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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:

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>> 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.

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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.

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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

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[math]\gamma \gamma \to e^+e^-[/math] 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.

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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.

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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?

 

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.

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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.....

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Hes saying that you make matter out of energy' date=' 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.....[/quote']

 

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

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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.)

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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. :))

 

I know quite a few physicists, spending all my days in a school of physics at a university, and I can happily say none of them belive star trek/watch it on a regular basis, that I know of and I'm sure it would have come up in conversation at some point... Well it has but only sniggering at some of the ideas...

 

Although there where "scientists" that where consulted about the original star trek series...

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I know quite a few physicists' date=' spending all my days in a school of physics at a university, and I can happily say none of them belive star trek/watch it on a regular basis, that I know of and I'm sure it would have come up in conversation at some point... Well it has but only sniggering at some of the ideas...

 

Although there where "scientists" that where consulted about the original star trek series...[/quote']

 

ST:TNG had a science consultant who has a PhD in applied Physics from Cornell. But the writers sometimes overrule the science consultant, and it's science fiction, after all.

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I don't know about the powering up a spaceship bit, but doesn't nature create matter from energy all the time, i.e. via the creation process and new cell growth? Maybe we could somehow learn from nature if we wanted to create new matter.

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I don't know about the powering up a spaceship bit, but doesn't nature create matter from energy all the time, i.e. via the creation process and new cell growth? Maybe we could somehow learn from nature if we wanted to create new matter.

 

New cells use existing atoms and molecules.

 

I echo Sayo's query. "The creation process" reminds me of this Sidney Harris cartoon - I think you need to be more explicit in step 2.

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