Physics for Those in Full Possession of their Mental Faculties

Researchers Develop way to Control Speed of Light, Send it Backward

https://phys.org/news/2019-04-researchers-develop-way-to-control.html?mc_cid=690c4afed3&mc_eid=a8346481b7

That’s the headline at phys.org, who Should Know Better. But that site is not as well-regulated as you might think from the impressive title. Phys.org is to physics as Business Insider is to business — poorly moderated group blogs around a supposed focus of interest.

I’ll cut to the chase. A comment illuminated the problem with the post.

Comment author: antialias_physorg

“*Sigh* this is group velocity. Not velocity of individual photons.
https://en.wikipedia.org/wiki/Group_velocity
It’s like passing a laserpointer accross the face of the moon.
Can the bright spot on the moon APPEAR to move faster than light? Yes.
Does anything in this setup (including information transmission) move faster than light? No.

Speed of light limits aren’t broken, here. It’s achieved with a (very clever) modulation of the beam characteristics with the magnetic and electric fields not at right angles to the direction of propagation but canted sharply forwards/aft.”


That comment is (taken with similar comments further down) the only thing of value on the page. Perhaps the author of the article, “University of Central Florida” could have titled and written the post differently, in a manner which reflects the story being reported upon with more , um, honesty. But this was not done, the article stands or falls as written, and it falls in an atrocious fashion.

The last line of the comment shows its author to be a man of my stripe:

“(Full paper is linked in the article, BTW…so all you nutjobs could have saved your time and just read it before posting your ludicrous comments)”

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15 thoughts on “Physics for Those in Full Possession of their Mental Faculties”

  1. We have anti-Spam software that doesn’t like comments with lots of links.  I think it would have gone into the group if there were less link or broken up into parts.

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  2. 10 Cents:
    We have anti-Spam software that doesn’t like comments with lots of links.  I think it would have gone into the group if there were less link or broken up into parts.

    Ah, yes, the old “It’s not broken, you’re just a moron” solution.  Guilty.

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  3. Haakon Dahl:
    This post was supposed to be in the Smart Rats group.  But that doesn’t work.  Ah, good old WordPress!

    What was the error message you got?  I don’t think the problem was links in the post.  First of all, the maximum number of links in a comment causing it to require moderation (not be marked as spam) is set to 25, and this post had only a few.  Second, I don’t think that limit applies to posts in BuddyPress groups in any case.  There is no BuddyPress setting for a maximum number of links that I can find in its settings.

    I took the HTML text of the original post and posted it in the Sand Box group and it posted just fine.  I did this from my regular user account which has no special administrator privileges.  (I am among the administrators of the Sand Box group, but then you are an administrator of The Smartest Rats in the Lab group so there is no difference there.)

    Can you post anything in that group?  I notice that nothing has yet been posted there.

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  4. No error message.  Post appears to go, but then fails to appear.  I can post there.  Once I replace the “mule” text with the stuff above, the post disappears.

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  5. Haakon Dahl:
    No error message.  Post appears to go, but then fails to appear.  I can post there.  Once I replace the “mule” text with the stuff above, the post disappears.

    What do you mean by “mule” text, and what stuff above?  I am thoroughly confused.  It looks like your most recent post in the group was the full post above, but just with “Mule 2” before the heading.

    Posting items in BuddyPress groups containing HTML mark-up is always an iffy proposition because there is no coherent design for quoting in WordPress and it is a huge pile of ad hoc hacks which nobody understands.  Maybe it doesn’t like a post that begins with an {h1} tag, but then when I posted your original post in the Sand Box, whcih has one,  it posted just fine.

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  6. John Walker:

    Haakon Dahl:
    No error message.  Post appears to go, but then fails to appear.  I can post there.  Once I replace the “mule” text with the stuff above, the post disappears.

    What do you mean by “mule” text, and what stuff above?  I am thoroughly confused.  It looks like your most recent post in the group was the full post above, but just with “Mule 2” before the heading.

    Posting items in BuddyPress groups containing HTML mark-up is always an iffy proposition because there is no coherent design for quoting in WordPress and it is a huge pile of ad hoc hacks which nobody understands.  Maybe it doesn’t like a post that begins with an {h1} tag, but then when I posted your original post in the Sand Box, whcih has one,  it posted just fine.

