[FreshMadEagr]

Would it be possible to create matter from energy? Like a reversed nuclear reaction? Has it been done? How would it work?

I can only assume it would require massive amounts of energy, and would not have any practial near-term applications, but maybe a possibility for propulsion in interstellar space travel in a few thousands of years? :-p
Create matter from energy -> gravity pulls spaceship -> Convert matter back to energy -> back to step one :confused:

[ecoli]

It makes sense to me that this could be done, though I don't know the science behind it. A nuclear reaction does convert matter into energy, so why not the other way around.

[timo]

>> Would it be possible to create matter from energy? Like a reversed nuclear reaction?
Generally: Yes.

>> Has it been done? How would it work?
Extremely short-lived heavy particles are produced in particle accelerators by shooting particles with very high kinetic energy at each other, so I´d say that´s transfering energy into matter. Though, I´m not completely certain if the net rest mass after the collision is higher than the rest mass of the original particles as they are probably destroyed in the collision. But it should be possible to get a win in rest mass, theoretically. The nuclear physicists here should know that.
Another process that actually happens and is sometimes taken into account for calculations is that photons (~light) can decay into an electron and an anti-electron. But I don´t know if this process is actually used on purpose (like for creating anti-electrons).

>> I can only assume it would require massive amounts of energy ...
The minimum energy required would be given by E=m*c² with c being the speed of light, m being the (rest) mass you want to create and E being the required energy. Calculate that out for 1 kg and see if you consider it much.

>> ... and would not have any practial near-term applications
Trying to create the particles predicted by theory is actually a current application.

>> Create matter from energy -> gravity pulls spaceship -> Convert matter back to energy -> back to step one
I don´t have a good answer on this so I´ll try this one: There is probably no point in creating matter to get more kinetic energy from falling towards a planet rather than using the energy to increase your ships kinetic energy (accellerate) without taking that detour.

[Klaynos]

If this was impossible then there would be no heavier elements than iron as this has the highest binding energy/nucleon.

It is belived it happens in supernova's

[swansont]

Quote

If this was impossible then there would be no heavier elements than iron as this has the highest binding energy/nucleon.

It is belived it happens in supernova's

But that's not creating matter, in the sense that all of the nucleons already exist.

[Klaynos]

it is creating matter as the amount of mass afterwards is greater than the mass of the sum of it's parts...

[ydoaPs]

it can happen and DOES happen. in fact, it can happen with 0 net energy. they are called virtual particles.

[swansont]

yourdadonapogos said:

it can happen and DOES happen. in fact, it can happen with 0 net energy. they are called virtual particles.

I wouldn't count virtual particles as matter creation. There is a reason they are called virtual, after all.

[Gilded]

It would be rather awesome though if you could just collide two high-energy photons into each other to make a positron or something. :))

[ed84c]

Photons (again badly quoting a book i read a while ago) sometimes spotaniously create electrons, when they inereact with 'virtual electrons'

[swansont]

ed84c said:

Photons (again badly quoting a book i read a while ago) sometimes spotaniously create electrons, when they inereact with 'virtual electrons'

I think it creates the particle/antiparticle pair, by supplying the required energy, e.g. in Hawking radiation.

Photons will be able to create particle/antiparticle pairs if they have sufficient energy and some other particle around to conserve momentum. You can end up with a net amount of matter after all is said and done because of CP violations, which are seen in e.g. K and B mesons

[[Tycho?]]

Extremely high energy gamma rays produce a particle/antiparticle, which then hit and destroy themselves, emitting two photons each having less the energy of the first.

[Severian]

is the creation of matter from energy. All it requires is for the photons to have total energy in the centre of mass frame greater or equal to twice the mass of the electron (about 1 MeV). So this is very easy to do.

[Gilded]

Hmmh. I have no idea what that equation means, but if you had a block made of nuclei that emit about 0.5 MeV photons when they decay, a matter creation event could take place inside such block? :)

[swansont]

Gilded said:

Hmmh. I have no idea what that equation means, but if you had a block made of nuclei that emit about 0.5 MeV photons when they decay, a matter creation event could take place inside such block? :)

No. You need ~1.02 MeV to create the e⁺e^- pair. When they annihilate, though, they must give off two photons (or more) in order to conserve momentum, so these will be ~.51 MeV each.

[JaKiri]

Quote

Create matter from energy -> gravity pulls spaceship -> Convert matter back to energy -> back to step one :confused:

How is that even supposed to work efficiently? Or at all?

Klaynos said:

it is creating matter as the amount of mass afterwards is greater than the mass of the sum of it's parts...

Sort of. The difference is down to the difference in Nuclear Binding Energy, so it's almost exactly the opposite of a nuclear reaction which gives out energy.

[ed84c]

Quote

How is that even supposed to work efficiently? Or at all?
.

Hes saying that you make matter out of energy, and use the gravity from that matter to propel (or pull) a space ship.

I think the second law of thermodynamics may have something to say about that though.....

[swansont]

Quote

Hes saying that you make matter out of energy, and use the gravity from that matter to propel (or pull) a space ship.

I think the second law of thermodynamics may have something to say about that though.....

Einstein, too. You have to view the gravity relativistically, not classically.

[Severian]

Quote

Create matter from energy -> gravity pulls spaceship -> Convert matter back to energy -> back to step one :confused:

This was actually the original explanation of FTL in Star Trek. They fire gravitons out the front of the ship, so that space is warped and 'shrunk', then pass over the shrunk space and let it expand behind. The idea was that since one is passing over less space, one can effectively travel faster than c.

They forgot that the gravitons can't travel faster than c though, so you can't warp the space fast enough to allow FTL travel. (in princple though, you could use it to make a ship faster (<c), although it would be very inefficient.)

[Gilded]

I'm starting to think I'd like to see some statistics that state the percentual amount of Star Trek watching physicists among all physicists. :))