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Lab Tuned to Gravity's 'Ripples'

Hemos posted more than 8 years ago | from the what's-the-frequency-kenneth dept.

173

Krishna Dagli writes "One of the great scientific experiments of our age is now fully underway. Success would confirm fundamental physical theories and open a new window on the Universe, enabling scientists to probe the moment of creation itself. The experiment is trying to detect ripples created in the fabric of space-time that sweep out from merging black holes or exploding stars and detection would be a final test of Albert Einstein's General Theory of Relativity. "

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173 comments

finally (0, Offtopic)

StanVassilevTroll (956384) | more than 8 years ago | (#15604743)

gravity waves create a first post.

Re:finally (0, Offtopic)

chunky shit salsa (956359) | more than 8 years ago | (#15604758)

heeeeey. how about some spicy salsa with that first post?

Space Core Directive 34124 (0, Offtopic)

tehgimpness (984446) | more than 8 years ago | (#15604766)

"No officer with false teeth should attempt oral sex in zero gravity."

sooo cold out in space (1)

a11 (716827) | more than 8 years ago | (#15604770)

Gravity's 'Ripples'? More like Gravity's Nipples.

Re:sooo cold out in space (-1, Offtopic)

ifuckyoutroll (956363) | more than 8 years ago | (#15604795)

My ass is in tune with Gravity's Ripples.
I fuck you.

negative outcomes? (3, Interesting)

m874t232 (973431) | more than 8 years ago | (#15604834)

What are the alternative models if gravity waves simply don't exist?

It's important to have alternative hypotheses, among other reasons, in order to be able to determine when you got a null result. Until the theoreticians have done their homework and provided a reasonable and plausible alternative hypothesis, perhaps we shouldn't be investing millions of dollars (euros) in these kinds of experiments.

Re:negative outcomes? (3, Insightful)

Anonymous Coward | more than 8 years ago | (#15604868)

Of course we should be investing in this technology. Even if it does cost us millions, nay even billions. Gravity is the single most important universal effect, and the sooner we know what it is, and how to manipulate it the better. A few billion upfront for that sort of tech is peanuts.

If the research doesn't pan out, then we will move on and create new hypothesis. You can only throw so much money at one thing at a time. If we fail, we redo.

just imagine the possibilities. Flying car anyone?

Baz

Re:negative outcomes? (1)

JensR (12975) | more than 8 years ago | (#15605025)

just imagine the possibilities. Flying car anyone?
Think bigger: Anti-Gravity-Sex !

Re:negative outcomes? (1)

LordVader717 (888547) | more than 8 years ago | (#15605053)

These guys [wikipedia.org] will sure like it.

Re:negative outcomes? (1)

Splab (574204) | more than 8 years ago | (#15605475)

You know, that might just be it, get the porn industry involved - they would have it figured out in no time.

Re:negative outcomes? (1)

mkw87 (860289) | more than 8 years ago | (#15606419)

Think of where you posted this.....you just confused the masses.

Re:negative outcomes? (5, Insightful)

mwvdlee (775178) | more than 8 years ago | (#15604883)

Plausible alternative hypotheses are nice to have, but shouldn't be a requirement for the simple reason that there might not be any plausible alternatives. Or at least none concievable with current knowledge, thus further necessitating the gathering of scientific proof as it can show whether you're missing some vital piece of knowledge.

let me be more precise (1)

m874t232 (973431) | more than 8 years ago | (#15605459)

Your argument is predicated on the assumption that we learn something from this experiment, but I don't think we do.

If the outcome is positive, it just confirms all existing theories (but likely won't be compelling enough to do so beyond reasonable doubt), and if the outcome is negative, we simply assume that the detection threshold wasn't good enough.

So, I agree that confirmatory experiments are important, but this one just doesn't seem to be a good one.

Re:let me be more precise (3, Informative)

Open_The_Box (620252) | more than 8 years ago | (#15606579)

OK. I wasn't going to get involved in this thread, but I really have to jump on that one.

It's not just about confirming Einstein's theory of general relativity. Or, in fact any of the other relativistic gravitational theories - most (if not all - been a while since I checked on the basic theory and they might have come up with some new ones) of which require the existence of gravitational waves. It's not simply a case of checking that the theory is correct - there are indirect measurements which have already done this, it's about directly detecting something we're sure is there. Don't get me wrong; in part, you're correct - if the outcome is negative, then we can set an upper limit (i.e. the waves must be of lower magnitude than X at frequency Y). This in itself allows corroboration with cosmological models and provides a valuable experimental check against predictions of numerical relativity such as the strain effect on space due to the merger of black holes.

