Results 1 to 12 of 12

Thread: 30x the speed of light?

  1. #1
    Join Date
    Jun 2011
    Posts
    1,494

    30x the speed of light?

    They are not referring to the tunnelling effect here so I do not understand how they could have achieved 30x the speed of light:
    https://phys.org/news/2019-04-resear...o-control.html

    Are they breaking Relativity?


    Sent from my iPhone using Tapatalk

  2. #2
    Join Date
    Sep 2003
    Location
    The beautiful north coast (Ohio)
    Posts
    48,678
    Here, for reference, is the paper.

    Abstract:
    Controlling the group velocity of an optical pulse typically requires traversing a material or structure whose dispersion is judiciously crafted. Alternatively, the group velocity can be modified in free space by spatially structuring the beam profile, but the realizable deviation from the speed of light in vacuum is small. Here we demonstrate precise and versatile control over the group velocity of a propagation-invariant optical wave packet in free space through sculpting its spatio-temporal spectrum. By jointly modulating the spatial and temporal degrees of freedom, arbitrary group velocities are unambiguously observed in free space above or below the speed of light in vacuum, whether in the forward direction propagating away from the source or even traveling backwards towards it.
    This appears to be a so-called "fast light" experiment. Here is a very good explanation of fast light. And no, it is completely consistent with Relativity.

    The speed of light in vacuum (c ≈ 3 108 m/s) is an important physical constant that appears in Maxwell’s theory of electromagnetism. For this reason, scientists have endeavored to measure it with very high precision, making it one of the most accurately known of all physical constants. The situation becomes murkier for a slightly different situation: Send a pulse of light through a dispersive optical material rather than vacuum, and bizarre things start to appear. For example, under conditions such that the dispersion of the medium is anomalous over some spectral region,1 as described in greater detail below, it is possible to observe the peak of a pulse of light apparently leaving a piece of dispersive material before it enters.
    The possibility of such “fast light” behavior has been known for nearly a century and has been the source of continued controversy and confusion. Some of the controversy arises because some people interpret Einstein’s special theory of relativity as placing a speed limit of c on any sort of motion. Yet, a rather simple mathematical proof shows that fast light behavior is completely consistent with Maxwell’s equations that describe pulse propagation through a dispersive material and, hence, does not violate Einstein’s special theory of relativity, which is based on Maxwell’s equations. Although the proof is straightforward, great care must be taken in interpreting the special theory of relativity and in determining whether experimental observations are consistent with its predictions.

    From our point of view, the special theory of relativity places a speed limit on the transfer of information between two parties, and all experiments performed to date are consistent with the speed limit being interpreted in this manner.

    To understand the basics of fast-light pulse propagation, it is crucial to realize that there are many quantities that can be introduced to describe the speed at which a light pulse moves through a material system.2 This confusing situation arises from the fact that a pulse propagating through any material system will experience some level of distortion — e.g., it spreads out in time and reshapes — and, hence, a single velocity cannot be used to describe the motion of the pulse.
    At night the stars put on a show for free (Carole King)

    All moderation in purple - The rules

  3. #3
    Join Date
    Jun 2011
    Posts
    1,494
    Quote Originally Posted by Swift View Post
    Here, for reference, is the paper.

    Abstract:


    This appears to be a so-called "fast light" experiment. Here is a very good explanation of fast light. And no, it is completely consistent with Relativity.
    Interesting! Thank you very much...!


    Sent from my iPhone using Tapatalk

  4. #4
    Join Date
    Sep 2004
    Location
    South Carolina
    Posts
    2,261
    I read this article, knew right away I was going to interpret it incorrectly, and deliberately forgot about it. I did the right thing.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    Mark Twain, Life on the Mississippi (1883)

  5. #5
    Join Date
    Aug 2003
    Posts
    1,895

    Fast Than Light Light

    My understanding of Special Relatively tells me this isn't possible. But, if anything can go ftl, it would have to be light. If light can go 30% ftl, would that make ftl communication possible? Or would that violate causality?
    http://www.spacedaily.com/m/reports/...kward_999.html

  6. #6
    Join Date
    Aug 2005
    Location
    NEOTP Atlanta, GA
    Posts
    2,619
    Already being discussed - sort of - here: http://forum.cosmoquest.org/showthre...speed-of-light

  7. #7
    Join Date
    May 2008
    Location
    The Netherlands
    Posts
    15,141
    Superluminal's thread from Science and Technology merged.
    ____________
    "Dumb all over, a little ugly on the side." -- Frank Zappa
    "Your right to hold an opinion is not being contested. Your expectation that it be taken seriously is." -- Jason Thompson
    "This is really very simple, but unfortunately it's very complicated." -- publius

    Moderator comments in this color | Get moderator attention using the lower left icon:
    Recommended reading: Forum Rules * Forum FAQs * Conspiracy Theory Advice * Alternate Theory Advocates Advice

  8. #8
    Join Date
    Aug 2013
    Posts
    366
    Quote Originally Posted by Swift View Post
    This appears to be a so-called "fast light" experiment.
    I recall that previous much older FTL claims, particularly cumulative observations involving prisms, were disputed due to timing lag involving total internal reflection (TIR). Is this still the case?

    https://en.wikipedia.org/wiki/G%C3%B...ntum_tunneling

  9. #9
    Join Date
    Oct 2005
    Posts
    26,511
    The short answer is, group velocity can be larger than c, but no information can be communicated faster than c. You can think of it this way. If I set up a "wave" in a sports stadium, I can make that wave move any speed I want, including 30c, just by giving people instructions beforehand of exactly when to stand up, and they all have synchronized watches and stand up when the instructions say. What I could not do is send the instructions themselves faster than c.

  10. #10
    Join Date
    Aug 2006
    Posts
    3,293
    Quote Originally Posted by Ken G View Post
    The short answer is, group velocity can be larger than c, but no information can be communicated faster than c. You can think of it this way. If I set up a "wave" in a sports stadium, I can make that wave move any speed I want, including 30c, just by giving people instructions beforehand of exactly when to stand up, and they all have synchronized watches and stand up when the instructions say. What I could not do is send the instructions themselves faster than c.
    It sounds a little like the "superluminal flashlight" thought experiment.

    From 223,000 miles away, I can sweep a spotlight across the surface of the Moon arbitrarily fast - easily faster than light.
    But, when I examine what that light is doing, I see that no individual photon is exceeding c.
    It is only inasmuch as I define the "spotlight" as if it is a real discrete thing that I can say "it" is moving faster than c.

  11. #11
    Join Date
    Aug 2013
    Posts
    366
    Quote Originally Posted by Ken G View Post
    The short answer is, group velocity can be larger than c, but no information can be communicated faster than c. You can think of it this way. If I set up a "wave" in a sports stadium, I can make that wave move any speed I want, including 30c, just by giving people instructions beforehand of exactly when to stand up, and they all have synchronized watches and stand up when the instructions say. What I could not do is send the instructions themselves faster than c.
    So it is still the case.

  12. #12
    Join Date
    Oct 2005
    Posts
    26,511
    Quote Originally Posted by DaveC426913 View Post
    It sounds a little like the "superluminal flashlight" thought experiment.

    From 223,000 miles away, I can sweep a spotlight across the surface of the Moon arbitrarily fast - easily faster than light.
    But, when I examine what that light is doing, I see that no individual photon is exceeding c.
    It is only inasmuch as I define the "spotlight" as if it is a real discrete thing that I can say "it" is moving faster than c.
    Yes, that's similar, a way to make a feature move faster than c, without any information traveling with that feature such that it could carry a communication with it.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •