Slashdot Mirror
General Relativity Is At Least 99.95% Right
ultracool writes to mention a ScienceDaily piece on compelling proof of general relativity. A team at the University of Manchester have used three years' worth of data on a pair of pulsars as a litmus test, against which they've benchmarked Einstein's theory. From the article: "Though all the independent tests available in the double pulsar system agree with Einstein's theory, the one that gives the most precise result is the time delay, known as the Shapiro Delay, which the signals suffer as they pass through the curved space-time surrounding the two neutron stars. It is close to 90 millionths of a second and the ratio of the observed and predicted values is 1.0001 +/- 0.0005 - a precision of 0.05%. A number of other relativistic effects predicted by Einstein can also be observed. 'We see that, due to its mass, the fabric of space-time around a pulsar is curved. We also see that the pulsar clock runs slower when it is deeper in the gravitational field of its massive companion, an effect known as "time dilation."'"
Observations that support a theory are nice, but they are not a proof.
I think what they mean to say is that "Reality is at least 99.95% right."
Let's not go attempting to invalidate any theories I've spent hundreds of hours trying to understand, ok?
When things get complex, multiply by the complex conjugate.
all we need are 20 pounds of trash and 1.2 jigawatts from the town square clock at midnight!
I think 99.95% is about as close to dead-on-balls-accurate as it gets with our current knowledge of the universe; I mean, there's always a margin for error in absolutely everything, it's just one of the facts of the chaotic universe in which we live. Still, it just goes to show how far ahead of the game (and of the times) Einstein was.
Einstein's still my hero. He's the Samuel L. Jackson of science.
[End of Line]
"Well, I measured thousands of falling apples, my mechanics must be at least 99.95% right!"
However, General Relativity is not a proof, but a model. The various models that give us a way of understannding the world are only that: models, not laws per se.
When Newton explained gravity, he did not say that he was right. Indeed he said that the model he proposed was the best he could come up with given the limitations of his apparatus. He even predicted that his model would be superceded. And, for most people of today, the physical objects that they interact with can be adequately understood with Newtonian physics.
Einstein even said "As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality.". Just like Newton's models had limits and fell apart at some point, likely the same will happen to General Relativity when we're one day able to observe things beyond what the model can handle.
Engineering is the art of compromise.
(sorry)
"" How about taking the safety labels off everything, and let the stupidity-problem solve itself? """
What the fuck?
Maybe I don't know about the "Cartesian method of doubt", but it doesn't have anything to do with physics. Are you saying that if I measure something with a ruler, I should throw in a couple extra percentage points to the error calculation because I'm not sure if the universe exists? Jesus. Even if I *should*, what percentage should I throw in?
I'm aware that my post was not directly responsive to your point, but I could smell it provoking an attack of the "It's only a theory" people and I wanted do what I could to head them off at the pass.
KFG
What they mean by "99.95% right" is not that there is a 99.95% probability that Einstein's theory is dead right, and correct, and a 0.05% probability that it is dead wrong. It simply means that to the extent of their capabilities, they have determined that Einstein's theory is accurate in predicting other observations to 99.95%. It might be wrong at the 150th decimal place. But then again, they don't really have the ability to verify that. So for now, they've verified it's accurate in predicting other observations to at least 99.95%. Maybe next year (with a 4th year of measurements, or with better equipment), they can say it's accurate to 99.995%.
Cheers, Too Lazy to Create and Account Andreas.
How can they say anything is 99.95% right, have they never heard of the Cartesian method of doubt. . .
.05%. They are perfectly aware of the lack of knowledge that could be hiding in that .05%, but that .05% defines the limit of our lack of knowledge.
.so all in all I'd say about 1-5% doubt - but you can never know
Yes, that's why they said what they said, i.e. that they have only shown the predictive accuracy of Relativity to a margin of error of
. .
And this makes no sense whatsover, because you are just pulling numbers out of your ass. Yes, it's true that you can never "know," but you can measure and increase the degree of your surity.
