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Is There a Limit To a Laser's Energy?
StartsWithABang (3485481) writes "For normal matter — things like protons, neutrons and electrons — there's a fundamental limit to the number of particles you can fit into a given region of space thanks to the Pauli exclusion principle. But photons aren't subject to that limit; in theory, you could cram an infinite number of them into the same exact state. In principle, then, couldn't you create a laser (or lasing cavity) with an infinite amount of energy inside? Perhaps, but there are some big challenges to be overcome!"
It's the number of sharks you can fit into a given region of space.
Eventually the laser energy will create a black hole, provided some other exotic effect doesn't occur first. Realisitcally though it's not possible to attain those kinds of photon densities (nothing can reflect anywhere close to well enough for starters).
Napoleon, like anyone can even know that.
http://www.phy.ilstu.edu/ILP/r...
http://www.phy.ilstu.edu/ILP/r...
Etc...
"Update: After a conversation with Chad Orzel, it looks like although there's no limit to the photon energy you can produce, you will at some point--above about 1 MeV in photon energy--start spontaneously producing matter-antimatter pairs of particles whenever your photon interacts with a reflective surface. So at extremely high photon energies, your laser light begins to resemble a matter-antimatter thermal bath rather than merely coherent light."
So it would act like more Star Wars weapons?
Table-ized A.I.
Billions and billions of years ago, even before lord Xenu, there was a scientist who pulled this off.
Blext Telfrawd, an A type Hixoid, did get an infinite number of protons into a finite space. Then the containment field faltered, obliterating the iteration of his universe..
Most historians agree this was tragic for it ended his universe, and created one with Justin Bieber. Sentients who were able to achieve trans-dimensional universital access, send a message to you from the past: It's just too risky to repeat the so called "Bieber Event",
You've been warned.
Another consultant who stuck it out.
"We are the Priests, of the Temples of Syrinx..."
Okay. Interesting on a theoretical level.
The main problem with testing this is "how does one generate infinite or near-infinite energy" to power something like this?
Of course, if we've answered that, we're ALREADY in a place where we've either wiped ourselves out (accidentally or otherwise), or we've basically solved the greatest real-world problem in the history of humanity.
Chas - The one, the only.
THANK GOD!!!
The power generation isn't one billionth as hard as - how the hell do you get that energy (presumably electrical) to the device in the first place in a usable format? You can alway just build a nuclear fusion plant, then another, then another, then another, then another, in close proximity.
But somewhere, somehow, you have to transport or convert that amount of energy in a non-light way, which is going to involve some humungously gigantic amount of heat on a physical component, or some monstrously huge device to attempt to dissipate the heat.
The problems of generation are solveable - we just need a way to harness something like a Sun (e.g. Dyson spheres). The problem you really have is how do you concentrate that energy onto a point such that it generates a laser?
Two or three of Elon Musk's batteries of sheer awesomeness should do it.
Make it four, in case one catches fire.
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
The energy of a photon is characterized by its wavelength. In a laser, the wavelength is constant. You have a large amount of photons which are coherent but at an almost single wavelength. When the article is talking about 1 MeV, it falsely interprets this as if the laser is emitting a single photon at 1 MeV. That is not what happen. It emits many photons in coherence which the sum of energy of all the individual photons will reach 1 MeV or more. Each photon cannot create an electron-positron pair and all photons collectively cannot create an electron-positron pair.
A 1 MeV photon would be a gamma ray photon and it is not true at all, your laser doesn't change its wavelenght as more more "energy" is emitted. In fact, we should instead talk about the power of the laser rather than its energy. The power being the amount of energy emitted by unit of time.
Achille Talon
Hop!
Yes.
Science is all about firing a drunk pig out of a cannon just to see what happens.
Eventually the laser energy will create a black
hole
There is a specific term in astrophysics for such a theoretical object:
http://en.m.wikipedia.org/wiki...
But long before that happens the question is if the laser can remain a laser.
A laser needs some kind of nonlinearity in the medium. Any nonlinearity introduces a scale. So the real question is: At which power does of-resonant driving cause transitions (e.g. Landau-Zener) or of-resonant shifts (Stark shift) and can you actually theoretically contruct a medium which fulfills the criteria to serve as a lasing medium for an arbitrary large scale of power?
As a starting point for an examination of such questions i recomment the Quantum Optics Toolbox for Matlab by Sze Tan.
