knutsen@sri-unix.ARPA (07/02/85)
From: knutsen (Andrew Knutsen) The Michelson Morley experiment showed that the speed of light is independent of direction. If the influence was being transmitted thru a medium, this would only happen if the source were at rest with respect to the medium. Since the earth cannot at all times be at rest with respect to such a medium (due to its rotations and orbits), MM called the aether into question and was one of the stepping-stones leading to special relativity. The speed of light is slowed in glass because it is absorbed and re-emitted by the glass atoms. No such thing seems to happen in a vacuum. Andrew
infinity%udel-cc-vax2.delaware@udel-louie.ARPA (07/02/85)
From: ALBERS <infinity%udel-cc-vax2.delaware@udel-louie.ARPA> The speed of light is constant? oh, I was under the impression that it changed velocity in substances such as glass, etc. If it did change velocity in such substances why wouldn't it change velocity in a higher density of Ether? Why wouldn't this change in velocity be seen as a 'bending' of light? much as light 'bends' in glass or water. Eric
fred@mnetor.UUCP (Fred Williams) (07/04/85)
In article <344@sri-arpa.ARPA> infinity%udel-cc-vax2.delaware@udel-louie.ARPA writes: > >The speed of light is constant? oh, I was under the impression that >it changed velocity in substances such as glass, etc. If it did change >velocity in such substances why wouldn't it change velocity in a higher >density of Ether? Why wouldn't this change in velocity be seen as a >'bending' of light? much as light 'bends' in glass or water. > > Eric The speed of light in a vacuum is constant. In a transparent material medium light is absorbed by atoms in its path. The time taken for an atom to become excited, (an electron pushed to a higher level), and then re-emit the photon is what "slows" the effective velocity of light in these substances. Maxwell's equations still hold in the empty space between the molocules, and the speed of light is invariant. Cheers, Fred Williams
pmk@prometheus.UUCP (Paul M Koloc) (07/08/85)
> In article <344@sri-arpa.ARPA> infinity%udel-cc-vax2.delaware@udel-louie.ARPA writes: > > > >The speed of light is constant? oh, I was under the impression that > >it changed velocity in substances such as glass, etc. > > Eric > > The speed of light in a vacuum is constant. In a transparent > material medium light is absorbed by atoms in its path. .. .. ... > Maxwell's equations still hold in the empty space between > the molocules, and the speed of light is invariant. > Cheers, Fred Williams The speed of light is a constant in vacuum at given gravitational field density. In general :-) it speeds up infinitely in a void where no matter exists (gets lost). Or another way of looking at it is that the photon wave length goes to infinity as the background gravity field goes to zero. Or another way of thinking about it is the the framing rate (quantized time) goes to infinity. For people living at sea level it (the speed of light) even varies a little because of the tide and the moon. So remember the laws of physics aren't LAW they are consensus guesses OR consensus convention, because otherwise things get complicated. In fact it kind of looks like gravity acts like it has some of the character- istics fantasized for an ether. The ether was kind of a neat idea because it made things like sound waves and light waves a lot more analogous. That is aEther would be a sort of gas like medium for the transmission of light. Gravity is grainy. But grains of what? Well that's another story for yet another episode in this saga of Reality vs Physics. Who will win?? Paul +-------------------------------------------------------+--------+ | pmk@prometheus: (301) 445-1075 | FUSION | | Prometheus II Ltd., College Park, MD 20740-0222 | this | | ..!{umcp-cs,seismo}!prometh!pmk | decade | +-------------------------------------------------------+--------+
claus@inuxd.UUCP (David Claus) (07/08/85)
The speed of light is not always constant. Einstein assumed that the speed of light was constant through any round trip. The speed of light through one leg of that trip can be greater than the speed through another leg. Take for example a light pulse being sent from the earth to the moon and back. Light will travel faster on the way back than on the way there because of gravity effects. Does general relativity take this into account somehow? It is proven that gravity bends light waves (through sun eclipse experiments) so why shouldn't gravity also increase the speed of the light wave? Has there been an experiment that has measured the speed of light during a one way trip through some gravitational potential? Most measurements I've heard of involve the reflection back and forth of a light wave here on earth. Can anyone explain this to me. Dave Claus AT&T/Indy
