e=mc2, does this mean that we can make atoms out of energy?

[coke]

I'm not sure what you and swansont mean by conserving momentum...

Perhaps the 1mm gold sheet they put in front of the laser here?

 

I know you can already make electrons and positrons from high energy photons,

Its clearly described in that link... which i think is a very cool link by the way...

 

I wonder if the gold even gets ruined in that experiment, or if antimatter can be created indefinitely without replacing the gold...

 

"The California researchers estimate that with every shot of their laser, which fires every 30 minutes, they create about 10 billion positrons, also called anti-electrons." (source)

Edited April 6, 2009 by coke

[Mr Skeptic]

Momentum = p = (relativistic mass * velocity). For a photon, this is p=E/c, for a massive particle [math]p=\frac{mv}{\sqrt{1 - (v/c)^2}}[/math]. To convert the photon into particle pairs, some of the photon's energy (E = relativistic mass * c²) is converted into the particle pair, which have both relativistic mass and non-zero rest mass. You can consider the relativistic mass to be a unit of energy, which you can multiply by the speed of light squared to get energy in joules. Anyhow, due to having rest mass, the particles cannot travel at the speed of light and so must travel slower. Thus they can't conserve both energy and momentum as that would require them traveling at c.

 

Yes, the gold sheet is sufficient to satisfy conservation of momentum. Some of the photon's momentum goes to a gold atom, and the remainder is divided among the particle pair.

[einstein's bro]

I believe theoretically on a large enough scale this would work

[Deerajal]

yes it is possible matter and energy are interchangeable.

[jake.com]

c=speed of light.

 

E²=m²c⁴+p²c²

 

Do you have any idea how much energy you're talking about?

 

How much energy would this take, hypothetically?

[swansont]

How much energy would this take, hypothetically?

 

Ho much mass are you talking about? Multiply it by 9 x 10^16 m^2/s^2. If the mass is in kg, the answer will be in Joules.

[Norman Albers]

Yes but at Stanford a handful of years ago Seb Doniach told me they were cross-aiming duelling x-ray lasers from the two storage rings, to actually "cook the vacuum" and create particle pairs. I've not kept tabs on this.

[swansont]

Yes but at Stanford a handful of years ago Seb Doniach told me they were cross-aiming duelling x-ray lasers from the two storage rings, to actually "cook the vacuum" and create particle pairs. I've not kept tabs on this.

 

A two-photon reaction from counter-propagating beams would not violate conservation of momentum. So unless there's some other restriction that I can't think of, that could work.

[Norman Albers]

"Boiling the vacuum" he called it. He retired as a QM professor. . . . . . . . On a different note I am looking at a paper of the Astronomical Society of Australia by Qinghuan Luo and R.J.Protheroe , Vol.15, #2, called "Pair production by photons in the field of the nucleus" and this sounds like what Swansont said. These authors are looking at polar caps of pulsars: "Resonant inverse Compton scattering above polar caps... for young pulsars". I quote the text: "Electron positron pair cascades can be started by accelerated ions in thermal photon fields. A photon can decay into an electron positron pair in the Coulomb field of a nucleus when the center of momentum frame energy exceeds the rest mass of the numcleus plus two electrons... This condition can be satisfied for soft photons from the polar cap in the presence of accelerated ions..." It seems to me they include the strong magnetic field lines from the pole and these are confining the ions. Check out the specs in the discussion: star surface temps are 5 million Kelvins and 100 million for the caps. The B-field is estimated at 3 x 10^9 Teslas, whoa Betty. solidspin could really do some analysis with such a magnet! Cameron, wherever there are such large amounts of energy sloshing around, different forms have probabilities of manifesting. First we know we have to satisfy conservation of momentum and of energy, as well of charge, in the possible outcomes.

Edited May 5, 2009 by Norman Albers

[elas]

Before this question can be answered there is a requirement to define mass, matter and anti-matter, the solution follows on. Einstein found that the terms mass and energy are inter-changeable quantities; he did not prove that they are separate entities. Without mass there is no energy; without particles there is no mass.