If ether really existed, wouldn’t it create friction causing the earth (and all heavenily bodies, really) to have stopped spinning long ago? IIRC, it is said Einstein could not directly prove that ether did not exist because all such experiments could not discern if the ether moved with us; hence, no apparent motion. Ether was only proven to not exist by indirect means.
So, wouldn’t ether create some friction? Was that ever considered back then?
Ether just has to be a medium that carries light waves, and doesn’t have to have any other particular properties (such as causing friction to bodies that move through it). From what we know of the behaviour of light waves, ether would definitely not have frictional effects on light (because light doesn’t slow down etc.), so why would it have to have frictional effects on anything else?
I’m not sure that you really can prove that ether doesn’t exist. You can just prove that it doesn’t have any of the properties that you’d expect matter to have (apart from transmitting light). If it doesn’t have any properties, and you can construct theories that work with light going through empty space, why do you need to hypothesise an ether?
It’s worth emphasising that were over two centuries of serious theorising about different types of aether. People used the basic idea for different purposes and the different models often had very different properties that they ascribed to their aether. Some people thought that the aether would interact with the Earth and other planets and came up with different ways this could happen. Others thought that there wouldn’t be any such interaction, perhaps because the aether could pass straight through otherwise seemingly solid matter.
In all these arguments, everybody was aware that friction between planets and the aether could easily cause them to spiral down into the Sun. That was a constraint on all the models.
When it comes to the situation around 1905, by then it was agreed that, whatever it’s properties, the aether had to have very, very extreme properties. But there was still a great deal of diversity amongst the ideas on the table.
One class of the theories involved the Earth dragging along a “shell” of aether as it passed through it. But one could then assume that the aether itself was some sort of frictionless fluid, so that there was no friction between the Earth+shell and the surrounding aether.
That was roughly what Michelson thought and used as an explanation for his initial experimental results. To test this idea, he thus repeated that initial version at different altitudes; perhaps mountaintops were high enough that they poked up through the shell into the aether that wasn’t accompanying the Earth.
As usual, there’s the bad habit textbooks and other accounts have of regarding the Michelson-Morley experiment as a single experimentum crucis. Even looking at it in isolation, there were a series of versions of it as Michelson tried to test different ways the aether involved might be dragged along with the Earth.
First of all, the ether was proposed and widely accepted as an explanation for the medium enabling the transmission of light as a wave. Previously, it was asserted by no less an authority than Sir Issac Newton that light was"corpuscular" or particulate in nature, though even Newton acknowledged that light did appear to have some effects that were best explained by modulated waves. He rationalized this by hypothesizing that the wave effects were a result of interaction between light particles and “heat radiations”, which was, given the state of knowledge at the time, a perfectly reasonable (if improperly dichotomized) explanation.
Later observations and experiments in astronomy and optics demonstrated that light does demonstrate obviously wavelike behavior in diffraction and refraction. The problem with this is that waves aren’t physical objects; they’re disturbances in some medium. Natural philosophers and astronomers already knew that space was a vacuum, and in any case, light was able to propagate through artificial vacuums in a laboratory, so it was clearly not the case that a mechanical medium was required to permit the transfer of light waves. The obvious solution was to conjecture a non-material medium, a “luminiferous aether” (I personally enjoy the anachronistic spelling of the term) which was invisible, completely permeable to solids, liquids, and gases, and is chemically inert, interacting only with light “packets”. This theory was further bolstered by the discovery of Maxwell, Heaviside, and Gibbs (it’s not really clear which of them first came to the conclusion) that light propagates exclusively at one speed, c, regardless of frequency or intensity. This appeared to demand some kind of fixed, stationary medium which regulated the velocity of light waves.
The theory was soundly accepted until the now-famous and paradigm-uprooting experiments of Michaelson and Morley, who demonstrated that, despite the velocity of the Earth in its orbit about the Sun, the velocity of the Sun with respect to the galaxy, and so forth, all in motion relative to the (presumably) fixed background of the aether, there was no addition or subtraction of velocities to the speed of light; light appeared to be moving at c without modification regardless of what direction you viewed it at. The Michaelson-Morley experiments, which, as bonzer points out wasn’t a single “Eureka!” moment but rather a long series of experimental refinements, weren’t intended to disprove the existence of the aether at all but rather to establish the Earth’s velocity relative to it, and the work was continued by them and others to further refine the measurements in the assumption that the equipment was simply not sensitive enough.
