Einstein's Theory of Relativity, Critical For GPS, Seen In Distant Stars (phys.org) 48
Using NASA's Chandra X-ray Observatory, astronomers have discovered that "gravitational redshift" exists in two stars orbiting each other in our galaxy about 29,000 light years (200,000 trillion miles) away from Earth. Gravitational redshifts, where light is shifted to redder colors because of gravity, "have tangible impacts on modern life, as scientists and engineers must take them into account to enable accurate positions for GPS," reports Phys.Org. From the report: The intriguing system known as 4U 1916-053 contains two stars in a remarkably close orbit. One is the core of a star that has had its outer layers stripped away, leaving a star that is much denser than the Sun. The other is a neutron star, an even denser object created when a massive star collapses in a supernova explosion. The neutron star (grey) is shown in this artist's impression at the center of a disk of hot gas pulled away from its companion (white star on left). These two compact stars are only about 215,000 miles apart, roughly the distance between the Earth and the Moon. While the Moon orbits our planet once a month, the dense companion star in 4U 1916-053 whips around the neutron star and completes a full orbit in only 50 minutes.
In the new work on 4U 1916-053, the team analyzed X-ray spectra -- that is, the amounts of X-rays at different wavelengths -- from Chandra. They found the characteristic signature of the absorption of X-ray light by iron and silicon in the spectra. In three separate observations with Chandra, the data show a sharp drop in the detected amount of X-rays close to the wavelengths where the iron or silicon atoms are expected to absorb the X-rays. One of the spectra showing absorption by iron -- the dips on the left and right -- is included in the main graphic. An additional graphic shows a spectrum with absorption by silicon. In both spectra the data are shown in grey and a computer model in red.
However, the wavelengths of these characteristic signatures of iron and silicon were shifted to longer, or redder wavelengths compared to the laboratory values found here on Earth (shown with the blue, vertical line for each absorption signature). The researchers found that the shift of the absorption features was the same in each of the three Chandra observations, and that it was too large to be explained by motion away from us. Instead they concluded it was caused by gravitational redshift. The article goes on to explain how gravitational redshifts connect with Einstein's General Theory Relativity: "As predicted by Einstein's theory, clocks under the force of gravity run at a slower rate than clocks viewed from a distant region experiencing weaker gravity. This means that clocks on Earth observed from orbiting satellites run at a slower rate. To have the high precision needed for GPS, this effect needs to be taken into account or there will be small differences in time that would add up quickly, calculating inaccurate positions..."
The findings have been published in the Astrophysical Journal.
In the new work on 4U 1916-053, the team analyzed X-ray spectra -- that is, the amounts of X-rays at different wavelengths -- from Chandra. They found the characteristic signature of the absorption of X-ray light by iron and silicon in the spectra. In three separate observations with Chandra, the data show a sharp drop in the detected amount of X-rays close to the wavelengths where the iron or silicon atoms are expected to absorb the X-rays. One of the spectra showing absorption by iron -- the dips on the left and right -- is included in the main graphic. An additional graphic shows a spectrum with absorption by silicon. In both spectra the data are shown in grey and a computer model in red.
However, the wavelengths of these characteristic signatures of iron and silicon were shifted to longer, or redder wavelengths compared to the laboratory values found here on Earth (shown with the blue, vertical line for each absorption signature). The researchers found that the shift of the absorption features was the same in each of the three Chandra observations, and that it was too large to be explained by motion away from us. Instead they concluded it was caused by gravitational redshift. The article goes on to explain how gravitational redshifts connect with Einstein's General Theory Relativity: "As predicted by Einstein's theory, clocks under the force of gravity run at a slower rate than clocks viewed from a distant region experiencing weaker gravity. This means that clocks on Earth observed from orbiting satellites run at a slower rate. To have the high precision needed for GPS, this effect needs to be taken into account or there will be small differences in time that would add up quickly, calculating inaccurate positions..."
The findings have been published in the Astrophysical Journal.
Ye old dog Einstein (Score:2, Offtopic)
That confounded theory of relativity .. pisses me off how true it is. The speed of light is too fucking slow for me.
Re: (Score:2)
Re:Ye old dog EinSWASTIKA!!! (Score:4, Interesting)
Why do you keep posting an ancient symbol for good fortune? Are you trying to wish us all good luck?
https://en.wikipedia.org/wiki/... [wikipedia.org]
Re: (Score:1)
Re: (Score:2)
"I am from Spain and there isn't exactly a big jewish community over here. "
Small wonder, the Alhambra Decree gave all Jews the choice between converting to Catholicism, exile or death in 1492.
But still, nowadays there are 63000 there.
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
"Critical for GPS" ?! WTAF ? (Score:5, Insightful)
Seriously ? You edit a News For Nerds site and you think that belongs in the headline ? Pathetic
Re: (Score:2)
Re: (Score:1)
Re: (Score:2)
Erm, that's the point.
I thought my comment was clear, but I will elucidate:
Saying a theory is "critical for GPS" is the sort of dumbing down a lazy journalist does to try an make a story more relevant to the general public.
But Slashdot is News for NERDS.
