Have you ever thought about what "nothing" truly is? We used to think about it in terms of simply removing all the particles from a given region of space, which is a pretty intuitive definition of nothing. But quantum physics is notorious for defying our intuition.
Public domain image.
When we take a look at this "empty" space, we find it's not so empty at all. Not in terms of energy, and not -- if we consider that particles are not just real but also virtual -- in terms of what's physically inside.
Image credit: Derek Leinweber.
If you've ever wondered about "nothing," take a trip with Sabine Hossenfelder to the edge of the quantum and cosmic seashore, where she explores all this and more!
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Virtual particles aren't short-lived real particles that pop in and out of existence. That's just a popscience myth for kids. See Matt Strassler talking about them. They're the "field quanta" of quantum electrodynamics. It's like you divvy up the field into little chunks and say each is a virtual particle. Then an electron and a proton attracting one another will effectively "exchange field" such that the hydrogen atom has little field remaining. Thereafter two hydrogen atoms attracted gravitationally don't "exchange field", so we don't have quantum gravity.
Also note that virtual particles aren't the same thing as vacuum fluctuations. See this old paper which says "the identity of these evanescent waves with virtual photons is established". The evanescent wave is also known as the near field. It's a standing field. Neither it nor space is a seething mass of electrons and positrons being created spontaneously like worms from mud.
Boo! Hiss! The vacuum is not nothing. No thing is nothing. If nothing were the vacuum, then it would be something. To be is to be something. This is basic Aristotle, not to mention common sense.
I am disappointed, you are usually on the right side of both physics and metaphysics.
@John Duffield, I did not get the impression that the author was claiming that virtual particles are short-lived real particles that pop in and out of existence. The article states: "[The vacuum is] full with virtual particles that constantly bubble in and out of existence."
Your note about photons and the near field is interesting. In my understanding of radio wave propagation, the near field around the transmitting antenna does not contain electromagnetic waves per se, it takes a distance of several wavelengths for the self-propagating electromagnetic wave to become established -- these self-propagating waves are the real, radiated, far-field photons. I have no idea if virtual photons exist in the near- to mid-field region.
@Pete A : I've just had another look, and the author says "virtual particles can only be created together with their anti-particles" and "the virtual particle pairs can only exist for a short time, and the more energy they carry, the shorter the duration of their existence". This just isn't true. Virtual particles aren't short-lived real particles. There are no genuine electrons and positrons popping in and out of existence like magic. QED is modelled using virtual particles, but they're "chunks of the field", that's all. I don't know where this popscience myth has come from that virtual particles are short-lived real particles. But it's got legs.
Note that there's a mention of virtual photons in the Wikipedia near and far field article. But also note that the near field or evanescent wave is a standing wave. It's static. It's just a standing field, not some seething mass of particles that we can't actually see.
Interesting article. A bit over my head. But I try. So the vacuum of space is not empty after all. Imagine that. Every time you think you know something about the universe it throws a curve ball.
I wish I had a starship and the ability to sail to the stars.
@John #4: Thanks for the explanations and the Wiki link.
I knew that the near field of an antenna contains standing waves, similarly in acoustics, but it had never occurred to me that it applies to quantum mechanics (other than just photons and phonons).
@4 and @5: could the problem be that the author got on a 'virtual' writing roll and included an extra "virtual" where they shouldn't? I'm thinking specifically of this paragraph:
Photons, the quanta of light, are electrically neutral and do not interact with each other. This is why light of different colors adds without distortion. But a photon can decay into a virtual pair of an electron and its anti-particle...
Photons above 1.022 MeV do not decay into virtual particles, they decay into real ones that can be detected with positron/electron detectors and even gamma detectors as the broadening of the 511 keV peak. I suspect this is not necessarily what the author is talking about, but it would be easy for someone to read the above and think the author was referring to the production of real particle pairs from high energy photons.
oops, wierd html flub. Sorry about that. The misplaced line is mine and should not be in italics.
@6: I must admit that I didn't understand "...a photon can decay into a virtual pair...".
