What does it mean for a body to be 'at rest'? I make think I'm stationary while taking a nap, but things are not always as they seem. A recent report in Phys.org suggests that it might be possible to detect whether an observer is stationary or moving by detecting its speed through the Cosmic Background Radiation.
In a new study, scientists have proposed that tiny residual effects measured by ether-drift experiments in the 1920s and '30s may be the first evidence of a temperature gradient that was theorized in the 1970s, but never before detected in a laboratory. The theorized temperature gradient is thought to be caused by the solar system moving at 370 km/sec through the cosmic background radiation (CBR), which is the faint electromagnetic radiation that fills the universe.
The researchers, Maurizio Consoli from INFN [Istituto Nazionale di Fisica Nucleare], along with Alessandro Pluchino and Andrea Rapisarda from INFN and the University of Catania in Italy, have published a paper on their reinterpretation of the ether-drift experiments in a recent issue of EPL [EuroPhysics Letters] .
"The main significance of our work is that those small residual effects found in all ether-drift experiments in gaseous systems, usually considered as uninteresting thermal disturbances, might instead represent the first experimental evidence for the Earth's motion within the CBR," Consoli told Phys.org.
I found this to be interesting:
A difference in the speed of light in any two perpendicular directions in an inertial reference frame would contradict special relativity, since relativity requires a vacuum within which the speed of light is constant. Many important concepts emerge from this fact, including that the universe has no preferred reference frame, that there is no absolute space or time, and that you can never really tell for sure whether you are at rest or in constant motion since all motion is relative.
The researchers found that an analysis of previous interferometer experiments provided an estimate of 370 km/sec of motion with respect to the CBR which is in close agreement to what is predicted by our planet's motion through the solar system and it, in turn, about our galaxy, within our local cluster of galaxies which are heading towards what is called the Great Attractor. (At 370 km/sec, one could take a lap around the Earth at the equator in under two minutes, and travel to the moon in just under 18 minutes!)
ArXiv.org has the full report (pdf) available.
(Score: 3, Insightful) by art guerrilla on Saturday February 20 2016, @04:06PM
so there *is* an aether ! ! !
everything old becomes new again...
(Score: 2) by mhajicek on Saturday February 20 2016, @05:43PM
Now I'm curious about red/blue shift of the CBR.
The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
(Score: 0) by Anonymous Coward on Saturday February 20 2016, @10:56PM
Uh, no, that's not what this is saying.
(Score: 0) by Anonymous Coward on Saturday February 20 2016, @04:32PM
If I understand correctly, special relativity says it is not possible to measure the ether in principle:
https://en.m.wikipedia.org/wiki/One-way_speed_of_light [wikipedia.org]
(Score: 3, Insightful) by AnonymousCowardNoMore on Saturday February 20 2016, @05:08PM
Which is why you're supposed to try. It's how theories are tested. (And more importantly in this case, the experimental result came first. It was only AFTER interferometers failed to find evidence of aether that SR was created as an explanation. Experiments which corroborate the result continue.)
(Score: 0, Disagree) by Anonymous Coward on Saturday February 20 2016, @05:16PM
Its more than testing the theory though. It is that if you accept special relativity then it is impossible for you to measure the aether whether it exists or not. At least using speed of light.
(Score: 2) by HiThere on Saturday February 20 2016, @09:37PM
IIUC, that's not what they're doing. They aren't measuring the speed, but rather the frequency distribution, which IS affected by motion towards or away from the source even under Special Relativity. The *assumption* is that if no motion were present, the frequency distribution would be the same in all directions. But if you move in a direction, you get blue shift in the direction you're moving, and red shift in the direction you're moving away from. Any conclusions about speed require additional assumptions or measurements.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 3, Informative) by maxwell demon on Saturday February 20 2016, @06:16PM
It's a more fundamental problem. Let's take a similar question: An airplane is flying from New York to London. How do you determine how fast it was?
Well, at first it seems a simple problem: You loot at the clock when the plane starts, and look again when it lands, and then you take the difference. However that assumes you can carry a clock with the flight. Now in an airplane that's of course not a problem, but for light it definitely is, as you cannot transport a clock with the speed of light. So to make it more analogous, let's say you are not allowed to take a clock with you.
Well, so what, you say, let's just look at a stationary clock in New York when the airplane starts, and a stationary clock in London when the airplane lands. But wait. The clock in London shows a different time than the clock in New York. If you just subtract the times read from the clocks, you'll certainly not get the flight time.
