
Physicists believe they can create matter from colliding photons - stonlyb
http://www.theguardian.com/science/2014/may/18/matter-light-photons-electrons-positrons
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dspeyer
The timeline:

    
    
        1934: This is predicted
        1997: This is done http://www.nytimes.com/1997/09/16/science/scientists-use-light-to-create-particles.html
        2014: We will "demonstrate the feat within the next 12 months"
        2015: Didn't bother

~~~
TTPrograms
The 1997 experiment is slightly different, as it involves electrons instead of
just photons. See
[https://en.wikipedia.org/wiki/Schwinger_limit](https://en.wikipedia.org/wiki/Schwinger_limit):

"Photon–photon scattering and other effects of nonlinear optics in vacuum is
an active area of experimental research, with current or planned technology
beginning to approach the Schwinger limit.[5] It has already been observed
through inelastic channels in SLAC Experiment 144.[6][7] However, the direct
effects in elastic scattering have not been observed. As of 2012, the best
constraint on the elastic photon–photon scattering cross section belongs to
PVLAS, which reports an upper limit far above the level predicted by the
Standard Model.[8] Proposals have been made to measure elastic light-by-light
scattering using the strong electromagnetic fields of the hadrons collided at
the LHC.[9] Observation of a cross section larger than that predicted by the
Standard Model could signify new physics such as axions, the search of which
is the primary goal of PVLAS and several similar experiments. Even the
planned, funded ELI–Ultra High Field Facility, which will study light at the
intensity frontier, is likely to remain well below the Schwinger limit[10]
although it may still be possible to observe some nonlinear optical
effects.[11] Such an experiment, in which ultra-intense light causes pair
production, has been described in the popular media as creating a "hernia" in
spacetime.[12]"

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eloff
Has anyone ever wondered why the C^2 in E=MC^2 I'm sure it wasn't chosen at
random just because a large constant was needed, it must fall out of some
other physics equations.

But still, what does that mean? What does the transmutation of energy into
mass or visa versa have to do with the universal speed limit?

I am always struck by the inexplicable power of mathematics to describe the
physical laws of the universe, in often simple equations like this. It doesn't
have to be that way as far as we know.

~~~
raziel2702
No one has answered your question. There is no answer really to your question.
At least, not to the level that you are asking. Why is c^2 in that equation?
What does it mean? We don't know. It's a deeper level of understanding that we
haven't achieved.

Another similar question would be why does pi come up in everything? There's a
lot of physics where pi comes up and we don't know why.

~~~
dnquark
The original question has perfectly satisfying explanations accessible to
anyone who knows algebra and is willing to spend a few weeks studying special
relativity. cynicalkane above provides a great intuitive summary.

Likewise, generally speaking, when pi comes up in physics equations it is a
geometric factor, either having something to do with the bona fide geometry of
the system (e.g. the capacitance of a sphere) or with normalizing some
relevant probability distributions. Name one example where we struggle to
understand where pi comes from in physics formula!

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fatuna
This article appears to be 1,5 years old. So at least the 1 year deadline was
missed.

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jp555
If we could trap those positrons somehow in large numbers...

Antimatter production?

~~~
ars
There are much easier ways to make positrons.

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dosh
This is exciting. Not sure how they will go from electron-positron creation to
protons which needs quarks, but according to
[https://en.wikipedia.org/wiki/Matter_creation](https://en.wikipedia.org/wiki/Matter_creation)

Summary: Matter creation is the conversion of massless particles into one or
more massive particles. Since all known massless particles are bosons and the
most familiar massive particles are fermions, usually what is considered is
the process which converts two bosons (e.g. photons) into two fermions (e.g.,
an electron–positron pair). This process is known as pair production.

So technically, it is a matter creation.

~~~
KenoFischer
In theory all you have to do to get protons is crank up the energy.

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venomsnake
Can anyone explain when and where the Higgs enters the reaction? That is the
most interesting for me, since we don't have anti Higgs.