tan@ihlpg.UUCP (Bill Tanenbaum - AT&T Bell Labs - Naperville IL) (07/09/85)
> The speed of light is not always constant. Einstein assumed that > the speed of light was constant through any round trip. The > speed of light through one leg of that trip can be greater than > the speed through another leg. > > Take for example a light pulse being sent from the earth to the moon > and back. Light will travel faster on the way back than on the way > there because of gravity effects. Does general relativity take this > into account somehow? It is proven that gravity bends light waves > (through sun eclipse experiments) so why shouldn't gravity also increase > the speed of the light wave? Has there been an experiment that has > measured the speed of light during a one way trip through some > gravitational potential? Most measurements I've heard of involve > the reflection back and forth of a light wave here on earth. > > Can anyone explain this to me. > > Dave Claus You are incorrect in several respects. The speed of light in vacuum IS constant, i. e. the same to all observers. Light traveling from the earth to the moon is red-shifted due to the difference in gravitational potential, and light travelling from the earth to the moon is blue-shifted for the same reason. The travel times, however, are frequency independent (assuming transmission in vacuum) and the same in both directions. General relativity does account for the frequency shifting. The answer to your question about the experiment is YES. -- Bill Tanenbaum - AT&T Bell Labs - Naperville IL ihnp4!ihlpg!tan
tan@ihlpg.UUCP (Bill Tanenbaum - AT&T Bell Labs - Naperville IL) (07/09/85)
> You are incorrect in several respects. The speed of light in vacuum IS > constant, i. e. the same to all observers. Light traveling from the earth > to the moon is red-shifted due to the difference in gravitational potential, > and light travelling from the earth to the moon is blue-shifted for the ^^^^^^^^^^^^^^^^^ > same reason. The travel times, however, are frequency independent (assuming > transmission in vacuum) and the same in both directions. General relativity > does account for the frequency shifting. Whoops. that should have been moon to the earth. Sorry. -- Bill Tanenbaum - AT&T Bell Labs - Naperville IL ihnp4!ihlpg!tan
tan@ihlpg.UUCP (Bill Tanenbaum - AT&T Bell Labs - Naperville IL) (07/09/85)
> The speed of light is a constant in vacuum at given gravitational field density. > In general :-) it speeds up infinitely in a void where no matter exists > (gets lost). WRONG: The speed of light is independent of the gravitational field density. > Or another way of looking at it is that the photon wave length > goes to infinity as the background gravity field goes to zero. Or another > way of thinking about it is the the framing rate (quantized time) goes to > infinity. WRONG AGAIN: In the absence of a gravitational field, the photon wave length is also constant. > For people living at sea level it (the speed of light) even varies a little > because of the tide and the moon. WRONG AGAIN: It does not. > So remember the laws of physics aren't > LAW they are consensus guesses OR consensus convention, because otherwise > things get complicated. > > In fact it kind of looks like gravity acts like it has some of the character- > istics fantasized for an ether. The ether was kind of a neat idea because it > made things like sound waves and light waves a lot more analogous. > > That is aEther would be a sort of gas like medium for the transmission of > light. The above statements have no well-defined physical content. > Gravity is grainy. But grains of what? Well that's another story for > yet another episode in this saga of Reality vs Physics. Who will win?? > Paul [Koloc] I suggest that you start your own private newsgroup net.Reality and keep this garbage out of net.physics. -- Bill Tanenbaum - AT&T Bell Labs - Naperville IL ihnp4!ihlpg!tan
matt@oddjob.UUCP (Matt Crawford) (07/10/85)