KFG
Go back to the philosophy department. No, don't reply; just go.
This is Physics, not Epistemology, dipshit.
Oh wait, you're a troll.
Nice one, centurion. Liked it, liked it.
$30 Off All Plans: Use code TRIPLESAWBUCK
That's not quite true, there could be a non-linear effect. "99.95% right" is a very stupid way to represent this result, but it is slashdot... for mainstream nerds. :P
(Oh, and IAAP)
in this shop we shoot for five nines!
Yes, it's true that you can never "know," but you can measure and increase the degree of your surity.
Amen!
Much the same way your post is 98% correctly spelled, and since we can measure that we can also increase the degree of spelling surety. =)
I figure if Shapiro can get O.J. Simpson off, he has to know something...
788652 = 2 x 2 x 3 x 3 x 19 x 1153
Much the same way your post is 98% correctly spelled. . .
.since we can measure that we can also increase the degree of spelling surety. =)
I think that's better than my average.
. .
Only within the limits of my nuerologcial capabilities, which are below average; and within the limits of my understanding of spelling, which is, in fact, well above average. I deny your authority, but accept both Webster and Chaucer as among the available references.
KFG
Ok, so Relativity and Quantum Mechanics have been beating the crap out of each other for 80 years, with no end in sight. We get it, we get it!
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
. . .there could be a non-linear effect. "99.95% right" is a very stupid way to represent this result. . .
How long is your ten foot pole?
KFG
You can't measure position in quantum physics [...] As far as we known, the "particle" *NEVER* has an exact position or momentum, but rather is at an infinite set of locations.
At least in principle, you can measure position in quantum physics. The particle is temporarily put in a position eigenstate with an exact position eigenvalue associated with it (the momentum is completely indeterminate, however). This only lasts for an instant, however, before the state evolves into a superposition of position eigenstates.
Remember, it is an axiom of quantum mechanics that measuring observables puts the system in an eigenstate of that observable; the eigenvalue corresponds to an exact measurement of that observable. (You will not be in an eigenstate of any observable that commutes with it, and therefore those quantities will not be known exactly — the Heisenberg uncertainty principle.) Of course, you could quibble about our practical ability to put a particle into an exact position eigenstate, as opposed to an eigenstate of an observable merely very similar to the position operator.
Perfectly cromulent word.
Bot Assisted Blogging
Perfectly cromulent word. :)
.English.
Vowel shifts do not create cromulence. Empirical observation suggests they create . .
KFG
And vowel removal? What then? Welsh?
I drank what? -- Socrates
there is no such thing as "fabric of space-time". It's a convenient buzzword but it doesn't mean anything
Of course it means something: it is a summary of the distance and time measurements we make, and can be described in terms of geometrical curvature. If it didn't mean anything, then it wouldn't have any observable consequences.
Things work as if Einstein was right, but there is no evidence that he was right.
You're splitting hairs that don't exist. "Working as if Einstein was right" is "evidence that he was right". It's the only kind of evidence possible.
If you pass a current through a wire it generates a magnetic field. If that field crosses another wire it generates a current in that wire.
That's not necessarily true. A static magnetic field doesn't induce a current in a wire. You might be talking about alternating current, which produces a time-varying magnetic field.
It's exactly as if the magnetic field moved from one wire across the other.
I don't know what you mean by a magnetic field "moving", but certainly the magnetic field of one wire can intersect the position of another wire.
The flaw is that if you wrap both wires through an iron donut all the field is inside the iron - absolutely NO field is detected anywhere around either wire.
Perhaps I'm visualizing the geometry wrong, but your statement appears to be false.
The theory is false, but it is "exactly as if" it were true.
What theory? That the (time-varying) magnetic field produced by one current can induce a current in another wire? That theory is always true. (Of course, you have to take into account induction from other objects which may cancel that current.)
Likewise, Einstein's theory may give correct answers even though nobody actually knows why.