Ah, you say, but I can correct for that. I just have to correct for the difference between those clocks. But for that you have to determine the difference between those clocks. That is, when you are in London, you have to say what is "now" in New York, and vice versa. In other words, you have to have a protocol to say which time in London corresponds to which time in New York. In other words, you have to synchronize your clocks. Obviously the chosen protocol determines what speed you get from your calculation.
Now the problem is that to synchronize your clocks, you have to communicate. And that means, you have to take the speed of communication into account. But wait, we can't measure that speed before we have synchronized our clocks!
OK, so we've now got a catch-22: To synchronize our clocks, we need to determine the speed of communication. But to determine the speed of communication, we need to synchronize our clocks. So is there a way out?
Well, if we don't take just the flight time from New York to London, but let the airplane immediately turn around and fly back, then we can determine the total time of flight by just looking at the clock in New York. Hooray, no synchronization problems! But now we don't get the one-way speed, but only the average speed of both directions.
OK, but I've got an idea: Let's build a time broadcast in the middle between New York and London. Since it is in the middle, the broadcast time should be the same to New York and to London, so we can use that to synchronize out clocks. Right? But wait: We just assumed that the signal goes with the same speed in both directions. But what if it doesn't? Since we use that very signal to measure one-way speeds, we won't ever be able to detect a difference of the signal speed in both directions, because is simply would drop out of our calculations!
Note that, apart from the fact that you cannot transport clocks with the speed of light, I have made no reference to relativity in these considerations.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by isostatic on Saturday February 20 2016, @07:39PM
You take two identical atomic clocks in new york. You take two in london. You take one of each on a slow boat to the other. You record the time of the 4 clocks.
(Score: 3, Insightful) by maxwell demon on Saturday February 20 2016, @07:56PM
That assumes you can define a "slow boat". That quite obviously depends on your frame of reference.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 5, Informative) by gnuman on Saturday February 20 2016, @05:43PM
special relativity says it is not possible to measure the ether in principle
Special relativity and "aether" theory fundamentally break each other on this principle. Special relativity and general relativity rely on an axiom that there is no preferential reference frame. That everything is relative.
Also, aether was invented to explain how light waves could possibly travel through areas apparently without medium - aether was the medium and was modeled after air or water, like for sound waves. Comic background radiation has nothing to do with aether.
(Score: 1, Informative) by Anonymous Coward on Saturday February 20 2016, @08:18PM
The cosmic background radiation is not uniform in the sky---it's more intense on one side of the sky than on the other. But the intensity difference is easy to explain as a Doppler shift---we're moving through space, so if we look forwards (in the direction of motion) the background light seems a little brighter and if we look backwards (opposite to the direction of motion) it seems a little dimmer. That effect doesn't violate relativity because nobody's saying that the Earth is moving relative to empty space. We're just moving relative to the background radiation. You're at rest with respect to the background radiation if it has the same intensity in every direction.
The background radiation is mostly radio waves, which can pass through walls. (This is why your cell phone works indoors.) So in a perverse sense, a little tube of gas sitting on a laboratory table will be able to "detect" that more radio waves are coming from one side of the sky than from the other. And back in the 1920s and '30s, the interferometers used to detect aether drift involved shining light back and forth in a little tube of air. Nobody builds interferometers like that anymore because they air is sensitive to small thermal gradients---if one side of the tube sees a higher temperature than the other it hurts your results. But in the 1920s it was a lot harder to get a good vacuum, so they made do with what they had.
The paper in question notes that some of the aether drift experiments from the 1930s did detect small directional effects, but the effects weren't always reproducible and they were much smaller than the non-relativistic aether theories expected, so they were written off as thermal effects. The authors of this paper suggest that the thermal effects in question are actually thermal effects resulting from the cosmic background radiation, and that nobody realized this before because nobody cared---all the good modern interferometers use vacuums to eliminate the effect. The authors notice that when the effect was detected (note that it wasn't always reproducible) it seemed to have the magnitude you would expect if it were caused by the background radiation. So they're asking someone to use the latest-and-greatest inteferometer technology but with an air-filled tube instead of a vacuum, and see if the effect can be observed again today.
(Score: 2) by maxwell demon on Sunday February 21 2016, @01:12PM
If it's the background radiation, the effect should go away also if you put the whole interferometer in a Faraday cage, as that would block the background radiation.
The Tao of math: The numbers you can count are not the real numbers.