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Thread: Speed of light

  1. #1
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    Speed of light

    Ok I have seen a few articles now, on Facebook though about how data from the 1987 supernova says that we might be wrong about the consistency of the speed of light.
    I'd love to here what others think about this


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  2. #2
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    Greetings,

    Quote Originally Posted by mikeEZfoSheezy View Post
    Ok I have seen a few articles now, on Facebook though about how data from the 1987 supernova says that we might be wrong about the consistency of the speed of light.
    Two comments seem appropriate.

    First, you might want to read the Neutrino emissions section of the Wikipedia article on SN 1987A. It discusses the differences between the physical mechanisms and the relevant dynamics that generate the neutrinos and the visible photons.

    Second, there are sources of scientific information that have slightly better reputations than Facebook.

    Best regards,
    ES

  3. #3
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    I was just curious about other thoughts cause I seen the articles being posted on many different astronomy and science Facebook pages and websites


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    This is a problem about relying on pop-sci and pop-culture sources for science. Roll the dice and I'd say there is a better then 50% chance that, not only did they get something wrong but, they got something grossly wrong. It is sad because there is a lot of exciting things going on in science without, at best, extrapolating a story far beyond what the science says.

    There is a lot of interesting science coming out of supernova research. We are finding out there are many more variations then just the 2 we normally address. A pop-sci article is more likely to run with that type of data to say something like "New supernova data disproves the big bang" then "Variations in supernova observation indicate previously unknown dynamics"

    Finally no one should take it personally when it is pointed out to them that sources like this are not a good source for science info and not provide you with a better explanation.
    This is for a few reasons.
    First is we don't have any idea what exactly these articles you speak of are claiming so it is hard to give you an answer about what is wrong with them.
    Second is stories from sources like this often aren't worth the time to even read. You might think "but it is only one or a few articles". But you are only one of many people that come here with articles from questionable sources.
    Third, such articles often give no source for what they are based off of so not much for people here to work with.

    The articles amount to hand waving and word salad designed to trick and impress readers that aren't educated, either formally or self taught, in a particular domain.
    Things I don't do on face book
    Reply to post that say things along the line of
    "Name a country that does NOT contain the letter A. Bet you can't do it!",
    "8=56, 7=42, 6=30, 5=20, 3=?" this one for multiple reason A) It has been done to death B) those aren't valid math equations. I'd accept f(8)=56 but that would confuse to many people sadly.
    Any math problem that is just testing your 4th grade understanding of order of operations.

    Any posts that ask you to pass them on in general.

    If I see anything interesting on FB I then independently research the claim. Very often the post has got is grossly wrong.
    Last edited by WayneFrancis; 2014-Jun-30 at 01:09 AM.

  5. #5
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    Quote Originally Posted by mikeEZfoSheezy View Post
    Ok I have seen a few articles now, on Facebook though about how data from the 1987 supernova says that we might be wrong about the consistency of the speed of light.
    Without any citation to the actual science, we can only guess what these FB pages are talking about.
    I guess: Apparent correction to the speed of light in a gravitational potential
    Where the author explicitly states that his work is "...presumably nonphysical. Nevertheless, the predicted results are in reasonable agreement with experimental observations from Supernova 1987a.".
    This post at JREF points out the actual error in the paper.
    That that the author (J D Franson) has no published expertise in GR (he is an expert in in optical physics) suggests where the mistake come from.

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    Quote Originally Posted by Reality Check View Post
    Without any citation to the actual science, we can only guess what these FB pages are talking about.
    I guess: Apparent correction to the speed of light in a gravitational potential
    Where the author explicitly states that his work is "...presumably nonphysical. Nevertheless, the predicted results are in reasonable agreement with experimental observations from Supernova 1987a.".
    This post at JREF points out the actual error in the paper.
    That that the author (J D Franson) has no published expertise in GR (he is an expert in in optical physics) suggests where the mistake come from.
    I believe this is in reference to light changing to a massive particle for a moment, which slows it down, and then turns back into light. Therefore the apparent velocity is lower by a fraction of 0.000000003.

    http://phys.org/news/2014-06-physici...r-thought.html

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    Quote Originally Posted by Copernicus View Post
    I believe this is in reference to light changing to a massive particle for a moment, which slows it down, and then turns back into light. Therefore the apparent velocity is lower by a fraction of 0.000000003.

    http://phys.org/news/2014-06-physici...r-thought.html
    That is correct - a photon can change to 2 massive virtual particles for a short time, e.g. a virtual electron and virtual positron. But it is wrong to treat these virtual particles as real particles and plug rest masses into GR.

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    Quote Originally Posted by Reality Check View Post
    That is correct - a photon can change to 2 massive virtual particles for a short time, e.g. a virtual electron and virtual positron. But it is wrong to treat these virtual particles as real particles and plug rest masses into GR.
    I am not sure what you are referring to?