It is not possible to know "why" a theory is true, at least if that theory regards some fundamental phenomenon. It's possible to explain "why" some approximate theory is true by deriving it from a more fundamental one, assuming the more fundamental theory is true.
For one thing, plasma physicists can easily explain a lot of effects in electrical terms, relying on laboratory observations instead of imagined theories.
Nonsense. Plasma physicists use theories just like any other physicist does. Those theories of course are electromagnetic in nature.
Astronomers ignore plasma physics because nobody ever taught it to them.
More nonsense. Plenty of astronomers use plasma physics. What are you, an Alfven plasma cosmology crackpot?
Isn't that (at most) 0.05% the most interesting part?
The more evidence we have to support the fundamentals of the General Relativity model, the more reason we have to suppose that it's more exotic predictions, such as worm holes, are correct.
Assuming we haven't nuked or gassed ourselves into oblivion, I like to imagine in a few hundred years we'll come to regard the work of Einstein, Hawking, Heisenberg, etc. as certainly great but somewhat primitive and rudimentary in our understanding of the universe.
After all, when Archimedes famously realized the principals of buoyancy around 250 BC, it was one of the revelations of its time.
Obviously, you never had any education about electrodynamics, or you would recognise your example as bullshit.
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
* ... Ratios have two numbers ... *
...*
*... the ratio of the observed and predicted values
what are they missing?
I thought that the Boomerang Project from 1998 and 2003 proved that beacuse the background radiation in space was spread out the way it is, that this disproved that Space-Time was curved? Check out http://cmb.phys.cwru.edu/boomerang/. Not that I wanted this to be true, but what I watched on NASA TV in 2003 said that it was the facts. So if his General Theory is 99.95% accurate, is this the .05% variance?
"I think you know what I'm talkin' about, Mr. President; We're gonna kill us a mummy!" - Bruce Campbell as Elvis Presley
well depending on what the ruler's speed relative to your speed is, it may very well appear to be a bit longer than it actually is. If the ruler were falling into a black hole while you watched from a safe distance, it would look VERY long. So the answer to your question is, possibly yes.
But here on earth both you and the ruler are travelling at the same speed and therefore you don't need to do any length compensation calculations.
"Fabric of space-time" was basically a reference to how the theory was demonstrated: lighter and heavier balls on a stretched piece of fabric, which would demonstrate to non-scientists what he meant about time "warping" around large mass objects...
I guess just about every author of algebra, geometry and trig textbooks in the days before trig calculators was "sloppy", because every one I remember seeing titled titled the tables as something like "Table of Trigonomic Ratios", even though the tables were columns of numbers (the quotients).
... mind translating your .sig?
Ignore this signature. By order.
Hello:
The measurement is still in the range of first order parametrized post-Newtonian accuracy. What the Donkey Kong that means is that these are the coefficients to the metric that are being tested:
dtaU^2 = (1 - 2 GM/c^2 R + 2 (GM/c^2 R)^2) dt^2
- (1 + 2 GM/c^2 R) dR^2/c^2
- R^2/c^2 dtheta^2
- R^2/c^2 sin^2 theta dphi^2
It is the 5 integers there (1, -2, +2, -1, -2) that are confirmed by this experiment. That is NOT NEWS, because it is not new. Shapiro got the same results. What would be news is if the experiment got to second order parameterized post Newtonian accuracy. I asked Prof. Clifford Will an expert on experimental tests of GR when where the data hunters going to gather that data. He said he knew of no one even discussing it. The reason is that the data must for 2nd order PPN effects must be a million fold more accurate, so we need data that is 99.99995% accurate.