I've now read the article for a fifth time and I still don't get the impression that the author is in any way suggesting that virtual particles are real particles. It's very clear to me that the article is suggesting that virtual particles are like waves that bubble in and out of existence. And at the end of the article: "Now what exactly it means for mathematics to 'exist' I better leave to philosophers."
As Wikipedia states:
"In physics, a virtual particle is an explanatory conceptual entity that is found in mathematical calculations about quantum field theory."
And it goes on to state (with which I agree):
"Note that it is common to find physicists who believe that, because of its intrinsically perturbative character, the concept of virtual particles is a frequently confusing and misleading one, and is thus best to be avoided."
http://en.wikipedia.org/wiki/Virtual_particle
How come a new comment has been inserted at #5? My last reply was to eric not myself :-)
Pete: it will be because the comment was awaiting moderation. As regards the article is suggesting that virtual particles are like waves that bubble in and out of existence, that's vacuum fluctuations. Virtual particles aren't the same thing. They're just conceptual things in mathematical calculations. Remember this: hydrogen atoms don't twinkle, and magnets don't shine.
Eric: it's a cargo-cult myth that photons don't interact with one another. See two-photon physics on Wikipedia where the myth is repeated: "From quantum electrodynamics it can be found that photons cannot couple directly to each other, since they carry no charge, but they can interact through higher-order processes. A photon can, within the bounds of the uncertainty principle, fluctuate into a charged fermion–antifermion pair, to either of which the other photon can couple". It's a popscience tautology. A 511keV photon does not spend its life morphing into a 511keV electron and a 511keV positron which then magically morph back into a single 511keV photon which manages to keep on moving at c. Pair production does not occur because pair production occurred! Photons interact with photons, but they have to be high-energy photons. See the Breit-Wheeler process.
For a different opinion on virtual particles, see this (the top match for my Google search just now):
http://www.scientificamerican.com/article/are-virtual-particles-rea/
This sounds like one of those open-ended philosophical questions to me. (And if a tree falls in the forest and I'm not there, I don't give a frack whether or not it makes a sound.)
John Duffield:
Of course it doesn't, that would violate conservation of energy. Of course, that's also not what I said. I also never said photons don't interact with each other; I didn't say anything about photon-photon interactions at all. And the Breit-Wheeler process is a two-photon process, that's also not what I'm talking about. So...you're batting 0 for 3.
JD is consistent that way.
I think that the word "virtual" is now so overloaded with multiple meanings that it has become meaningless. E.g. I use a virtual machine application that is real: it allows me to run multiple operating systems. But if I was asked to put my money into a virtual bank account I would assume it to be a scam — as ridiculous as claiming that buying a lottery ticket is a sound virtual investment.
If as John has stated (and my quote from Wikipedia seems to confirm) that virtual particles are just conceptual things in mathematical calculations, then why aren't they called abstract X, or just X, where X is a uniquely-defined name rather than using the word "particle"?
I really enjoy science and I'm a stalwart supporter of using evidence combined with the scientific method, however, I find some of the terminology in certain branches of science to be so embarrassingly inept that they have become self-ridiculing rather than self-explanatory. I.e. rather than having explanatory power, the terms have only the power to confuse and divide both scientists and the general public.
The term "photon" is an example of a really good term because people either know what it means or they can easily find out what it means. "Virtual particle" is a terrible term because people can spend many hours, days, months, performing Web searches then end up being hopelessly misguided through no fault of their own.
"When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean — neither more nor less." — Lewis Carroll.
Humpty Dumpty science is arrogance personified: a totally unnecessary appeal to authority that masks the profound levels of expertise and solid evidence that goes into painstaking scientific discoveries.
Its true that there are a number of naming conventions in science that owe more to historical accident than rational analysis. However, in some cases terms that seem inept because they are wrong in principle make sense because they are useful in practice. For example, a phonon is not a real particle, but treating the system (compression waves moving through a solide) as if such particles exist make it easier to accurately model its behavior. I'm guessing the term 'virtual particle' arose out of a similar circumstance: physics find some phenomena. That phenomena is accurately modeled by treating it as if it had particle-like properties. So they call it a virtual particle.