~~~
drdeca
I thought that the Higgs Boson was its own antiparticle, like the photon? I am
not sure.

~~~
georgeaf99
I will preface this by saying my understanding of particle physics is very
basic...

Yes, that is correct. The Higgs particle is also extremely unstable and decays
into two photons almost immediately.

~~~
eli_gottlieb
Wait, why does the field-quantum for inertia decay into the field-quantum for
light?

~~~
drdeca
I am not at all sure, but my guess is that:

the results must be electrically neutral in total

the results must have the same total spin (0) (this might require that all the
resulting things have spin 0 but I don't know)

the results must conserve a variety of other quantities,

I think maybe pairs photons are (one of?) the only things that meets these
requirements?

I'm not sure. I'm mainly guessing.

But, if proton collisions can cause Higgs Bosons, I think maybe the idea is
that so long as all the quantities are conserved(charge, mass, color, spin,
momentum, etc. etc.), any particles with small enough energy can be the result
maybe?

I don't know if that is the idea. I'm just guessing based on how things are
described wrt protons, but I might be misinterpreting things.

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ambrop7
I imagine "matter" as commonly understood would contain at least electrons and
protons, but they would just be making electrons and positrons. Can we make
protons/neutrons out of light too?

~~~
GFK_of_xmaspast
[https://en.wikipedia.org/wiki/Positronium](https://en.wikipedia.org/wiki/Positronium)

~~~
pythonlion
cool but there are no quarks involved..(?)

~~~
GFK_of_xmaspast
Who says there has to be?

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negamax
So was light first or matter?

Was there early radiation (light != visible light only) which created matter.
H -> He -> Stars. Or matter preexisted?

~~~
ackfoo
In the beginning, there was nothing. But it was a very active kind of nothing
that, because of the Uncertainty Principle, allowed bits of energy to be
borrowed from nothing, leaving behind holes as a sort of IOU.

The likelihood of a virtual particle pair arising was inversely proportional
to the energy difference across the pair. Since you need a fair bit of energy
to do anything interesting, nothing happened for a very long time.

However, since there was an abundance of very long time, eventually two of the
photons borrowed out of the vacuum with sufficient energy interacted in such a
way as to give rise to matter.

Multiply that very long time by all of the matter in the universe (a very long
time, squared; lucky we had lots of it) and we have beaches and sunsets.

The only remaining question is how all that matter was gathered into the
singularity that gave rise to our present universe about 13.8 (or whatever) By
ago. Maybe it accreted out of the original matter over another very long time.

Or maybe the idea that when you run the expansion of the universe backward you
get a singularity is wrong. Maybe matter arising out of the vacuum disappears
back where it came from when you run the picture backwards and it only looks
like the universe started 13.8 By ago because that's how far out the event
horizon sits. Maybe the cosmic background is the signature of the vacuum-
derived pairs creating matter. Maybe this experiment will demonstrate an
alternative origin for the cosmic background.

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maplechori
Are we going to be able to materialize dinner soon?

~~~
clavalle
1 lb of food would take about 10 megatons of TNT of energy. I'm not sure you'd
want whatever that device is sitting on everyone's kitchen counter.

~~~
rm_-rf_slash
I imagine if you had that kind of Star Trek replicator technology it would be
more feasible to use existing matter and rearrange it as desired.

~~~
clavalle
Plus, a starship is already strapped to a huge energy source so the additional
risk is probably minimal.

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grondilu
Didn't we know that ever since E=mc² ?

~~~
garrettgrimsley
They knew that it was possible in theory, as the article mentioned. This
experiment will be a concrete demonstration of that theory.

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mrerrormessage
If this can be made practical at any scale, I think the most exciting
applications will be in long-range space drives. Although it sounds as though
immense amounts of energy are needed, not needing to take along matter to
eject in order to move is a game changer for space exploration.

~~~
vbezhenar
I think you can use photon engines in the first place.

~~~
KenoFischer
Yep, you'd be significantly better off just shining the laser behind you.