But when a positive detection is made it will provide confirmation/empirical data on the processes involved in such violent astronomical phenomena. What are the physical processes involved in the inspiral of a binary system? Do pulsars with asymmetrical mass distribution really lose energy as gravitational waves? We know about the cosmic microwave background, what about the gravitational wave stochastic background?

It's not just a case of "There's a peak on the trace! Well, that's our job done! Who's for tea and biscuits?" The potential gains in knowledge of astronomy, astrophysics and even particle physics are vast. Not to mention the gains in laser technologies, control systems, material science and computational analysis that such a project brings. Just by designing and building these instruments we push the boundaries of what's known. Of course there will still be tea and biscuits (well, maybe beer and doughnuts) but that's half the fun right there.

OK. Rant over. Everyone back on your heads.

Re:let me be more precise (1)

m874t232 (973431) | more than 8 years ago | (#15606871)

Not to mention the gains in laser technologies, control systems, material science and computational analysis that such a project brings.

Those gains would be even greater if we invested directly in those areas.

if the outcome is negative, then we can set an upper limit (i.e. the waves must be of lower magnitude than X at frequency Y)

We have had half a dozen experiments trying to detect gravity waves, all with negative or indeterminate outcomes. And I note that neither you nor anybody else in this thread has provided a compelling argument why this experiment should be any different. How many billions of dollars are to be sunk into these kinds of fishing expeditions?

The potential gains in knowledge of astronomy, astrophysics and even particle physics are vast.

Until physicists get their house in order, I think large scale experimental physics like this (gravity wave detectors, particle physics, fusion) should get defunded. There are enough areas, both within physics and outside physics, that have yielded far more tangible scientific (not to mention, practical) results and that would use funding far more effectively.

Re:let me be more precise (2, Insightful)

Open_The_Box (620252) | more than 8 years ago | (#15607067)

But we do invest in these areas. How do you think you get a gravitational wave detector in the first place? They don't build themselves you know. And aside from this, you need to have reasons to investigate (and therefore invest) in these technologies - this is an example of a large scale project which has the potential for practical and tangible gains in (as I posted before) laser technologies, control systems, material science and computational anaylsis. These are tangible scientific results in their own right with several industrial applications and assorted spin-off tech companies.

As to how many billions of dollars it takes - quite a lot. But the practical outcomes I've listed are what you get. Along with international co-operation - many countries working together for a common goal.

And another thing. It's gravitational wave detection. Not gravity wave detection, which is something completely different.

Large scale experiments are what research is all about. There comes a point in research where a table-top experiment just won't do.

Re:let me be more precise (2, Interesting)

m874t232 (973431) | more than 8 years ago | (#15607281)

And aside from this, you need to have reasons to investigate (and therefore invest) in these technologies - this is an example of a large scale project which has the potential for practical and tangible gains in (as I posted before) laser technologies, control systems, material science and computational anaylsis. These are tangible scientific results in their own right with several industrial applications and assorted spin-off tech companies.

To the degree that the spin-off applications are valuable, the spin-off applications themselves will drive the development of the technologies, which can then (in a few decades) be used to conduct the physics experiments at a much lower cost. If the potential spin-offs don't justify investment in the technologies, then your justification that these are economically valuable is bogus.

As to how many billions of dollars it takes - quite a lot. But the practical outcomes I've listed are what you get. Along with international co-operation - many countries working together for a common goal.

Strange as that may be for you to believe, but people don't just collaborate internationally on big physics projects, and useful spin-off technology doesn't just come from big physics projects (and I suspect that dollar-for-dollar, large scale physics projects are one of the least productive projects when it comes to valuable spin-offs).

So, compared to this experiment, many other projects that could be funded with this money not only yield all the practical benefits you list, but in addition have a clear, predictable, and demonstrable scientific benefit no matter what the outcome of the experiment.

Large scale experiments are what research is all about.

I guess according to you, the the millions of researchers in the world that make do with small budgets just aren't doing real research; it's only when you have figured out how to milk the taxpayers out of a few billion dollars for a single experiment that you graduate to real research, right?

There comes a point in research where a table-top experiment just won't do.

We have funded these kinds of experiments for decades, all with negative outcomes. So, there also comes a point at which investing ever more in the same kind of large-scale experiment that yield no results won't do anymore. It seems to me that we have reached this point when it comes to direct detection of gravity waves.

Therefore, again, my question: what's the justification for doing this particular experiment, where previous experiments have failed? Simply saying "it has more sensitivity" isn't good enough--you need to explain why this level of sensitivity should be good enough when the same kind of experimentalists previously argued that the previous level of sensitivity ought to have been good enough then.

And another thing. It's gravitational wave detection. Not gravity wave detection, which is something completely different.

I think you're smart enough to figure out which of the two (valid) senses of "gravity wave" I'm using (and if you have ever bothered to read the original papers, you'll understand why this ambiguity is unlikely to go away even in English).

