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sleepsleep



Joined: 05 Oct 2006
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sleepsleep
i think, this is simply amazing!

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

Quote:
Breit and Wheeler suggested that it should be possible to turn light into matter by smashing together only two particles of light (photons), to create an electron and a positron – the simplest method of turning light into matter ever predicted. The calculation was found to be theoretically sound but Breit and Wheeler said that they never expected anybody to physically demonstrate their prediction. It has never been observed in the laboratory and past experiments to test it have required the addition of massive high-energy particles.


so, next step is everybody got a light beamer, something like 3D printer at home, then object data, on your light beamer, then you got a solid physical object later.

then everything exists as some sort of how to combine information.
Post 19 May 2014, 16:22
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revolution
When all else fails, read the source


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revolution
It would take a LOT of light to create the sort of matter you are thinking of. Remember that E = mc^2, so rearranging gives m = E/c^2. I'll leave it to you to figure out just how much energy is required to make even one gram of matter. Being VERY generous and assuming a perfect 100% conversion efficiency the energy requirements are huge.

So, no, it is merely an academic curiosity.
Post 19 May 2014, 16:27
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sleepsleep



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sleepsleep
i assume energy to tear apart an atom is equal to energy needed to combine photons into atom?
but it just amazing, we are advancing,
Post 19 May 2014, 16:36
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neville



Joined: 13 Jul 2008
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neville
revolution wrote:
It would take a LOT of light to create the sort of matter you are thinking of. Remember that E = mc^2, so rearranging gives m = E/c^2. I'll leave it to you to figure out just how much energy is required to make even one gram of matter. Being VERY generous and assuming a perfect 100% conversion efficiency the energy requirements are huge.

So, no, it is merely an academic curiosity.
Ye have little faith Wink The truth is there is really nothing new here. The creation of electron-positron pairs from high-energy gamma rays was demonstrated 80 years ago in the 1930's. The "light" referred to in the article must also be gamma rays (or at least high-energy X-rays) which are certainly electromagnetic waves but not exactly visible light Smile

E = 2*Me*c^2 where Me=mass of electron=9*10^-31kg gives the minimum energy required = about 2*10^-13 Joule

You then equate that to E = h*f where h = Planck's constant = 6.6*10^-34 J/Hz which gives the minimum "light" frequency f = 2*10^20 Hz

Visible light is at least 5 orders of magnitude lower in frequency i.e. >10000 times longer wavelength.

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Post 21 May 2014, 07:57
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revolution
When all else fails, read the source


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revolution
I thought that it was only a theory that was demonstrated ~80 years ago. And at that time it was thought not possible to do it in reality. Which is where this "news" was supposed to be something interesting because a practical method has been discovered to demonstrate it. Although, as is usual with these things, no such device has been built as yet so it is all still just a theory waiting to be tested.
Post 21 May 2014, 08:15
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edfed



Joined: 20 Feb 2006
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edfed
science for dummies is full of inexact claims. it is the sad effect of reality shows, writing "false" statements just to gain more popularity. if the title was: "scientist created electron positron couples using high energy gamma rays", i think there would be far less comments on the net about it.
Post 21 May 2014, 09:23
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neville



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neville
Very true edfed.

Iirc it was Paul Dirac who first proposed the theory in ~1930 (maybe the late 1920's) but no credit is given to him in the Imperial article. Afaik Dirac himself never demonstrated it but I'm certain it had been demonstrated by at least the late 1930's. I can remember seeing an old cloud chamber photograph of an electron and positron in a magnetic field recoiling spirally in opposite directions and the incident energy source was gamma rays. It's probably on the net somewhere by now...

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Post 21 May 2014, 23:54
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Dr F



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Dr F
the evil will be purged from this world and some horrors as well via gamma rays and the like as recommended for those trying to escape to outer space.
Post 22 May 2014, 13:21
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revolution
When all else fails, read the source


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revolution
Dr F wrote:
the evil will be purged from this world and some horrors as well via gamma rays and the like as recommended for those trying to escape to outer space.
So if we convert ourselves to gamma rays then we can escape to outer space. Sounds plausible actually. But I am concerned about the process of converting everything back from the gamma rays. Confused
Post 22 May 2014, 13:27
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DOS386



Joined: 08 Dec 2006
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DOS386
> to create an electron and a positron – the simplest method of turning light into matter ever predicted

1. This had been already around for centuries
2. You also need protons (and get antiprotons as bonus)
3. You also need neutrons (if you want to brew anything more than just hydrogen)
4. You need a good and safe trash bin where you can discard the positrons and antiprotons

Hard work @you Wink

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Post 22 May 2014, 14:47
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gens



Joined: 18 Feb 2013
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gens
revolution wrote:
Dr F wrote:
the evil will be purged from this world and some horrors as well via gamma rays and the like as recommended for those trying to escape to outer space.
So if we convert ourselves to gamma rays then we can escape to outer space. Sounds plausible actually. But I am concerned about the process of converting everything back from the gamma rays. Confused


make sure you don't bounce off the ionosphere (y)
Post 22 May 2014, 14:55
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JohnFound



Joined: 16 Jun 2003
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JohnFound
@DOS386 - you can simply gather the protons and electrons as hydrogen and positrons and anti-protons as anti-hydrogen in two big tanks and then burn them in the photon propulsion engine of the star-ship.
Post 22 May 2014, 16:03
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Xorpd!



Joined: 21 Dec 2006
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Xorpd!
The time-reversed event is electron-positron annihilation, which is sufficiently commonplace that PET scans are based on detecting the events. Also pair production by single photons colliding with matter is commonly observed, but to get electron-positron pairs from colliding photons you either need two streams of gamma rays beamed in opposite directions at very high intensity to observe any events or gamma rays of much higher energy colliding with a high-intensity laser beam.
I'm not sure from reading the URL above, but it seems that they may be looking for > 2 photon events, so not technically the time-reversal of pair annihilation.
Post 26 May 2014, 22:45
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