Eventually, though, it became obvious (to even the most dimwitted individual…who holds an advanced degree in hyperbolic topology, hur-hey) that the equipment and method were not at fault and that something was amiss with the aether theory. A number of attempts were made to patch the theory in order to make it coherent with the observations, including the attempt to rationalize the results as an indication that the Earth was somehow dragging the aether along with it. Other theories (which would no doubt be regarded as tin-foil-hatisms now but were at least rationally speculative at that time) were advanced but none satisfied both the wave phenomena, the particulate behavior, and the speed invariance of light. The Wikipedia article on the MM experiment states that Ernst Mach “Ernst Mach was among the first physicists to suggest that the experiment actually amounted to a disproof of the aether theory,” but in fact I think that there were a substantial number of physicists (particularly young turks who were tired of listening to the old farts drone on about how they already figured it all out in their day) who considered the repeated failure to locate the medium to be a harbinger for an original explanation.
Einstein’s Special Theory of Relativity established a rationale for the invariance of the velocity of light while dispensing with any medium and General Relativity accounted for its behavior with respect to masses and gravitation. His less celebrated but just as innovative work on the photoelectric effect established that light did, in fact, have properties of both a wave (diffraction, refraction) and a particle (discrete energy levels, not requiring a medium), leading to the birth of quantum mechanics.
Light is often described today, confusingly and perhaps obtusely, as being both a particle and a wave, which is a fundamentally incorrect; light can be modeled (in some situations) as a particle and (in others) as a wave, but never both simultaneously. Instead, like all fundamental particles, it is a field which which interacts with other fields, which begs the question of it being being a field in what? It may be that light does require some kind of underlying medium for transmission and simply appears (in the “classical” world) as a blip on the surface of space, just as a wavelet in the ocean appears to be a line moving on to of the water, but such a theory would have to account for the invariance of velocity as established by SR and GR, or otherwise overthrow relativity entirely and replace it with something even more bizarre.
In short, although we know today that the traditional (and, in its day, quite reasonable) explanation of the luminiferous aether is incompatible with our understanding of relativity; we do not know with any certainty, however, how light goes from Point A to Point B, like a baseball from the pitcher to the catcher’s mitt, and yet can suddenly disappear into the mitt and then spontaneously re-emit itself as a cricket ball. We have a model that accounts for all the waypoints, but it doesn’t explain what the ball is made of. There are numerous speculations, from the M-Theories to quantum loop gravity, none of which entirely satisfy General Relativity and all of which are probably mostly wrong, though each may possibly offer some clue as to which part of the elephant the observer has his hand upon. In this way they are reminiscent of the theories which sought to replace aether theory; that serves as both a caution to those who would insist upon the validity of their unsubstantiated claims and a stimulation to advance and further refine new fundamental theories.
Great explanation, Stranger, and the best I’ve read.
But all that is based on the assumption that light has “speed”. Are all scientists in agreement with it ? I would like to know whether there are any dissidents.
(Sorry for hijacking. Just want to avoid starting a thread)
I once ran across an ~1890’s physics text which described subatomic particles as “vortex rings of the luminiferous aether.” Given the state of subatomic physics at the time, it must have been quite an advanced discussion. Seeing it a hundred years later really emphasized how far we’ve come since those days.
Well, light definitely has a finite speed, which you can verify by making an overseas call. It is widely (virtually universally) accepted that the speed of light is invariant; this is a fundamental result of both special relativity and Maxwell’s Equations. There are some hypothetical situations in which light can make a timelike path through space in which its transit from Point A to Point B takes less time than (B-A)/c but these generally require some kind of massive gravitational effects which, while verifiable to a point (e.g. frame dragging around our rotating Sun) aren’t significant enough to be practical to exploit as some kind of time machine or superluminal device, and indeed, astrophysicists and relativity physicists assume some kind of “Law of Universal Censorship” to prevent all sorts of disturbing phenomena from taking place, what with matter and energy spontaneously disappearing and reappearing, not to mention your dead Aunt Lucy suddenly popping up at your child’s first Communion and so forth. That would be creepy, and to no one less your local University’s Physics Department, unless it turns out that she wasn’t actually dead but was merely very tired, upon which it reverts to the pervue of the Cognitive Science program.