I care a lot about 2nd order PPN tests, since that is were my proposal to unify gravity and EM using a 4D wave equation differs. GR says the metric should go here:
GR:
dtaU^2 = (1 - 2 GM/c^2 R + 2 (GM/c^2 R)^2 -3/2 (GM/c^2 R)^3) dt^2
- (1 + 2 GM/c^2 R + 3/2 (GM/c^2 R)^2) dR^2/c^2
- R^2/c^2 dtheta^2
- R^2/c^2 sin^2 theta dphi^2
GEM (gravity and EM):
dtaU^2 = (1 - 2 GM/c^2 R + 2 (GM/c^2 R)^2 -4/3 (GM/c^2 R)^3) dt^2
- (1 + 2 GM/c^2 R + 2 (GM/c^2 R)^2) dR^2/c^2
- R^2/c^2 dtheta^2
- R^2/c^2 sin^2 theta dphi^2
At first order PPN accuracy, the coefficients (1, -2, 2, -1, -2) are the same. At second order, they are different. That's the data I need. I'll probably be dead before it shows up.
doug
Working on new views of old physics at http://VisualPhysics.org
Isn't Einstein's relativity just a much smaller magnitude extra term on Newton's mechanics? Negligible at human scales. Einstein's correction to Newton was much less than 0.05%. If relativity is really as much as 0.05% off, that leaves a vast amount of unexplained phenomena in our big Universe.
--
make install -not war
"...there is no such thing as "fabric of space-time""...
It's just a way at looking at the WSOGMM (Whole Sort of General Mish-Mash). A way of defining things from our perspective. It may have been a joke, but I think that Adams was on to something.
huh?
Which is the observed and the predicted value? They only give one number, 1.0001.
There is no known rational explanation for Welsh.
KFG
I do hope they're not actually teaching this in science classes! Darn Evilutionists must be everywhere. Where's my theory of Creative Gravity, eh?
Ok, let's try this: "the earth just sucks!"
I'm quite sure you'll find both values in the original scientific publication.
The Tao of math: The numbers you can count are not the real numbers.
"Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know."
--Donald Rumsfeld
Hear recorded Slashdot headlines on your phone! New service beta testing. Just call (248) 434-5508
As a result, the best we can say is that the theory we have put together fits the observed data to a high degree of precision - but that this may be invalidated at any time by new phenomena. See, for example, the progression from Newtonian mechanics to Relativity, or the long-running debate over the nature of light.
Well, no, that's not the "best" we can do. It is quite possible to prove theories to be correct experimentally, if you formulate the theories correctly and then conduct the right kinds of experiments.
The problem is that General Relativity, like most physical theories, was pulled out of a hat and has caught on because it's appealing to physicists. Furthermore, the experiments being conducted to test those theories are chosen rather haphazardly. For those kinds of theories and those kinds of experiments, it is indeed impossible to prove anything
Uhhh, I thought it was a reference to the concept that you're moving through the 4-dimensional space/time continuum at the speed of light, always at the speed of light, and hence when you move pitifully slowly in the spacial dimensions, you must therefore slow down somewhat in the time dimension.
And I can personally confirm that heavy balls stretch pieces of fabric.
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
> If the ruler were falling into a black hole while you watched from a safe
> distance, it would look VERY long. So the answer to your question is, possibly yes
Yes, but anything that was next to it would be stretched identically, and hence the gradients would still read true, even if it looked odd to the distant observer.
Except for Superman, The Hulk, The Juggernaut, and The Silver Surfer, who can hold black holes in their hand.
It occurs to me the comic book writers might not have fully considered the ramifications of Einstein's theories when writing those stories.
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
> That's not quite true, there could be a non-linear effect. "99.95% right" is a :P
> very stupid way to represent this result, but it is slashdot... for mainstream nerds.
Or, as we computer "scientists" might say, there could be a "horizon effect" (nothing to do with black holes) wherein severe differences don't show up until you measure closely enough. This includes your non-linear effects, and others as well, like the precession of Mercury's orbit, which is as far from a non-linear "tail end" effect as you can get.
RIANARSIHABBBBBBB--IS -- Remember, I am not a real scientist. I have a Bbbbbbbbachelor's degree -- in computer science!".
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
> How long is your ten foot pole?
Umm, it depends if it's "packed for storage" or not. What what? Oh, what now!
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
There's no such thing as proof of a scientific theory, so talking about how a theory is "almost proven" is just plain wrong.