We are people who know that basic physical theories are critical for EVERYTHING, without being given lame tags like "critical for GPS".
But either the Slashdot "editors" do not know that, or they assume Slashdot readers do not.
I don't know which is worse.
Re: (Score:2)
clearly, it's for the Galactic Positioning System.
You could end up missing your destination by three or four solar systems without it!
hawk
Intriguing (Score:2)
It was hard to believe (Score:4, Informative)
I remember reading an item in Scientific American (the history item I think) about when the first GPS satellites were being launched in the '60s that they had a software-settable option to control its relativity adjustment function. Set one way there would be no relativistic correction and set the other way it would.
What that says is that there were scientists/engineers in the project, highly placed and supposedly highly credentialed, that did not accept that the theory of relativity was "real." I am not clear on the history but I thought that at time relativity was already supported by observations.
BTW I was surprised to learn that if you do not correct for relativity in GPS with geosynchronous satellites, the error accumulates at something like 11 miles a day. Pretty amazing when you think of it.
But also amazing when you realize that top scientists would reject their education in favor of "common sense."
Re: (Score:2)
I am not sure what experiment you are referring to. I am interesting about reading the article or the experiment description and results. I find it hard to imagine that scientists would doubt relativity. Engineers, perhaps, but not scientists.
What I can find is that in 1971, there were tests using cesium clocks on airplanes flying around the world, the Hafele-Keating experiment [gsu.edu], and it did agree with the special and general relativity effects.
Re: (Score:2)
I should have known there was a Wikipedia article for it. Tests of general relativity. [wikipedia.org]
The evidence goes back to the early part of the century but I didn't know there were so many of them.
Re: (Score:1)
Well, on the other hand, this may be taken as an experimental test of the theory. Scientists are not supposed to have blind faith, it's in the job requirements. Even though it may be a well established theory, it must be tested.
Re: (Score:2)
BTW I was surprised to learn that if you do not correct for relativity in GPS with geosynchronous satellites, the error accumulates at something like 11 miles a day. Pretty amazing when you think of it.
This is a myth. You don't have to correct for anything to make GPS work. So long as the constellation has synchronized clocks you can accurately determine position. The clocks will certainly drift... but receivers get their clocking from GPS so it makes no difference there is certainly an accumulation of error in time but not position.
Re: (Score:2)
From the wikipedia article [wikipedia.org] on this:
When combining the time dilation and gravitational frequency shift, the discrepancy is about 38 microseconds per day, a difference of 4.465 parts in 10**10.[16] Without correction, errors of roughly 11.4 km/day would accumulate in the position.[17]
So 11 km not 11 miles. My bad.
Re: (Score:2)
BTW I was surprised to learn that if you do not correct for relativity in GPS with geosynchronous satellites,
Also GPS satellites are not geosynchronous not even close.
Re: (Score:1)
Re: (Score:1)
GPS satellites transmit data at 10.229 999 995 43 MHz based on their atomic clocks and is received at 10.230 000 000 00 MHz. The error is predicted by GR. If you don't correct for this the time from the satellites' clocks slowly start to disagree with the clock in the receiver (the satellites' clocks will be running too fast). The GPS locations calculated will gain an error of about 10km every day.
Your "analysis" is in no way a proof against SR or GR.
Re: (Score:2)
GPS satellites transmit data at 10.229 999 995 43 MHz based on their atomic clocks and is received at 10.230 000 000 00 MHz. The error is predicted by GR. If you don't correct for this the time from the satellites' clocks slowly start to disagree with the clock in the receiver (the satellites' clocks will be running too fast). The GPS locations calculated will gain an error of about 10km every day.
Parent is correct. It is quite possible to design an accurate GPS system with total ignorance of relativity.
Keep in mind receivers any of us can afford get their clocking from GPS itself rendering 10km a day an irrelevant metric. Whatever contributions of ignoring relativity in mechanics of satellite determining its own position is way less than error contributions of ionospheric delay.
Re: (Score:2)
Sure. You could. But you'd have to make corrections for Relativistic effects.
Why?
Also, the satellites do not determine their own position.
The satellite determines its position based on data uploaded to it by ground stations.
Re: (Score:2)
At a minimum the receiver must assume the speed of light is constant.
You are just throwing shit on the wall and none of it is sticking.
GPS also assumes some other things for which Relativistic corrections are required.
What things?
Red shift due to enormous acceleration? (Score:2)
Armchair astrophysicist here.
My informal understanding of General Relativity is that there is some kind of equivalence between gravitational force and inertial force due to acceleration. What I get from the article is that this binary system is remarkable for the close proximity and rapid orbital speed of two stellar mass objects. I do not think either of the objects is particularly massive, not compared to a supermassive black hole at the center of a galaxy. So I suppose you could call the spectral line sh
Still a theory? (Score:2)
It is about time to promote Einstein's "theory" to "law" status. Relativity is every bit a proven as Newton's laws of motion. Yes, it's still as strange as it ever was. Turns out the universe is strange when you look closely.
How do you see a theory in a distant star? (Score:1)
Did somebody send a pamphlet of Einstein's theory to Betelgeuse or something?