GPS with relativistic nanosecond time differences? Luxury! When I were a lad we 'ad to make do with Decca!
(Actually, I really liked Decca)
The European Space Agency is to make the most of two satellite misfires by using them to test Einstein's theory of relativity. Last August, the fifth and sixth Galileo satellites were launched as part of a plan to create a Euro-run GPS system, but the launch didn't go according to plan. A failure in the fourth stage of the …
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What the linked article actually says is:
"Albert Einstein predicted a century ago that time would pass more slowly close to a massive object. It has been verified experimentally, most significantly in 1976 when a hydrogen maser atomic clock on Gravity Probe A was launched 10 000 km into space, confirming the prediction to within 140 parts in a million."
Which I'm sure we can all agree makes a lot more sense than the plain wrong version in the report.
Thanks YAAC! I'd not heard of that before, (the Pound-Rebka experiment for those interested).
Forget the bad English; anyone else notice that it makes no sense numerically?
"140 parts in a million" is about 12 seconds PER DAY.
You could measure that with a grandfather clock for gawd's sake (perhaps not in zero g).
It's OBVIOUSLY INCORRECT as written.
You could measure that with a grandfather clock for gawd's sake (perhaps not in zero g).
Just attach a suitable spring to the pendulum bob, with the other end anchored to the floor of the cabinet. I think that's the only gravity-sensitive part of the typical grandfather clock.
Hmm, now I'm wondering if that would work. The downward force due to gravity on the pendulum of a grandfather clock is constant to a first approximation, since its distance from the Earth's center of mass doesn't change significantly. But its distance from the proposed spring's attachment point does, and by Hooke's Law that means the force on the bob is going to change proportionally. I don't know much about the actual workings of grandfather clocks (I mean, I know the general theory, but not the practical details), but I suspect the spring would rather dampen the action.
Maybe two springs, each attached to one corner of the cabinet? Or two springs running vertically along the sides of the cabinet and connected to a cable that runs through a pulley that replaces the bob.
I'd google "grandfather clock in space", but I'm afraid I'd find something relevant.
I'm hoping for a "Hmmm, that's odd." discovery in the data.
The biggest breakthroughs have started with those words.
Gravity is the one force we really don't understand very well, hence the need for dark mater/energy to explain why really big things don't behave how the math says they should.
And that's how science works.
Religion: Our book is universal truth because we'll kill anyone who says that it isn't.
Science: Our latest theory seems to be pretty good, so we'll test it to within an inch of its life to try and find holes in it. If it passes that's very good, because it's more reliable. If it fails that's marvellous, because we've found new knowledge about how the Universe works.
"And that's how science works."
Are you sure?
Science that can be easily verified: We'd better test this theory to an inch of its life because we'll look like fools if we're wrong.
Science that can't be easily verified: We'll test this theory a bit, and if the results look dodgy, we'll adjust the data, tweak the models, and call anyone who doubts us a denier. After all, we know we're right.
Sure - scientists are human. And they are subject to all sorts of pressures. Especially the 'publish or perish' idiocy.
But they do the best they can. And they punish cheating wherever they can.
Science is a long way from perfect - but it is leaps and bounds better than anything else. And at the end of the day, you can't fool the Universe.
We are having this discussion on a system that was made possible by an enormous number of scientific and technical advances, each itself made possible by previous advances. Many of us are only alive due to medical advances.
...and a great many more are not alive anymore either a) because the relevant medical advances were either somehow not made at all (and don't seem to be forthcoming in the foreseeable future either in spite of many decades of "study"), b) because they could not afford to pay for it or c) because ultimately you're just disposable meat to any doctor and none of them will lose a second of sleep whether you live or die. </rant> Sorry, pet peeve triggered... the rest of your argument is quite valid.
"And that's how science works."
"Are you sure?"
Yes. You are confusing science and scientists. The latter are squishy meatbags susceptible to the full range of human foibles - mistakes, fraud, political pressure, egos, and so on. The former is not. It doesn't matter how much you screw up or fake your results now, when someone repeats the same experiments (or different ones looking at the same thing) next month, next year, or next century, they will find out and correct things. Anti-science nuts love to posit grand conspiracies covering the whole world and running for centuries, but in the real world science is inevitably self-correcting in the long term.
No, the science works all by itself, without any need of assistance from anyone (except mother nature).
You just need the scientists to try and understand the why and the how, if you so desire to do so.
The sun is going to come up, set and generally move about in the sky no matter whether you believe celestial mechanics, God and/or a huge Egyptian scarab beetle are causing it.
"No, the science works all by itself, without any need of assistance from anyone (except mother nature)."