And trying to quantify the "provenness" of a theory with a figure also shows a deep misunderstanding of how science works. There are any number of quantifiable tests that have matched general relativity's predictions, and each of these have different error bars. So picking one at random and using it as the measure of how "proven" general relativity is doesn't make any sense at all.
Since when is 99.95% a big number when we're dealing with astronomy? I think Newton's laws are precise within 99.95%.
99.95% of what?
http://outcampaign.org/
99.95% correct still leaves tremendous room for unknowns. It's that last 0.05% where all the interest lies - where we fail to predict accurately because we are wrong about whatever is occuring.
..........FULL STOP.
To me this just seems like a play on words. Observation is the only way in which we can test the validity of a model. If the model fits experimental data consistently and throughout a large number of experiments, we can only conclude it is right -- at least until someone makes an experiment whose results disprove it, but that's part of the nature of a scientific theory.
I don't understand the last sentence, perhaps you could put it in other words.
I believe you're wrong, unless I haven't understood what you're trying to do with the iron and the wires.
Score: i, Imaginary
Wow, when did you go to school? I learned sqrt(-1) = i in the 10th grade... However, point taken.
The part about "physics and other sciences" is dead on. The only true reality is the position and momentum of the base particles. Everything else are just stories, accurate to some degree - or as you state, "partial data".
However, your statements about math are off insomuch as you use the word "all": one of the most fundamental parts of math and logic were Godel's Incompleteness theorems in the 30s. This is the mathematical codification that Hericlitus ("We both step and do not step in the same rivers. We are and are not." - Wkpda) and the Buddha had it right, (to the Buddha, the Absolute Truth was that "there is nothing absolute in the world, that everything is relative, conditioned and impermanent, and that there is no unchanging, everlasting absolute substance like Self, Soul, or Atman within or without" - Rahula, p.39) and that if you can and do go deep enough, relativism wins, unequivocally.
For practical, day-to-day operation, pragmatism often wins, but only if you allow arguments that restrict your context.
Also, in my opinion, we don't define the rules in math, we discover them.
Here is the real mind blower: As much as we will structure and codify, even with ALL the data we will not reach logical consistency on everything. Building systems with that end will ultimately fail.
Yes, I have seen that illustration. What holds the balls to the fabric? Looking at the picture you automatically assume that GRAVITY pulls them down. But gravity is what the picture was supposed to explain. It is circular reasoning, using gravity to explain gravity.
It's called a transformer. The theory is that a changeing current causes a magnetic field to expand or contract, and the moving field will induce a current into any conductor it moves across. But if the wires are wound on a toroid (iron donut) all the field is inside the toroid and none can be detected moving around the wires. So the theory is wrong, but it works exactly as if the theory were right. And nobody knows what it does instead.
This is nonsense. There certainly is a magnetic field arbitrarily close to the wires, on the interior of the torus. That doesn't contradict any theory; it is a prediction of Maxwell's equations regarding how magnetic fields induce currents in wires.
That illustration has nothing to do with general relativity; GR does not actually appeal to "balls rolling down fabric", and it does not posit any force "outside" of spacetime. Rather, GR says that objects move in straight lines when not subjected to external forces — just like Newton. The difference is that GR allows spacetime to be curved, so straight lines can intersect along with other non-Euclidean behavior.
I think Newton's laws are precise within 99.95%.
Well, they are (up to about 0.6 c, at least,) but that's not the point. Indeed, the disparity between expected and measured data is less than 0.01%, which is also specifically mentioned in both the writeup (phrased as the measurement ratio and posited as 1:1.001) and in the article.
99.95% of what?
The ±0.05% refers to the accuracy of the measurement used to glean the data, and has nothing to do with the theory or the difference between the expected and measured value. They're codifying the error tolerance of the pulsar measurement.
StoneCypher is Full of BS
Maybe I don't know about the "Cartesian method of doubt", but it doesn't have anything to do with physics.