As for the semantic confusion arising from the other ways we now use the term "virtual"...I think you're putting the cart before the horse there. You can't blame 1930s physicists for making up with a term that is confused with the 1980s computer science usage of the same term. If you're going to blame anyone for that confusion, the only rational choice is to blame the computer scientists for adopting a term already in use for something else. :)
My work was always in the application of multiple branches of science, rather than in science itself, so I've never considered the etymology of scientific words and terms. Just like a non-scientific layperson, I learnt the meanings of words and terms as I encountered them rather than in their correct chronological order.
The dictionary supplied with my computer has five definitions for the word virtual, here's an extract:
virtual [adjective]
1 almost or nearly as described, but not completely or according to strict definition.
2 Computing: not physically existing as such but made by software to appear to do so.
…
5 Physics: denoting particles or interactions with extremely short lifetimes and (owing to the uncertainty principle) indefinitely great energies, postulated as intermediates in some processes.
To a layperson, item 5 is gobbledegook and a profound example of "Humpty Dumpty science".
Promoters of science, including myself, have to frequently point out that a scientific theory is a currently established fact. E.g. the theory of evolution is not a supposition based on wishful thinking; neither is it a hypothesis waiting to be validated. The other thing that needs to be constantly pointed out is that science is self-correcting, which makes it the most reliable source of knowledge and discovery about reality that we currently possess. This was all superbly illustrated by the late Carl Sagan in his book The Demon-Haunted World: Science as a Candle in the Dark.
Unfortunately, it seems that many scientists have not bothered to read Sagan's book, or if they have, they refuse to heed his warnings. "String theory" is one obvious example of word bastardization: it should've been named "string hypothesis" because it is not an established fact; it has far too many eminent critics to boldly claim itself to be a scientific theory. The multiverse hypothesis is another example of science embarrassing itself: is it a testable hypothesis? No! Even the forthcoming James Webb Space Telescope will not be able to observe another universe.
It's difficult enough to promote science as our only candle in the huge expanse of darkness. The last thing we need is branches of science that do little more than to mock the promoters of science, other branches of science, and those who've dedicated themselves to real-world applications of science, such as the fields of 21st century medicine and engineering.
@Eric re #13@ sorry, I was just correcting something that you quoted from the article in comment #7. There's this myth that photons don't interact with photons. It isn't true. Gamma-gamma pair production doesn't occur because one of the photons magically turns into an electron-positron pair. Spontaneously. Like worms from mud. It occurs because the photons interact with each other.
Hi John,
There’s some interesting stuff in this thread. The thing that surprises me is that anyone could interpret the author of the article as saying that virtual particles are short lived real particles. I suppose it’s all a matter of how one sees it.
You have undoubtedly seen me complain elsewhere that we seem to have reached a point where we have to use “absolutely nothing” when we mean “nothing”. I feel sure the author is aware of this shift, but does nothing to stem the tide.
I, too, like Mat Strassler’s treatment of virtual particles, I found it very helpful.
One thing I was not so happy about was:
“On the seashore, you now have to wade through the water, which will slow you down. This is what the Higgs field does: It drags down particles and thereby effectively gives them mass.”
This might tend to perpetuate the belief that it is motion through the Higgs field that gives mass.
John Duffield:
Well, now you're wrong again. A 1.022 MeV photon can spontaneously convert in to a positron-electron pair in the presence of an atom (not a second photon). This pair can then annihilate to form a pair of 511 keV photons. A second photon is not needed for pair production.
I don't know any that do this. And I know a few scientists and some work on testing or proving that theory.
They claim they have a theory.
@Wow: It was named "string theory" therefore a group of people claimed it to be a theory. Whether or not these people were scientists is perhaps debatable.
If scientists are working on testing it then it is not a theory, it is a hypothesis that is awaiting either validation or dismissal.
Yes. They have a theory, String theory, a theory of how it could be that particles are just persistent modal vibrations in some "string like" stuff.
The theory makes predictions which mostly haven't been borne out, but not to such an extent there is nothing left to the theory.
They aren't saying its the theory. Just a theory.
Well, those who thought up the theory and put it into scientific nomenclature for testing were all scientists. Though you can ALWAYS find someone to debate ANYTHING, no matter how dumb it would be to argue against it.
Yes, it's a hypothesis called "String Theory".
Where was your problem again?