In article <151@prometheus.UUCP> Paul M Koloc writes some utter gibberish which is appended to this article for the benefit(?) of those who want to refresh their memories. He is far from the first to contribute such nonsense to net.physics. Does anyone else think we ought to try to do something about this? People, let's get serious. This newsgroup is supposed to be for physics, not for sf-lovers, flat-earthers, psychic dabblers or religious debaters. A few philosophical questions in this group are perfectly fine by me, and questions from the less physics- knowledgeable are welcome, but this spouting of total nonsense is extremely annoying to me. There may be innocent readers out there who believe that articles such as the one below actually mean something. I have a folder full of similar nonsense which I have received over the years via US mail. Some of it is printed on heavy glossy paper with pretty letterheads and photos of "experimental equipment", but it is all just as meaningless as the sample below. How can we keep the standards of net.physics up? Can system administrators be expected to squelch their users? Should we all have our favorite newsreading program just kill articles from certain people and pretend that the problem has gone away? Certainly some crackpots and fringies will holler that the "scientific establishment" is trying to "protect itself from creative non-members", but such protestations are not new. Suggestions? _____________________________________________________ Matt University crawford@anl-mcs.arpa Crawford of Chicago ihnp4!oddjob!matt ================= enclosure copied From: pmk@prometheus.UUCP (Paul M Koloc) >The speed of light is a constant in vacuum at given gravitational field density. >In general :-) it speeds up infinitely in a void where no matter exists >(gets lost). Or another way of looking at it is that the photon wave length >goes to infinity as the background gravity field goes to zero. Or another >way of thinking about it is the the framing rate (quantized time) goes to >infinity. > >For people living at sea level it (the speed of light) even varies a little >because of the tide and the moon. So remember the laws of physics aren't >LAW they are consensus guesses OR consensus convention, because otherwise >things get complicated. > >In fact it kind of looks like gravity acts like it has some of the character- >istics fantasized for an ether. The ether was kind of a neat idea because it >made things like sound waves and light waves a lot more analogous. > >That is aEther would be a sort of gas like medium for the transmission of >light. > >Gravity is grainy. But grains of what? Well that's another story for >yet another episode in this saga of Reality vs Physics. Who will win?? > Paul >+-------------------------------------------------------+--------+ >| pmk@prometheus: (301) 445-1075 | FUSION | >| Prometheus II Ltd., College Park, MD 20740-0222 | this | >| ..!{umcp-cs,seismo}!prometh!pmk | decade | >+-------------------------------------------------------+--------+
AI.Mayank@MCC.ARPA (07/10/85)
From: Mayank Prakash <AI.Mayank@MCC.ARPA> >From: ihnp4!inuxc!inuxd!claus@UCB-Vax.ARPA (David Claus) >Subject: Re: Light >Article-I.D.: <778@inuxd.UUCP> >In-Reply-To: Article(s) <345@sri-arpa.ARPA> > >The speed of light is not always constant. Einstein assumed that >the speed of light was constant through any round trip. The >speed of light through one leg of that trip can be greater than >the speed through another leg. > >Take for example a light pulse being sent from the earth to the moon >and back. Light will travel faster on the way back than on the way >there because of gravity effects. Does general relativity take this >into account somehow? It is proven that gravity bends light waves >(through sun eclipse experiments) so why shouldn't gravity also increase >the speed of the light wave? Has there been an experiment that has >measured the speed of light during a one way trip through some >gravitational potential? Most measurements I've heard of involve >the reflection back and forth of a light wave here on earth. > >Can anyone explain this to me. > >Dave Claus >AT&T/Indy According to general relativity, the presence of mass curves space-time around it. That is, it causes the notions of length and time to alter from point to point in such a way that the speed of light is the same at each point, when measured in terms of the length and time apropriate for that point. The average speed of light, say between moon and earth may be different from c, but measuring that difference would be beyond the current technology, I would think. Remember that the gravitational fields of the earth and moon are extremely weak, as is for that matter, that of the sun, in terms of the curvature produced by them. That is the reason why Newton's Law of gravitation is almost all you need to describe the solar system. (To give you an idea of its weakness, a ray of light just grazing the sun's surface is bent by a measly 1.75 seconds of an arc. The only measurable deviation from the Newton's law is the perihelion advance of Mercury's orbit at the rate of a few seconds of an arc per century. The same effect for the other (more distant) planets is far too small to be measured.) - mayank. -------
fred@mnetor.UUCP (Fred Williams) (07/11/85)