Re:let me be more precise (1)

jkauzlar (596349) | more than 8 years ago | (#15607201)

From the parent post:
The potential gains in knowledge of astronomy, astrophysics and even particle physics are vast. Not to mention the gains in laser technologies, control systems, material science and computational analysis that such a project brings.

It's important to invest in such technology for just this reason. The space shuttle, the moon landing, the Higgs-Boson experiments, etc are not just virtuosic feats or symbols of our technological growth, but they provide the means of refining the technology involved and solving smaller problems along the way. I can't think of any specific examples except for Tang, but I imagine the space shuttles have contributed far more to the average everyday experience of human life than just photographs of the earth from space. Sophisticated national defense is an enormous product of such otherwise useless experiments. Computers themselves were once mind-bogglingly expensive laboratory experiments with few practical applications, as were most of the high technology we see around us.

The early experiments in quantum mechanics eventually became applicable to very small-scale microprocessor technology. Einstein's theories-- well, umm, you know.. But you see my point-- the fact that light bends in space leading to the technology which clinched us the second world war? Pretty remarkable.

Re:negative outcomes? (1)

sconeu (64226) | more than 8 years ago | (#15605492)

Exactly. Before Planck, there wasn't any "plausible alternative hypothesis" to solve ultraviolet catastrophe. In that situation, what we simply say is "we dont' have a good theory to explain this... yet."

Re:negative outcomes? (1)

Ohreally_factor (593551) | more than 8 years ago | (#15605661)

Bah. The Hanso Foundation [thehansofoundation.org] has already been conducted research like this for years.

Re:negative outcomes? (1)

m874t232 (973431) | more than 8 years ago | (#15606889)

The difference is that the photoelectric effect didn't take multi-million dollar installations to demonstrate.

The question is and remains whether this particular experiment is a sensible use of scarce research dollars at this time, in particular since the same kind of experiment with the same promises has been carried out multiple times before.

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15607076)

The question is and remains whether this particular experiment is a sensible use of scarce research dollars at this time, in particular since the same kind of experiment with the same promises has been carried out multiple times before.

You are confused. Gravitational wave detectors are not being built to prove that gravitational waves exist. We already have strong evidence of that (see the 1993 Nobel Prize). They are being built to observe astrophysical phenomena, like radio telescopes, and to probe the strong-field regime of general relativity.

There have not been any other instruments like these built before that were even remotely capable of achieving those goals; even the current generation of LIGO may not be able to achieve them.

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15607320)

We already have strong evidence of that (see the 1993 Nobel Prize).

No, sorry, that's not evidence of the existence of gravitational waves, it's merely an observation that is consistent with their existence; there are other possible explanations.

Re:negative outcomes? (5, Insightful)

TheChrisMan (982990) | more than 8 years ago | (#15604892)

"It's important to have alternative hypotheses"

Is it? If I remember correctly the lack of an alternate hypothesis when Michelson and Morley failed to detect the aether caused Einstein to beging pondering special relativity.

Re:negative outcomes? (-1, Flamebait)

Anonymous Coward | more than 8 years ago | (#15604907)

You remember that far back? You must be old, son. Why you posting on /. when you should be gumming your oatmeal? Back to the nursing home for you extremely old man.

wrong (1)

m874t232 (973431) | more than 8 years ago | (#15605434)

MM was an experiment to measure a specific quantity, and it was clear that the quantity could be measured with that apparatus. As soon as the measurement was performed, there was no issue of detection thresholds: whether the measured speed was 0 or 10^-3 m/s, either way presented a problem for the classical theories.

Gravity wave detection is not at all analogous to that, since a negative outcome in this experiment still doesn't really tell you anything.

Re:negative outcomes? (1)

carnivore302 (708545) | more than 8 years ago | (#15605682)

Nope, it is unsure Einstein even heard of the experiment at the time he wrote his famous paper.

Re:negative outcomes? (2, Insightful)

ScentCone (795499) | more than 8 years ago | (#15604924)

This is the alternative model. The rest of us know that such waves actually propogate via infinitely long strands of pasta [venganza.org] .

But seriously - if things all point to a likely model, and nothing (rationally) points to an alternative, why kill yourself (and your budget) documenting hollow alternatives just so that you're sticking to academic form?

Re:negative outcomes? (1)

jcorno (889560) | more than 8 years ago | (#15604940)

Why does there need to be an alternative hypothesis if there's a chance the first hypothesis is correct? It's not like this would be the first experimental confirmation of general relativity.

And a null result is easy. All you need is the absence of gravity waves when you observe an event (like a collision of stars or black holes) that should produce them.