Perhaps this is a semantic matter, but by all definitions I'm aware of, science is very much in the human realm. We can crudely define it as "our understanding of the natural world". Nature works all by itself; science is encumbered by us fleshy things with our microscopes, rulers, hormones, and correlation formulae.
Sorry to nark on. My original post was meant to be jocular. I absolutely agree with Christoph's description of science, but I also believe it is an idealized notion. Robert Grant above used the phrase "science mission statement", and I understand his concerns about how it is proselytised. My own view is that what separates (should separate?) science from religion and other non-rational beliefs is ignorance. The religious believe they know everything; scientists are certain they know very little. But finding out just a little bit more is the motivation.
No, the science works all by itself, without any need of assistance from anyone (except mother nature).
And you are confusing science and the physical universe it describes.
Even (non-naive) realists don't believe science is the physical universe - they just think it can (ideally) be an accurate description of things that are true ("facts") about the physical universe, and a set of protocols for discovering those facts. ("Discovering" in this sense implies some degree of realism.)
Conversely, very few constructivists or other anti-realists believe there is no indexical relationship whatsoever between scientific epistemology and material existence, even if they posit the latter as not directly knowable. But that's another question.
Just never forget that 'science is self-correcting', ...
Which directly implies that some peer-reviewed, journal -published, generally-accepted scientific facts are actually 'yet to be corrected', in other words WRONG.
(No, this is not a climate 'denier' rant.)
My target is more often the ever-changing HEALTH / DIETARY crap "science" which is literally more often wrong than right. Moderation and common sense is literally more accurate in the long run. They've done nearly as much harm as good with their rubbish science.
The Economist 'Trouble at the Lab' article provides background info.
albaleo wrote:
Science that can't be easily verified: We'll test this theory a bit, and if the results look dodgy, we'll adjust the data, tweak the models, and call anyone who doubts us a denier. After all, we know we're right.
That's why climate change is a religion, not a science.
"Who demands we all accept that "The science is settled!"?
The Warmists or the Skeptics?"
ROFL!
The science is settled because the data and evidence overwhelmingly shows that anthropogenic climate change is actually happening, to a very dangerous extent, and is getting rapidly worse.
Are you seriously saying that this should be doubted because the evidence is so good?
That you would only take it seriously if there was less evidence?
That the 'Skeptics' are correct because they can't substantiate their case with actual evidence?
I would bet some money they were not insured. NASA does not insure its launches and I would expect ESA to follow this practice. The reason is in the long run you must be paying more for insuring than not insuring. The difference is the insurer's premium.
It is very similar to why car rental companies are "self insured" (that is they are mot insured at all). I the long run they have to lose money insuring their cars - and they operate in the long sun (as do the space agencies). You need insurance only if the costs of a single mishap can be too much for you to handle and for state run agencies on yearly budget a single failure in not a financial catastrophe.
@ Little Mouse
You can of course tweak the average speeds on various types of road that it uses to calculate the journey time. I find Copilot times pretty good when setup, compared to default values which see you arriving 10-15% earlier than calculated. (Sat nav capabilities vary and are available from other vendors).
For once I haven't been to the cited article to check things, but I think this is more about the science than any improvements to GPS.
There is a lot of interest in test General Relativity to its limits. Over the years "boffins" (in Reg speak) have produced lots of little refinements to GR that predict pretty much the same results as Albert, but with subtle (hard to measure) differences. Which, if any, of these more sophisticated models is right is interesting science wise. I doubt that the real world impact will be that great because wobbles in satellite orbits and other factors will mask these very minor corrections-if they didn't then we'd be able to measure them already using the GPS system.
My suspicion is that the variation caused by the distortion would be much too small to register on this experiment. Given that the difference in time between two altitudes for the entire mass of the Earth is 140 parts per million I think any distortion will add the tiniest of variations to that.
But, I could be wrong.
JM "Given that the difference in time between two altitudes for the entire mass of the Earth is 140 parts per million I think any distortion will add the tiniest of variations to that."
Check your math.
140 ppm is about 12s per day of your purported "difference in time between two altitudes".
We would have noticed that, even with a grandfather clock.
The article was written incorrectly.
"The Sun and Moon may distort the shape of the Earth, but Shirley it's the mass that matters?"
The distortion will mean that some of that mass will be closer to, or further from, the satellites than on average and therefore there will be variation in the gravitational field and variation in the relativistic effects.
My old physics teacher would turn in his grave after spending a lifetime forcing us that it's only the centre of gravity that counts. But that's theoretical physics for you.
That said, even that must shift around a bit in a three-body system. Then factor in all the other bodies moving around out there. And the fact that the masses of the Sun, Earth and Moon are always changing.
So I concede that there will always be some distortion.
"In theory, there is no difference between theory and practice. But in practice, there is."