|
|
| Top of Page | Overview | Home |
Question #2:
In Figure B, the rear flash is moving toward the ground detector and the front flash is moving away from that detector; so, wouldn't the photons from the rear flash have to reach that detector before the ones from the front flash?
That reasoning also makes some intuitive sense, but laboratory studies of binary stars and other moving light sources prove that the motion of a light source will have no measurable affect on the speed of light leaving that source. If each flash in Figure B occurs at the moment the detector on the ground is directly opposite the midpoint of the train, thus halfway between the two light sources, then it has also been fully proven in the laboratory that the light from each flash will reach that detector on the ground at the same time, regardless of the motion of those light sources.
| Top of Page | Overview | Home |
Question #3: If Figure A predicts that the light from each flash will meet at the train detector, and if Figure B predicts that exactly the same light waves will meet at the ground detector --and if the detectors are moving apart during the time the light waves are moving from each flash to each detector, then those would be mutually exclusive predictions and could not both be correct! So, how could both of those predictions be correct?
This may be the most important question to be answered about these deceptively simple findings, so this question will be answered in several different ways:
- Answer to Question #3 in overview
- Answer to #3 in terms of physical laws
- Answer to #3 in terms of relativity theory
- Answer to Question #3 in plain English
Answer to Question #3 in overview It is true that Figure A predicts that the photons from each flash will meet at the train detector and Figure B predicts that the same photons will meet at the ground detector, and since the detectors will be moving apart during the time the photons are moving from each source to each detector, it would seem impossible for both predictions to be correct.
However, if exactly the same events were viewed by an observer riding on one of the photons, which would be simply a different view of these same events, then according to theory, the passage of time for that observer would slow to a stop due to the high velocity of the photons, and although the detectors would be moving apart during the entire time the photons were moving from each flash to each detector, they would not have time to move anywhere (in that observer's view); therefore, that observer would have to see the light from each flash reach each detector simultaneously.
That outcome is counterintuitive, but that is what would actually happen if this experiment were run in a laboratory, so that outcome would clearly not be impossible. In fact, because the laws of physics must be equally valid in all reference frames, that would be the only outcome possible for these events, since it is the only outcome that would be valid in the reference frame of the photons as well as those of both the train and the ground.
Top of Page Return to #3 Home
Answer to Question #3 in terms of physical lawsThe outcome in Figure C is counterintuitive, but intuition has never been reliable for predicting the behavior of light, and it is not needed here. The only events that take place in these figures have been carefully examined and confirmed in the laboratory and those findings now constitute the fully proven empirical laws of light propagation.
In each illustration, only two events occur: A single flash occurs at the front of the train and a single flash occurs at the rear of the train, and each flash occurs at a particular time.
In Figure A, it is stipulated that a photon detector is attached at the center of the train and each flash on the train occurs at the moment that central detector is directly opposite a single reference point on the ground. Figure A essentially summarizes the laboratory findings of Michelson-Morley, which prove that the light from each flash would have to reach that central detector on the train simultaneously, regardless of the motion of the train.
In Figure B, a photon detector is fixed to the ground, and it is stipulated that each flash on the train occurs at the moment the midpoint of the train is directly opposite that detector on the ground, that is, at the moment the ground detector is exactly halfway between those two light sources. This essentially summarizes the laboratory findings of binary stars and other moving light sources, which prove that the light from each flash in Figure B would have to reach the detector on the ground simultaneously, regardless of the motion of those light sources.
Figure C simply combines those two fully confirmed and documented findings from the literature into a single experiment: If a large flashbulb is attached at each end of a long, fast-moving train, and if each flashbulb discharges when a photon detector mounted at the center of the train is located directly opposite a similar detector on the ground, then it has been proven by some of the most carefully confirmed findings in the physics literature that the light from each flash would reach each of those detectors simultaneously.
That conclusion is counterintuitive, but if it were not correct, then some of the most carefully replicated and consistently confirmed findings in all of physics would have to be wrong (the laws of light propagation), and that would be a difficult argument to support.