Uh, yes it does. The Cartesian Method for Doubt was introduced by Reneé Descartes as a method for seperating expectation from measurement when learning to interpret experimental data (as well as existentialism and skepticism as worldviews tolerant of "false senses.") Rule of thumb: if you don't know what something is, don't contradict the person talking about it. Even if it sounds incorrect, it might actually be correct.
Are you saying that if I measure something with a ruler, I should throw in a couple extra percentage points to the error calculation because I'm not sure if the universe exists?
Wow, you gave a dramatically oversimplified and openly absurd interpretation of something in order to discredit it. Impressive. No wait, that other thing: tedious. Yes, you should add a few hundredths of a percentage point to the error tolerance for a ruler, in order to account for wear and tear, manufacturing error tolerance, material growth/shrinkage due to temperature, wood expansion due to wood absorbtion, and to that you're apparently a complete tool who isn't able to seperate expectation from actuality.
Even if I *should*, what percentage should I throw in?
You would have to give a non-retarded example in order to receive an answer.
StoneCypher is Full of BS
What they mean by "99.95% right" is not that there is a 99.95% probability that Einstein's theory is dead right, and correct, and a 0.05% probability that it is dead wrong.
Horseshit. The ±0.05% isn't about relativity at all. It's the precision of the measurement used to gather data from the star. What they're actually saying is "we have data which is accurate to ±0.05% and the data fits relativity."
StoneCypher is Full of BS
surity
Me fail english? That's unpossible! Hey Ranger Rick, try "certainty" next time.
StoneCypher is Full of BS
Maybe you could explain why the example is bullshit, for those less educated than you are? Y'know, 'cause I have coursework credits in both physics and logic, and I don't see it. Indeed I'm curious whether in fact it's there, or whether you're just some blowhard who wants to sound smart.
Whoever modded parent insightful should have a stick placed squarely into their left retina. Insightful doesn't mean "talks shit without discussing the reason therefor."
StoneCypher is Full of BS
Nothing. A ratio with only one component stated is explicitly in contrast to one. You might as well complain that x=y+4 should actually be written as (1x+0) = (1y+0)+4.
Not all coefficients must be visible.
StoneCypher is Full of BS
Things work as if Einstein was right, but there is no evidence that he was right.
To me this just seems like a play on words. Observation is the only way in which we can test the validity of a model. If the model fits experimental data consistently and throughout a large number of experiments, we can only conclude it is right -- at least until someone makes an experiment whose results disprove it, but that's part of the nature of a scientific theory.
The point grandparent was getting at is that scientists never "decide something is right," but rather say "this theory matches data to within a tolerance of ± whatever%." And, in context, not only is grandparent correct to point this out, but what he's saying is very important to keep in mind. It's a pity he's not a better writer.
What is germane is that we never ever ever say "this model is correct" in any non-abstract scientific field. For any reason. Ever.
StoneCypher is Full of BS
Okay. I agree with what you say and apologise if my post sounded otherwise. But the impression I got from the original poster was that he somehow expected science to give definitive, not-to-be-ever-changed answers -- something that is far too common nowadays when laymen point the finger at scientists.
Score: i, Imaginary
[quote] General Relativity Is At Least 99.95% Right [/quote]
.05 % due to observational error .
It could also be argued that the test measurements off by
http://en.wikipedia.org/wiki/Measurement_error
What he said.
-Clio
Karma: Bad (mostly from not giving a fuck)
Blog: http://clintjcl.wordpress.com
Hmmm... doesn't have quite the same ring to it.
;-)
And oh, my bad, that's special relativity, not general relativity
one thing i never quite saw clarified is why scientists deduct that time warps just because a time-measuring device measures time differently under different conditions. couldn't it be that whatever underlying mechanism slows down or accelerates, while time itself ticks at the same rate? and how could you even see the difference?
Theories are generalizations about systems. Some generalizations are better fits to realty than others.
The clearance system sounds logical. It is not. It is completely arbitrary. -- John Bolton