Scientists discover how to turn light into matter after 80-year quest

http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_16-5-2014-15-32-44

by Libertatea • 12 years ago

117 45 12 years ago

www3.imperial.ac.uk

Noxchi• 12 years ago

So it's turning light into electrons? Isn't that already done with solar panels?

pjc502• 12 years ago

No, solar panels turn light into the change of energy state of an existing electron. This is why they operate at the characteristic band gap voltage of the semiconductor from which they are made.

This experiment is about creating an entirely new electron/positron pair.

tannerc• 12 years ago

Solar panels wouldn't be the ideal use of this ability if it were made real, would they? I haven't looked through the full article yet, but would this new approach help overcome the problem of Carnot's theorem in any way?

chris_va• 12 years ago

Solar panels add momentum to existing electrons.

This is actually quite exciting.

Toenex• 12 years ago

I see what you did there.

frozenport• 12 years ago

I'll count my chickens when they hatch, lets wait until they do it.

JacobAldridge• 12 years ago

To be clearer, Theoretical Physicists have a theory about an experiment that would allow Experimental Physicists to prove a theory made by earlier Theoretical Physicists. They haven't actually conducted the Experiment.

"In Theory, there is no difference between Theory and Reality. But in Reality there is."

scott_s• 12 years ago

I prefer the phrasing, The only difference between theory and practice is that in theory, there is no difference between theory and practice.

cLeEOGPw• 12 years ago

Imperial mages learn conjuration.

gregorkas• 12 years ago

1. grab a flashlight 2. make your friend grab a flash light 3. turn them on and point them at each other 4. make it rain

tlholaday• 12 years ago

My friend is so obstinate I cannot complete step 2, and now there is severe drought.

nkozyra• 12 years ago

By no means is this my forte, but would this violate the conservation of mass?

cboursnell• 12 years ago

Nope. As energy equals mass times the speed of light squared you're just converting energy into matter. It's just the opposite of what the atomic bomb does.

asolove• 12 years ago

Conservation of mass is not applicable in the conditions under discussion, see Wikipedia's fun list of exceptions to conservation of mass: http://en.wikipedia.org/wiki/Conservation_of_mass#Exceptions...

leephillips• 12 years ago

Mass by itself is only conserved in nonrelativistic classical physics. When you are in a relativistic regime the conserved quantity is a combination of momentum and energy. (You've probably seen E = mc^2, which shows that mass and energy can be transformed into each other.)

ktran03• 12 years ago

Wiki:

The law of conservation of mass, or principle of mass conservation, states that for any system closed to all transfers of matter and energy (both of which have mass), the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed.

oddthink4• 12 years ago

Wait, what? Photons have no mass, but they have energy. Ergo, that "both of which have mass" is flat-out wrong. Methinks wikipedia has problems.

timnic2• 12 years ago

Mass is not a conserved quantity. Energy for example is a conserved quantity. So like in a nuclear fission reaction we loose mass but this lost mass is then converted into energy. I have not read the article in detail, but I suppose they want to turn part of the photons energy into masses for the electron and the positron. Mass and energy are linked via E = mc^2.

millstone2• 12 years ago

In fact, both energy and mass are conserved. If you accept e=mc^2 as "true," it's easy to show.

If energy is conserved and mass is not, then what can E=mc^2 possibly mean? Is it a relation, like F=ma? Then if E is constant and of course c is constant, then m must be constant too.

Or is it an exchange rate: you can convert this much mass into that much energy? But then energy is no longer conserved, if you can make it from mass.

Last try. Maybe e=mc^2 means, within a given quantity of mass, there is necessarily a minimum energy? And this is true, but notice that the equation is phrased as an equality. Equalities go both ways: we can just as easily derive m=e/c^2, and now the "minimum energy" idea runs aground.

In modern interpretations, energy and mass are both conserved, and e=mc^2 is understood to be the energy in the rest frame of the system. Individually photons are massless, but multiple photon systems can and usually do have mass. The price we pay for conceiving of mass as conserved and invariant is that it no longer adds nicely.

th0ma5• 12 years ago

Black holes probably do this?

ToastyMallows• 12 years ago

How much energy is this photon/photon collier going to take? If a future experiment works, could we use this created matter to turn around and use it as energy? Or would that not be possible (i.e. - The energy used is far greater than the energy gained)

timnic2• 12 years ago

No, the energy gained will be equal or (most likely) less than the energy used. This is because we have conservation of energy, so a process like

energy (the original photons) -> matter (electron/positron) -> energy

can not produce more energy than was put in.

Retric• 12 years ago

In cases like this energy is not really what you want to talk about as that's always constant it's USEFUL ENERGY which is interesting.

ximeng• 12 years ago

Can anyone explain the vertical lines in the space time diagrams? Presumably not infinite velocity?

yk• 12 years ago

They are not space time diagrams, they are Feynman graphs. Technically they are a clever way to write down the terms of a series expansion. In the convention used, on the left hand side are the incoming particles and the outgoing particles are on the right. The internal lines and vertices are just representations of formulas, and the important thing is only the topology of the graph.

However one of the really great things of Feynman graphs is, that they admit a easy interpretation about what is happening. Then the interior lines are interpreted as virtual particles that are created during the reaction, but since they are virtual they do not really have a defined speed, so the lines are just drawn like that.

jessriedel2• 12 years ago

In fact, Feynman diagrams are spacetime diagrams. (They are commonly computed in momentum space, i.e. Fourier space, but you can also do them in normal position space.) When you draw a Feynman diagram, the vertices correspond to actual points in spacetime, which are then integrated over a la the path integral.

jessriedel2• 12 years ago

Yes, it's infinite velocity. When you compute an amplitude from a Feynman diagram, you sum (integrate) over intermediate particle paths that are superluminal. The math is structured in a way that these contributions cannot actually be used to send signals, but the contributions are crucial and cannot be discarded. Essentially, they represent the relativistic generalization of the effect where one particle in a Bell pair "influences" another over a spacelike separation, but in a subtle and spooky way that cannot produce superluminal signaling.

dmead• 12 years ago

there is no way this is not sensationalized.

NickM• 12 years ago

Probably a long way off, but I can't help but imagine the kind of amazing applications something like this might have. If we could reliably capture and store the resulting positrons, then recombine them with electrons later to release the energy and harness it somehow, I'd imagine this could make for an energy storage system with some really interesting properties.

fixedd• 12 years ago

Like the fact that light doesn't take up any space, so you could theoretically store an infinite amount of energy?

gliese1337• 12 years ago

Sorry, doesn't work. Light still exerts pressure, so even if you could losslessly trap light in a storage container indefinitely, the container would explode long before the energy density became 'infinite'. Furthermore, the energy and momentum in light contributes to the gravitational field, so even if you could make an infinitely strong mirror-box, pumping too much energy into it would eventually result in collapsing into a black hole.

troymc2• 12 years ago

The idea is to store the positrons, and positrons aren't light.

troymc2• 12 years ago

It is an interesting idea, but there are other ways, probably easier, to get the positrons. For example, some radioisotopes emit positrons as part of their natural radioactive decay process. See:

http://arstechnica.com/science/2011/02/positrons-at-center-o...

dang• 12 years ago

A dupe of https://news.ycombinator.com/item?id=7763711.

menubar• 12 years ago

Sounds like this theory could lead to creating one heck of a weapon, Dr. Venture.

Scientists discover how to turn light into matter after 80-year quest

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