Top of Page Return to #3 Home
Answer to #3 in terms of relativity theoryIn the original train/lightning thought experiment, which Einstein used to illustrate the first step in the derivation of relativity theory (the relativity of simultaneity theory), it is stipulated that lightning bolts strike the ground at each end of a long, fast-moving train at the moment an observer on the ground next to the train (a man in this example) is located directly opposite a second observer (a woman) seated on the train at its exact center. It is argued (and proven by the Michelson-Morley findings) that the light from each flash would reach the man on the ground simultaneously, since he would be located halfway between those two light sources and not moving relative to them. Therefore, that man would have to conclude that the lightning flashes occurred simultaneously.
Relativity theory then argues, using that same train/lightning thought experiment, that since the woman on the train would be moving toward the front flash and away from the rear flash during the time the photons from each flash were traveling toward her, she would have to encounter the photons from the front flash before the photons from the rear flash by at least some finite amount; therefore (if the woman could not tell that the train was moving), she would have to conclude that the flashes did not occur simultaneously, that the front flash occurred before the rear flash by at least some finite amount.
That is the relativity of simultaneity theory: the theory that the appearance of simultaneous events will vary depending on the relative motion of the observer of those events. As discussed in the Background section, no proof has ever been offered for the central assumption underlying that theory (the assumption that the woman would encounter the photons from the front flash before the photons from the rear flash); however, that assumption seems to be so obviously correct that no proof appears to be needed, until the same events are examined with the reference frame reversed.
In the reversed reference-frame situation, it is stipulated that the flashes of light occur at each end of a fast-moving train at the moment a central detector on the train is directly opposite a similar detector on the ground. Since the flashes of light will be simultaneous in the reference frame of the train in this case, the Michelson-Morley findings prove that the light from each flash will reach that central detector on the train simultaneously.
But in this reversed situation, it can no longer be argued, as was true in the original experiment, that the light from each flash would have to reach the other detector (the detector on the ground in this case) at different times. On the contrary, if each flash occurs at the moment the linear separation between the ground detector and the central detector on the train is zero (that is, at the moment the ground detector is halfway between the two light sources), there is solid laboratory evidence from binary stars and other moving light sources to prove that the light from each of those flashes would also reach the detector on the ground simultaneously, regardless of any motion of those light sources.
Top of Page Return to #3 Home
Answer to Question #3 in plain EnglishIf large flashbulbs are actually attached at each end of a fast-moving train and if each flash occurs when a central detector on the train is directly opposite a similar detector on the ground (see: Figure C), then light waves will radiate out from each flash in all directions and illuminate everything in sight of those flashes. Those light waves will have to illuminate each of the two detectors eventually.
That much of this discussion is indisputable. The only question is exactly when each flash takes place and exactly when the light from each flash will reach each of the detectors.
Since each flash on the train occurs at a single moment in time (see: FAQ #4 concerning a single moment in time) and the detector on the train is fixed halfway between them, the empirical findings of Michelson-Morley prove that the light from each flash will reach the detector on the train simultaneously.
And since the detector on the ground will be located halfway between the two flashes at the moment they occur, and since the laboratory studies of binary stars and other moving light sources prove that the motion of a light source will have no affect on the speed of light waves leaving that source, there is also solid empirical proof that the light from each flash will also reach the detector on the ground simultaneously.
The finding that each flash will illuminate each detector simultaneously, even though the detectors are continuously moving apart is counterintuitive, but it is not unusual for the behavior of light to prove counterintuitive when closely examined. In reviewing these findings, it is important to set aside intuition and trust the laws of physics. Those laws report empirical findings from the laboratory. Common sense and intuition are not even involved. When carefully applied, the laws of physics are absolutely dependable, which is the important difference between laws and theories in physics.
Top of Page Return to #3 Home
Question #4: The events in these illustrations take place in a moving reference frame, which means the problem of time dilations must be taken into account. Those dilations will affect the appearance of events on the moving train when viewed from the ground. How could these arguments be taken seriously when the problem of time dilations is not even mentioned?Answer to Question #4 It is important not to confuse the concept of 'time dilations' with the concept of a 'moment in time.' They both involve time, but they are different concepts. A 'dilation of time' describes a slowing in the passage of time measured between events in a given reference frame. A 'moment in time' describes when an event itself actually takes place. There is no time interval involved in the latter, so the rate at which time is passing (time dilations) would have no affect and would not enter into that discussion:
For example, if a rocket were passing near the earth while traveling at some relativistic speed, and if the pilot on the rocket had a twin sibling on earth, those twins would be aging at different rates at that time due to the dilation of time onboard the rocket (presumably due to the motion of the rocket with overall respect to all matter affecting it).