But there is no physical reason such paths can’t exist, and many reputible relativity researchers (or, at least as reputable as a relativity physicist could be, as it is hard to take seriously someone who eschews the attractions of the material world for a basement office and while unquestionably end up his career mumbling incoherently about singular null hypersurfacees and nitpicking the pseudoscience of Star Trek[sup]1[/sup]) have, strictly as a hobby of course, gone about constructing mathematical models of causality-violating timelike curves around rotating black holes and so forth. It’s all in good fun until someone puts an Lorentzian manifold out with a sharp singularity.
Quantum dynamicists, on the other hand, who’ll allow a particle to leap instantaneously to any arbitrary position in the universe, don’t worry themselves about causality. “It’ll all average out in the wash,” they claim. But then, they’re even less reputable than relativity researchers, and usually drink their gin in shots.
There are some speculations that, while invariant for any time t, the univerisal constant of light (along with other constants) may vary over time. This does provide for some interesting explainations to cosmological phenomena but is presently considered to be about as substantiated as rumors of Samual Clemens’ metaphorical expiration, and the proponents of said claims are held in even lower regard than quantum mechanics researchers, drinking, as they do, domestic rail vodka over ice.
That it did, and if merit alone were the exclusive criteria by which the Nobel Committee made its awards he’d probably be hanging a pair of them (er, of medals, hanging over his desk, of course). However, he is far more widely known today for his work in relativity than for being the spirtual father of quantum mechanics; perhaps that is unsurprising given his stated discomfort with many of the conclusions of QM. Ask the [strikethrough]random man on the street[/strikethrough]student in an introductory Modern Physics course what Big Al is most noted for and they’ll probably respond with some shaggy dog story about twin brothers and rocketships.
My textbook for first semester modern physics, for instance (Beiser’s Concepts of Modern Physics, Fourth Edition, which was at the time the textbook in use at such luminary institutions on the cutting edge of physics research as MIT, UC-Berkeley, and University of Missouri-Rolla[sup]2[/sup]) gives our barber’s worst nightmare three largish paragraphs of biography, taking up the bulk of a page, in which he gets exactly one sentance devoted to his work and publication on the photoelectric effect. His work on Brownian motion actually gets more verbage. His work on SR and GR, however, get the remainder of that paragraph and the bulk of the next. This represents the sum total of what was presented to me curricularly about Sleepy E (reportedly he used to fall asleep in colloquia) in the course of my aborted education in physics, and I’d guess that most engineering and science students, whose interest in Bert extends no further than a t-shirt image of him with some witty caption promoting a malt-based alcoholic beverage product. At least he gets some coverage; De Broglie gets a paltry four sentances; Maxwell and Planck get slightly more allowance; Feynman’s entry highlights his bongo playing and safecracking activities in more detail than his offerings to QED; and Murray Gell-Mann, the progenitor of the quark, has no entry at all, despite being a Nobel Laureate of 25 years (as of the printing of the book) standing.
Would it really be so difficult to include a freestanding chapter on the developments and personalities of 20th Century physics, just for reference? ::sigh::
[sup]1[/sup] Just kidding, there. I don’t want Chronos to come and beat me up.
[sup]2[/sup] Really just kidding, there. T’was not the most celebrated of departments, but it was really, really cheaper than the out of state or private institutions who failed to offer any fiscal assistance in my drive to be an unemployable Ph.D.
I think you’re right historically. Long term memory isn’t the most reliable source of information. However, in digging through this search: [“vortex rings” ether](vortex rings" ether), it seems Lord Kelvin did propose a vortex ring as a model for the electron.
There’s a lot of odd results in that search, and much woo woo. However, this historical illustration on the generation of vortex rings is pretty nice. The caption even mentions frictionless ether.
First, I’ve never noticed the spelling difference between ether and aether. I will look into this. For now, I will spell it as “ether”. (Then, we can argue over “gage”!?!)
Second, for those posting above who simply claim ether was a medium for the propogation of light waves, you’re failing to miss WHY this would be. Like sound waves, it was reasoned that such a medium would require molecules. Likewise, ether (and I will still spell it as-is) would have to be made of molecules for the propogation of light. Molecules would create friction. The friction would cause an appreciable effect on the earth’s rotation - and revolution, for that matter.
Just defending my position having glanced over the replies. I will check back shortly! - Jinx
Ok… taking more time to read the details from “Stranger On a Train” above, the answer is clear that ether (and the spelling can vary) would only interact with light for the propogation of light waves only.
“Stranger” explains all…thanks, Stranger…and, don’t be such a Stranger!