penrose, (2004), page 676.
« Last Edit: 23/10/2014 11:37:51 by evan_au »
 

Offline JohnDuffield

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Vacuum energy consists of Vacuum polarization, i.e. particle-antiparticle pairs such as electron and positrons. The pairs annihilate each other and that's why they're virtual, they don't exist long enough to be detected. If they were photons then photons can't annihilate each other. You can learn all about this in The Road to Reality by Roger Penrose, (2004), page 676.
All: Space is not full of electrons and positrons popping in and out of existence which "don't exist long enough to be detected". See above, read Matt Strassler's article, and be cautious about what you read in a popscience book. Note though that you can view Penrose's book on  Amazon and search on "virtual electron" to view page 676.
« Last Edit: 23/10/2014 11:40:09 by evan_au »
 

Offline jeffreyH

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Quote from: JohnDuffield
I'm afraid it isn't true. There are vacuum fluctuations in empty space, but these aren't charged particles. They're more like photons, and transient ephemeral weak little photons at that. Have you ever been on a ship? Think of a real photon as an oceanic swell wave that barrels across the sea. Think of vacuum fluctuations as the little ripplets on the surface of the sea.
I disagree. Vacuum energy consists of Vacuum polarization, i.e. particle-antiparticle pairs such as electron and positrons. The pairs annihilate each other and that's why they're virtual, they don't exist long enough to be detected. If they were photons then photons can't annihilate each other.

You can learn all about this in The Road to Reality by Roger Penrose, (2004), page 676.

Hi Pete. This is a very interesting area and one I have not looked into that much. I may well buy the Penrose book when I have the time to read it. At the moment I am looking into energy as it relates to gravitation. I am finding some interesting connections which may be pertinent to the vacuum energy and how gravitation operates in the far field.
 

Offline PmbPhy

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Quote from: jeffreyH
Hi Pete. This is a very interesting area and one I have not looked into that much. I may well buy the Penrose book when I have the time to read it. At the moment I am looking into energy as it relates to gravitation. I am finding some interesting connections which may be pertinent to the vacuum energy and how gravitation operates in the far field.
You don't have to buy it my friend. You can just download it at http://bookzz.org/book/449097/7bf9bf

The direct link is here http://bookzz.org/dl/449097/ba72fd

Quote from: JohnDuffield
All: Space is not full of electrons and positrons popping in and out of existence which "don't exist long enough to be detected". See above, read Matt Strassler's article, and be cautious about what you read in a popscience book.
Take if from someone who knows this stuff. Even in an otherwise perfect vacuum there are virtual particles popping into and out of existence. Those particles include charged particles. See :
http://www.scientificamerican.com/article/are-virtual-particles-rea/

Let me guess. Now it's Scientific American who's wrong, right? Lol!!

Quote from: JohnDuffield
Note though that you can view Penrose's book on  Amazon and search on "virtual electron" to view page 676.
Penrose is talking about vacuum polarization, not vacuum fluctuations. However there are similarities.

However that doesn't really matter because what follows is a highly authoritative source. From The Inflationary Universe by Alan H. Guth, page 272
Quote
According to quantum theory, the apparently quiescent vacuum is not really empty at all, but on the subatomic level is a perpetual tempest, seething with activity. For example, it is possible for an electron and its antiparticle, the positron, to materialize from the vacuum, exist for a brief time, and then disappear back into nothingness. Such vacuum fluctuations cannot be observed directly, as they typically last for only about 10-21 seconds, and the separation between the electron and positron is typically no larger than 10-10 centimeters.
I rest my case.
« Last Edit: 24/10/2014 22:07:54 by evan_au »
 

Offline JohnDuffield

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Take if from someone who knows this stuff. Even in an otherwise perfect vacuum there are virtual particles popping into and out of existence. Those particles include charged particles. See: http://www.scientificamerican.com/article/are-virtual-particles-rea/

Let me guess. Now it's Scientific American who's wrong, right? Lol!!
Yes it is. Here's an excerpt from the article:

"In a hydrogen atom an electron and a proton are bound together by photons (the quanta of the electromagnetic field). Every photon will spend some time as a virtual electron plus its antiparticle, the virtual positron, since this is allowed by quantum mechanics as described above."

This is garbage. Hydrogen atoms don't twinkle, they are not awash with electrons and positrons or throwing out 511keV gamma photons. Virtual particles are merely a mathematical bookkeeping device for quantum mechanics. And they aren't the same thing as vacuum fluctuations. Electromagnetic attraction is nothing at all like the Casimir effect, electrons and protons don't literally throw photons at one another. The notion that they do is popscience pseudoscience for kids.     

 

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