The evolution of lasers...

Discussion in 'Physics' started by cmartinez, Aug 1, 2016.

  1. cmartinez

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    I've just read this rather interesting article:

    And found two outstanding facts:
    ...in the 1980s we paid $200,000 for a laser that I could buy today for less than $5

    That's pretty impressive... for a guy whose teenage years where lived in the 80's, it brings the economics of technology in perspective.

    But this other one, is simply mind boggling:
    Well, a project called the Extreme Light Infrastructure is now being built in Romania. It will focus laser pulses lasting less than a trillionth of a second to intensities so high that they can ionise the vacuum, creating positrons and electrons. It takes black holes to do that in nature.

    How is it possible to actually excite the vacuum to the point of ionization? Is it because the photon energy and density is so intense that virtual particles are not allowed to re-collapse on themselves? Would such phenomena make it possible to build an engine capable of propelling a spaceship without needing a propellant?
     
  2. wayneh

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    I'm extremely skeptical of that claim. Fusion reactions can convert energy to mass. This is the opposite of using fusion to release energy, but it's what happens for fusing atoms more massive than iron, if I recall correctly.

    Anyway, I don't think you can shoot pure light energy into the void and get mass out of it.

    Would love to be shown wrong.
     
  3. cmartinez

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    Well, there really are virtual particles out there, and they're responsible for the already proved casimir effect.
    Besides, the article's source is serious enough to at least give it some objective consideration.
     
  4. nsaspook

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    There is a point where it is theorized that EM becomes nonlinear. Schwinger limit

    The field would be so strong it would split apart the vacuum virtual particle/anti-particle pairs before they recombine. The problem is no one really knows if these so called virtual-particles ( disturbance in a field) interactions will result in true matter (most likely not).
     
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  5. cmartinez

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    and that, is what experiments are for... although this one in particular will prove a bit expensive ...
     
    Last edited: Aug 1, 2016
  6. cmartinez

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    Wow!:

    Maxwell's equations predict the impossibility of any but trivial elastic photon–photon scattering. In QED, however, non-elastic photon–photon scattering becomes possible when the combined energy is large enough to create virtual electron–positron pairs spontaneously, illustrated by theFeynman diagram in the adjacent figure.


    The entire article is extremely interesting, especially the last paragraph:

    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 toPVLAS, 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]

    By "hernia" I assume the article means a spacetime rift?

    Thanks for the excellent reference, nsaspook.
     
  7. #12

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    Keep up the research. This is one of the keys to transporter technology. (Beam me up, Scotty.):D
     
  8. shortbus

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    Isn't this similar to what they are trying to do at the NIF(national ignition facility)?
     
  9. cmartinez

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    This is astonishing:

    http://www.foxnews.com/tech/2018/02...nse-than-sun-that-could-tear-space-apart.html

     
  10. nsaspook

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    Sorry, more media hype. Pop-science virtual particle misconceptions. Its the science reporters. Complex ideas often get simplified down, warped and twisted between leaving a scientist's mouth and appearing in print.

    Virtual particles are simply a mathematical artifact of the modeling process, they don't actually exist in modern QFT.
    https://www.physicsforums.com/insights/vacuum-fluctuations-experimental-practice/

    https://www.physicsforums.com/insights/vacuum-fluctuation-myth/
    https://www.physicsforums.com/threads/so-quantum-fluctuations-dont-exist.925247/page-2#post-5843430

    http://www.mat.univie.ac.at/~neum/physfaq/topics/virtcoul
     
  11. cmartinez

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    Unless I've misunderstood what you've said, then how do you explain the very real force exerted by the Casimir Effect? ...
     
  12. nsaspook

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    I will let the Prof. answer that question: https://www.physicsforums.com/insights/author/a-neumaier/
    http://www.mat.univie.ac.at/~neum/physfaq/topics/casimir

    Most of the 'breaking the vacuum' articles are variations on experiments to approach the Schwinger_limit.
    These virtual pairs are not actual particles but they do have real effects in fields.
    https://profmattstrassler.com/artic...ysics-basics/virtual-particles-what-are-they/
     
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  13. nsaspook

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    So, there really is no reason to believe (and many reasons not to believe) that vacuum fluctuations or virtual particles are fundamentally needed for the Casimir Effect. Van der Waals quantum forces from uncertainty in the location/momentum of the electrons (real particles) can be used to explain it.

    https://en.wikipedia.org/wiki/Casimir_effect#Relativistic_van_der_Waals_force


    http://www.sciencemag.org/news/2018...-so-powerful-they-could-rip-apart-empty-space
    Back to the laser, as the science article says correctly "This will be completely new physics". Where have we heard that term before?
     
  14. crutschow

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  15. nsaspook

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    Virtual particles are always a calculation of an effect. What escapes from the macroscopic black hole's event horizon is a real photon generated from a process where virtual particles are used in diagrams to describe that process.

    https://physics.stackexchange.com/questions/251385/an-explanation-of-hawking-radiation
    https://physics.stackexchange.com/a/252183
     
    Last edited: Feb 2, 2018
  16. nsaspook

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    As you can see he didn't really say that in his peer reviewed paper because he's a physicist who understands what virtual particles really are and didn't get his understanding of the true physical process from pop-science articles.
     
  17. crutschow

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    I bow to your expert knowledge.
     
  18. cmartinez

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    I'm glad to learn that the Chinese are not the only ones after this sort of science:

    http://www.iflscience.com/physics/s...ul-they-could-tear-matter-out-of-empty-space/

     
  19. nsaspook

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    Cool, but I still cringe at “break the vacuum” because it's pop-science BS.

    https://www.forbes.com/sites/starts...er-really-rip-apart-empty-space/#15bb1299f4b0
     
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  20. cmartinez

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