In article <151@prometheus.UUCP> pmk@prometheus.UUCP (Paul M Koloc) writes: >> >> The speed of light in a vacuum is constant. In a transparent >> material medium light is absorbed by atoms in its path. .. .. ... >> Maxwell's equations still hold in the empty space between >> the molocules, and the speed of light is invariant. >> Cheers, Fred Williams > >The speed of light is a constant in vacuum at given gravitational field density. >In general :-) it speeds up infinitely in a void where no matter exists >(gets lost). Or another way of looking at it is that the photon wave length >goes to infinity as the background gravity field goes to zero. Or another >way of thinking about it is the the framing rate (quantized time) goes to >infinity. > Exactly how would you go about measuring the speed of light with the background gravity field at zero? You would have to have an empty universe. How big would it be? How fast would time be flowing? There is very little that can be defined. >For people living at sea level it (the speed of light) even varies a little >because of the tide and the moon. So remember the laws of physics aren't >LAW they are consensus guesses OR consensus convention, because otherwise >things get complicated. > No one has ever detected variation in the speed of light. True, even relativity is still called a "theory" despite all the evidence to support it. Scientists are rather conservative about things like this. >In fact it kind of looks like gravity acts like it has some of the character- >Gravity is grainy. But grains of what? Well that's another story for >yet another episode in this saga of Reality vs Physics. Who will win?? > Paul What do you mean, "grainy"?!?! You're not one of these people who believes gravity is electromagnetic are you? If that were so there would be no gravity around a black hole. Cheers, Fred Williams
mcgeer%ucbkim%Berkeley@sri-unix.ARPA (07/13/85)
From: Rick McGeer <mcgeer%ucbkim@Berkeley> From: ihnp4!inuxc!inuxd!claus@BERKELEY (David Claus) Subject: Re: Light Article-I.D.: <778@inuxd.UUCP> In-Reply-To: Article(s) <345@sri-arpa.ARPA> The speed of light is not always constant. Einstein assumed that the speed of light was constant through any round trip. The speed of light through one leg of that trip can be greater than the speed through another leg. Take for example a light pulse being sent from the earth to the moon and back. Light will travel faster on the way back than on the way there because of gravity effects. Does general relativity take this into account somehow? It is proven that gravity bends light waves (through sun eclipse experiments) so why shouldn't gravity also increase the speed of the light wave? Has there been an experiment that has measured the speed of light during a one way trip through some gravitational potential? Most measurements I've heard of involve the reflection back and forth of a light wave here on earth. Can anyone explain this to me. Dave Claus AT&T/Indy Gravity won't accelerate a light wave. *Nothing* accelerates a light wave in a vacuum. Instead, the wavelength is affected, in much the same way that the wavelength of light varies as the observer's velocity wrt to the source varies. Rick.
gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (07/14/85)
> True, even relativity is still called a "theory" despite > all the evidence to support it. Scientists are rather conservative > about things like this. Actually, "theory" in this context does not imply "possibly wrong". It is just a coherent explanation subject to several technical constraints that I won't bore you with. A "theory" in this sense may even be provable yet still be called a "theory". This usage is NOT the same as when someone says "it's only a theory". > You're not one of these people who believes gravity is > electromagnetic are you? If that were so there would be no gravity > around a black hole. That's no counterargument. "Black holes" have not been conclusively demonstrated to exist, let alone gravitate. All we "know" about them so far is a bunch of theoretical speculation..
gwyn@BRL.ARPA (07/15/85)
From: Doug Gwyn (VLD/VMB) <gwyn@BRL.ARPA> Gravity doesn't "bend light waves" according to general relativity; it warps the structure of spacetime. Light follows a null geodesic (think of it as the "shortest path") in all cases, so that it appears to take a bent path to an observer who does not take the space-time curvature into account. It is really meaningless to question whether the "speed of light is constant" without describing how units of space and time measurement are to be determined, since speed will be measured in such units. The concept of "null geodesic" is invariant with respect to any choice of units.