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    I call hogwash! If you want to say the creation and annihilation of virtual pairs slows down light, then you need to accept that it will depend on the energy of the photon. Gamma rays will slow down more than visible photons through this polarization effect. That's been tried, and the effect is amazingly small(if real) compared to what this inferior article claims.

    http://www.skyandtelescope.com/astro...ace-time-foam/

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    This idea requires the existence of space-time foam, which IIRC has not been clearly demonstrated. Also the original article is from 2009, and now it is 2014. I have my reservations since I have heard nothing in the interval. While S&T is orders of magnitude above boob tube et al., they do run an occasional gee whiz piece.
    I'm not a hardnosed mainstreamer; I just like the observations, theories, predictions, and results to match.

    "Mainstream isnít a faith system. It is a verified body of work that must be taken into account if you wish to add to that body of work, or if you want to change the conclusions of that body of work." - korjik

  11. #11
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    Quote Originally Posted by Copernicus View Post
    I am not sure what you are referring to?
    In QM, particles can turn into virtual particle/anti-particle pairs: Virtual particle

    In physics, a virtual particle is a transient fluctuation that exhibits many of the characteristics of an ordinary particle, but that exists for a limited time. The concept of virtual particles arises in perturbation theory of quantum field theory where interactions between ordinary particles are described in terms of exchanges of virtual particles.
    You can think of it as an application of the Heisenberg uncertainty principle for energy and time where the creation of particles for a short enough time is allowed.

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    Quote Originally Posted by Reality Check View Post
    In QM, particles can turn into virtual particle/anti-particle pairs: Virtual particle


    You can think of it as an application of the Heisenberg uncertainty principle for energy and time where the creation of particles for a short enough time is allowed.
    Are you saying the virtual particles can't be treated as real, and the rest masses and relativity can't be used to calculate a reduced velocity of the virtual particles for however long these virtual particles may be in existence.

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    Quote Originally Posted by Copernicus View Post
    Are you saying the virtual particles can't be treated as real, and the rest masses and relativity can't be used to calculate a reduced velocity of the virtual particles for however long these virtual particles may be in existence.
    In short, that is correct. Virtual particles need not respect our precious conservation laws.

    See on shell versus off shell:
    http://en.wikipedia.org/wiki/On_shell_and_off_shell

    Don't feel bad if it makes no sense. I'm a physics major and it's still out of my reach.

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    Virtual particles get many free passes that normal particles don't. They can ignore even the event horizon of a black hole from my understanding.

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    A slightly related blog entry about how even the masses of fundamental particles are not "known"
    The most basic unknowable property of matter
    We can only talk about an average mass for a very short-lived particle like a W-or-Z-boson because the short lifetime gives a wide uncertainly in energy (Heisenberg’s uncertainty principle) and thus the equivalent mass.

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    The description Hawking gave of how particles are emitted
    by a black hole critically requires virtual particles, but does
    not involve those particles crossing the event horizon in the
    upward direction. Pairs of virtual particles supposedly come
    into existence frequently everywhere, and go out of existence
    again before they can have any effect on anything. But near
    the event horizon of a black hole -- ABOVE the horizon -- the
    gravitational gradient can be strong enough that one of the
    virtual pair escapes while the other falls in, and they can't get
    back together before their time is up, so both particles become
    physical. The energy to make them physical came from the
    gravitational field pulling them apart. The one which escapes
    carries away its share of the energy, so the overall mass of
    the black hole is reduced by the mass-energy of the escaping
    particle.

    -- Jeff, in Minneapolis

  17. #17
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    Reality Check,

    That link gave me a page with header and footer, but no body.

    -- Jeff, in Minneapolis

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    Peru, Mexico, Greece - oh, sorry did you don't answer it :-)

  19. #19
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    Quote Originally Posted by Jeff Root View Post
    The description Hawking gave of how particles are emitted
    by a black hole critically requires virtual particles, but does
    not involve those particles crossing the event horizon in the
    upward direction. Pairs of virtual particles supposedly come
    into existence frequently everywhere, and go out of existence
    again before they can have any effect on anything. But near
    the event horizon of a black hole -- ABOVE the horizon -- the
    gravitational gradient can be strong enough that one of the
    virtual pair escapes while the other falls in, and they can't get
    back together before their time is up, so both particles become
    physical. The energy to make them physical came from the
    gravitational field pulling them apart. The one which escapes
    carries away its share of the energy, so the overall mass of
    the black hole is reduced by the mass-energy of the escaping
    particle.

    -- Jeff, in Minneapolis
    I'm not sure if you are addressing what I posted. I was just pointing out that the hypothetical virtual particle the graviton is not limited by the EH and it has been told to me on these forums that other virtual particles aren't under the same constraint as real particles.

  20. #20
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    Apparently I wasn't addressing what you meant. I didn't
    realize you had virtual gravitons in mind. The problem with
    describing the behavior of virtual gravitons is that there
    may be no such thing as gravitons. They're hypothetical.

    -- Jeff, in Minneapolis

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