    Between errands.  I posted two comments there after responding in this thread.  “Mule” is just text to create a comment or post, which can then be edited.  It might as well say “placeholder”.  Anyway, I’ll go see how it’s shaping up.

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  7. Haakon Dahl:
    Anyway, I’ll go see how it’s shaping up.

    OK, what is happening is that Akismet (an anti-spam “service” [in the barnyard sense of the word] run by WordPress with the fine sense of quality you’d expect from their main product) is, for some inexplicable reason, flagging the post in the group as spam.  Now this shouldn’t be happening under any circumstances, because I thought I had found and fixed every place where an Akismet check is made and bypass it if the author has been a member of the site for 7 days or more.  Well, it appears I must have missed one (or more) buried in the steaming guts of BuddyPress.  I’ll bet that wherever it is, it only checks new posts and doesn’t re-check posts after you’ve edited them, which is why the “Mule” trick works.  (Recall that in standard BuddyPress you can’t edit posts and comments in groups once posted.  The ability to do that is provided by a plug-in plus Ratburger-developed local code, which probably doesn’t get Akismet into the loop.)

    I will have to dig into this pile of pony poop and find out where Akismet splicing itself into the loop.  The thing is about WordPress, no matter how long you dig, there’s never a pony in there.

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  8. Okay, the comment seems to stick now. It’s as close as I can get it to the original text (pasted from a different computer).  Right now, I cannot reproduce the problem.  Looks like I’ll just have to accept success 🙁

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  9. Heh.  I’m with you on the Pony thing.  BuddyPress did not play nicely with the User Permissions plugin I was using “over there”, and developed permissions leaks.  Which is amazing, because every element in the stack is well-capable of being secured.

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  10. I have just implemented local code which disables Akismet spam checking for posts and comments in groups made by members who accounts were created seven or more days ago.  We already do this for main posts and comments on them, but I missed the place in BuddyPress where it was passing group posts to Akismet, bypassing the main place WordPress does it.

    That’s the thing about WordPress: if there’s a central function which you’d expect is called whenever something is done, you can bet there are three or four other places duplicate code does the same thing on its own without calling the existing function just to make the code less robust, maintainable, and comprehensible.  Having been fooled twice before, I have little confidence I’ve found every place Akismet can get into the act, but at least I’ve fixed the one which burned this post today.

    Full details will be in tonight’s Updates Group post.

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  11. These click-bait headlines have become the norm. It’s almost as if physicists were training to be used-car salesmen. Get your backward light. Act now, while supplies last. The “slow light” flimflammers were not even the first. Earlier, and somewhat more obscure, were the guys hawking Bessel beams: supposedly a way to beat diffraction. The Wikipedia page even claims “A true Bessel beam is non-diffractive.” This is an abuse of the language but off topic so I won’t dwell on it.

    The superluminal and backward light hype relies on anomalous dispersion, which simply means that the refractive index increases for longer wavelengths, dn/dλ>0.* This makes the group velocity do weird things. Normally, group velocity is a useful indicator of the propagation speed of signals. But, as the Wikipedia article notes,

    When the dispersion is anomalous, however, group velocity is no longer an indicator of signal velocity. Instead, a signal travels at the speed of the wavefront, which is c irrespective of the index of refraction. Recently, it has become possible to create gases in which the group velocity is not only larger than the speed of light, but even negative. In these cases, a pulse can appear to exit a medium before it enters. Even in these cases, however, a signal travels at, or less than, the speed of light, as demonstrated by Stenner, et al.

    In other words, it don’t mean a thing if it ain’t got that swing.

    Anomalous dispersion is hardly new. As it happens, it’s the basis of the “hook method” of spectroscopy invented by D.S. Rozhdestvensky, a pre-revolution Russian spectroscopist. This method played an important role in my thesis work. Since the method was invented by a Russian, my research group celebrated each member’s first results with vodka and caviar. After my “first light” party, I went back to the lab to finish up a few things, having first consumed a few shots. The story of what happened next I’ll leave for another time. In short, don’t drink and develop.

    *n=refractive index; λ=wavelength

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