tan@ihlpg.UUCP (Bill Tanenbaum - AT&T Bell Labs - Naperville IL) (07/15/85)
> From: Doug Gwyn (VLD/VMB) <gwyn@BRL.ARPA> > > Gravity doesn't "bend light waves" according to general relativity; > it warps the structure of spacetime. Light follows a null > geodesic (think of it as the "shortest path") in all cases, > so that it appears to take a bent path to an observer who does > not take the space-time curvature into account. > > It is really meaningless to question whether the "speed of light > is constant" without describing how units of space and time > measurement are to be determined, since speed will be measured in > such units. The concept of "null geodesic" is invariant with > respect to any choice of units. The statement "speed of light is constant" is meaningful and correct if the speed is always measured locally. The curvature of space-time can be ignored if the domain is small enough, i.e. space-time is locally flat. It does not matter what units we use. The magnitude of a physical quantity does not depend on the units of measurement. -- Bill Tanenbaum - AT&T Bell Labs - Naperville IL ihnp4!ihlpg!tan
leon@hhb.UUCP (Leon Gordon) (07/17/85)
just a comment on the deflection of light by gravity:
1) light is deflected by a grav field in the same sense that
particles in free fall are - one can take the point of view
that there is a grav. interaction, or one can take the point
of view that there is no force, but rather an altered geometry.
I agree that the latter view is more appropriate to a relativistic
analysis; I just want to point out that the effect on a beam of
light is conceptually similar to the effect on a stream of particles.
2) The old classic by Eddington (Relativity, Thermodynamics, and
Cosmology) contains a simple relativistic calculation of the
deflection of a pencil of light by a gravitational field.
Interestingly enough, light is deflected twice as much as particles
of the same energy content. This is because of the radiation
pressure terms in the stress-energy tensor which are negligable
for (classical) particles.
leon
{decvax,ihnp4,allegra}!philabs!hhb!leonart@denelvx.UUCP (Art Coleman) (07/18/85)
>From: Rick McGeer <mcgeer%ucbkim@Berkeley> >> >> From: ihnp4!inuxc!inuxd!claus@BERKELEY (David Claus) >> >> The speed of light is not always constant. Einstein assumed that >> the speed of light was constant through any round trip. The >> speed of light through one leg of that trip can be greater than >> the speed through another leg. >> >> Take for example a light pulse being sent from the earth to the moon >> and back. Light will travel faster on the way back than on the way >> there because of gravity effects. Does general relativity take this >> into account somehow? It is proven that gravity bends light waves >> (through sun eclipse experiments) so why shouldn't gravity also increase >> the speed of the light wave? Has there been an experiment that has > >Gravity won't accelerate a light wave. *Nothing* accelerates a light wave in a >vacuum. Instead, the wavelength is affected, in much the same way that the >wavelength of light varies as the observer's velocity wrt to the source varies. > > Rick. Does this mean that light DOES excape a black hole, but at a wavelength (IE: frequency?) so high or low as to be undetectable? Does QM maintain that this wavelength is infinately long with the resulting frequency of 0? In that case, what happens to the photon? energy? @ = Art Coleman - Manager Operating Systems Software Development Denelcor Inc. - 17000 E. Ohio Pl. - Aurora Colo 80017 303-337-7900 ..!hplabs!hao!{nbires|csu-cs}!denelcor!art or ..!brl-bmd!denelcor!art
matt@oddjob.UUCP (Matt Crawford) (07/24/85)
In article <102@denelvx.UUCP> art@denelvx.UUCP (Art Coleman) writes: > >Does this mean that light DOES excape a black hole, but at a wavelength >(IE: frequency?) so high or low as to be undetectable? No, light does not escape. In the interior of a black hole, space is curved in such a manner that all directions lead inward toward the center. Light still travels 'at the speed of light', but no matter which direction it goes, its path leads inward. _____________________________________________________ Matt University crawford@anl-mcs.arpa Crawford of Chicago ihnp4!oddjob!matt