If an accident occurred and the rocket crashed into the earth (and into the home of the twin) and both twins were killed, then the twin on the ground would have been older than the twin on the rocket at the moment of death. Time would have been passing at a faster rate for the twin on the ground, so that twin would have lived for a longer interval of time than the twin on the rocket (a longer time as measured by a clock or calendar --something that measures an interval of time). However, both twins would have died at the same moment.
In Figure C, it is stipulated that each flash on the train occurs at the moment the detector on the train is directly opposite the detector on the ground (that is, at the moment the linear separation between the two detectors is zero --when they are at the same location). There are no time intervals involved, so any time dilations taking place in either reference frame would have no affect on this stipulation.
If each flash occurs at the moment the train detector is directly opposite the ground detector (when the lateral separation between them is zero), then it is also true that each flash occurs at the moment the ground detector is directly opposite the train detector. Those are simply different views of the same moment.
Top of Page Overview Home Question #5: Relativity theory is tested every day in laboratories all over the world and no discrepancies have ever been found between the predictions of that theory and the findings in those laboratories. How could a few simple drawings be any concern after decades of proven laboratory results?
Answer to Question #5 It is true that relativity theory correctly predicted much of what was later found to be true in the laboratory, and it is true that that theory has been extensively tested and the tests have upheld that theory with remarkable consistency. But no theory is ever proven correct in a laboratory.
Theories are tested in laboratories, and the tests either uphold the theory or prove the theory wrong. The only way a theory could be proven correct would be to prove that all possible tests of that theory had been run, that all possible questions had been asked, and there would always be at least one test that no one thought to run. One question that no one thought to ask.
In the case of this theory, the tests needed to prove the theory wrong were all carried out long ago ...carried out and replicated and confirmed beyond any reasonable doubt.
Those tests are summarized in Figures A and B, and the outcomes of those tests now constitute the solidly empirical laws of light propagation. The problem has been that certain aspects of those findings have been overlooked. No one thought to examine those earlier laboratory findings in the context (shown in Figure C) needed to recognize that the relativity of simultaneity theory makes certain intuitive assumptions about the behavior of light that are not correct.
In trying to make sense of all this (and this is just speculation, in view of the many successful predictions made by the existing theory and the many laboratory findings that have appeared to uphold that theory), it should be recognized that the most compelling support for relativity theory has come from the behavior of high energy particles traveling at relativistic speeds. And recognize that relativity theory was created to provide an intuitive explanation for the counterintuitive behavior of light found in the early laboratory studies of Faraday and Maxwell and others.
If photons of light can be viewed as high energy particles traveling at relativistic speeds, then it may not be surprising that a theory designed to provide an intuitive explanation for the counterintuitive behavior of those particles (photons) also anticipated the counterintuitive behavior of other particles (protons, etc) accelerated to those same relativistic speeds.
A correct anticipation of how particles such as protons would behave under high energy conditions, based on observations of how other particles (photons) behave under similar conditions, might have nothing to do with the validity of a theory designed to provide an intuitive explanation for what was causing those relativistic behaviors.
In any case, the rules of science are clear in this situation. If a valid test is run on a theory and the theory fails that test, then the theory must be modified to account for that finding, or the theory must be discarded. It would not matter how many earlier tests had upheld the theory. The only conclusion that could be reached in that situation would be to recognize that the earlier tests had not sufficiently tested the theory.
The only way the existing theory could be modified to account for the findings summarized in Figure C would be to prove that the empirical laws of light propagation are wrong (the laws summarized in Figures A and B), and that would be difficult to prove (see: FAQ #1 & #2).
Top of Page Overview Home
P.O. Box 812
Bryans Road, MD 20616
All Rights Reserved
e-mail:rhaubrich@physicsprize.com