There was an article from 2010 that talked about the theoretical limit to laser beam energy. From the article:
"At high laser intensities interaction of the created electron and positron with the laser field can lead to production of multiple new particles and thus to formation of an avalanche-like electromagnetic cascade"
Here's the link to the article in question: http://physicsbuzz.physicscent...
That article was ultimately using this article as a source.
As a certain energy density, the radiation pressure from the photons will be stronger than the tensile strength of the optical cavity, and the laser will blow apart. In astronomy, a similar limit is called the Eddington limit, so this is really the Eddington limit for a laser.
The radiation pressure is (ignoring all factors of 2 or cos(incidence)) E / c. A tensile limit, T, of 500 mega pascals (reasonable for steel) thus would imply an energy intensity of c T, or 1.5 x 10^17 Watts/m^2. If the total cavity had an area of 1 m^2, then that's ~ 10^17 Watts.
Note that it is common in pulsed lasers to have a lot of energy in a very short pulse (so the actual power during the pulse is very high). If your pulses were a microsecond in length, then the Eddington limit per pulse would be about 10^11 Joules, equivalent to 24 tons of TNT.
We can outright throw it out, as there isn't an infinite amount of energy in the visible universe.
I read TFA and all I got was this lousy cookie
At high enough energies particles are spontaneously created. They in turn will obey Pauli Exclusion (at least if they have spin I think). So enough photons and you make matter that will prevent you from making more particles ie pumping more energy into the space.
This effect will not only kill at high energies but at high intensity too. With a high enough intensity you can have multi-photon interactions to achieve the same total energy. However pair production is not the only process you have to worry about compton scattering will occur as well. This will impose an intensity limit well below pair production energies.
Essentially reflected photons will have less energy than incident photons and as the energy increases so too does this energy difference. It is caused by relativistic effects when a photon is reflected from an electron. At visible wavelengths the effect still occurs but is not noticeable but crank the energy up to several keV and your photon has an energy more comparable to the electron rest mass energy and the effect kicks in.
No, it doesn't. In maths, we use the phrase, "finite but unbounded". This describes the natural numbers, for example: each specific integer is strictly finite, but there's no finite upper limit.
Eventually the laser energy will create a black hole, provided some other exotic effect doesn't occur first.
That's a limit on energy density, not total energy in the laser. In principle you could use a very WIDE laser opterating below the black-hole thrshold and focus the beam externally (which, if it's powerful enough, it might do eventually, by self-gravitation, after leaving the cavity, even if the cavity geometry made it emit a colimated, rather than a converging, beam.) Thus, making a kugelblitz with a (very wide) laser might be theoretically possible (if "some other exotic effect" didn't make the required laser cavity to wide to be physically realizable).
I'd imagine "Some other exotic effects" might include the electric field component of the coherent light becoming strong enough to polarize the vacuum and create particle-antiparticle pairs from multiple photons, dissipating their energy, somewhere WAY below the threshold of gravitic-collapse effects. So you'd need a REALLY WIDE laser and REALLY GOOD optics to make your external-to-the-laser black hole.
Of course the question, being phrased in terms of Bose-Einstein vs. Fermi-Dirac statistics and "infinite" energy was really about energy density in the cavity - just poorly phrased. So you answered the question that was REALLY being asked.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
"Physics" is not just one thing anymore. The guy writing TFA, Ethan Siegel, is a bonified professional physicist. Reading the comments, you can see he just didn't know this one thing as well as he thought. How does that happen?
I don't know that there's any physicist going through training today or in the last 20 years who really understands "all" of physics.
Physics PhDs learn most of physics up to about 1910 (even that is a stretch, but at least the complete fields up to that point are introduced and sketched out), and the next 100 years are based on your specialty. The limits of energy density for photons are usually in this realm of "introduced only if directly important to your specialty."
It's up to the individual to fill in the gaps after formal classes, and it can be very hard to figure out what you don't know. It's particularly hard because of the oversimplified way physics is generally taught in undergrad, even to physics majors. Your old reference books may not actually be correct. I'm sure I've got a physics textbook around which claims almost exactly what Ethan said in his blog; the "why" of pair generation is just too distracting.
Bose-Einstein Condensate! In more detail, fermions cannot be crammed together but in certain conditions, Bosons can. Photons are a type of Boson but not the only one. The Pauli exclusion principle does not apply to Bosons! Looks like a non-specialist needs to read some books on this concept. I won't even go into deeper details without this point being crystal clear!