Re:negative outcomes? (1)

m874t232 (973431) | more than 8 years ago | (#15606946)

And a null result is easy. All you need is the absence of gravity waves when you observe an event (like a collision of stars or black holes) that should produce them.

Unfortunately, it isn't easy. We have had multiple experiments like this, all quite expensive, and all of them failed to demonstrate gravity waves. Physicists still believe that gravity waves exist but we just need a bit more sensitivity to detect them. That's a reasonable belief, but the question is whether that kind of belief should be enough to finance these kinds of experiments right now, or whether we should simply wait until either theory or experimental techniques have caught up.

It's not like this would be the first experimental confirmation of general relativity.

You can't confirm hypotheses, you can simply fail to disprove them. General relativity has survived a number of experimental tests, but so have an infinite number of alternative hypotheses.

Why does there need to be an alternative hypothesis if there's a chance the first hypothesis is correct?

Because otherwise you can't interpret the results. As I was saying, there have been attempts to detect gravity waves, and they failed to measure them. So, without an alternative hypothesis, you simply don't know: is this because they don't exist? Are they too weak? Are there other possibilities?

None of that matters if you're talking about cheap table-top experiments. But these kinds of experiments are expensive, and other science isn't getting done because these experiments are getting funding.

Re:negative outcomes? (2, Interesting)

Anonymous Coward | more than 8 years ago | (#15607151)

None of that matters if you're talking about cheap table-top experiments. But these kinds of experiments are expensive, and other science isn't getting done because these experiments are getting funding.

This is a common fallacy. I heard it a lot back in the SSC days. When the SSC was cancelled, did all of that earmarked money go to other physics? No. In reality, much of the funding for these large physics experiments is created specifically for those experiments, and would not exist otherwise.

In the case of LIGO, there was a sacrifice, however: gravity theory is somewhat less funded than it once was. Many leading gravitational physicists were consulted on this matter back when the funding for LIGO was being debated. The consensus of the community was that yes, this experiment is worth doing, even if gravity theory takes a hit

Speaking as someone who has worked in gravity theory, I think LIGO is a necessary experiment, even if it comes at the expense of some theory. There is no question of "waiting for the theory or experimental technique to catch up". Theory has gone about as far as it can without additional experimental input: there are lots of alternative gravity theories lying around, they are just currently indistinguishable from GR without better data. And the technology to build a working LIGO can't be developed from thin air: the advanced LIGO (LIGO II) experiments could not have been designed without doing LIGO I first. We have the technology now: we simply can't engineer it into a working instrument without testing it for real.

Re:negative outcomes? (2, Insightful)

insanarchist (921436) | more than 8 years ago | (#15604972)

Yes, let's be absolutely sure we're correct before testing a hypothesis. After all, what are hypotheses for?

Re:negative outcomes? (1)

andylievertz (687492) | more than 8 years ago | (#15605468)

Hypotheses only create more questions, according to Phaedrus.

Re:negative outcomes? (1)

m874t232 (973431) | more than 8 years ago | (#15607061)

Yes, let's be absolutely sure we're correct before testing a hypothesis. After all, what are hypotheses for?

What I'm saying is: when we invest a lot of money in an experiment, let's be sure we understand how the experiment and its possible outcomes relate to the hypothesis, and why similar previous experiments have failed. Just doing open-ended experiments without a prior understanding of what the possible outcomes mean is not doing science, it's voodoo or alchemy.

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15607251)

when we invest a lot of money in an experiment, let's be sure we understand how the experiment and its possible outcomes relate to the hypothesis, and why similar previous experiments have failed

Yeah, because none of the world's leading physicists ever thought to do that before asking for a billion dollars in funding.

I rather think you should go read some of the original LIGO planning documents.

Re:negative outcomes? (5, Interesting)

Tim C (15259) | more than 8 years ago | (#15604984)

It's important to have alternative hypotheses, among other reasons, in order to be able to determine when you got a null result. Until the theoreticians have done their homework and provided a reasonable and plausible alternative hypothesis, perhaps we shouldn't be investing millions of dollars (euros) in these kinds of experiments.

That's simply not true. Right now, all our understanding of how the universe works points towards the existence of gravity waves. If we fail to detect them, then one of two things is true:

1) The equipment was wrong
2) The theory was wrong

Until such time as it looks like 2) is the case, there's no basis for exploring alternative hypotheses, especially given that so far, we have no reason to doubt the current one and every reason to believe that it's either valid, or very nearly so.

As for needing an alternative to be able to recognise a null value, that's not the case either. The current theory makes a prediction. If we don't make an observation that matches prediction within expected tolerance and we can find nothing wrong with the equipment, then the theory is most likely wrong. At that point, you can bet your life that people will be scrabbling to work out how, and what needs to be done to correct (or replace) it.

Think of it this way - what if the theory is correct, and there simply *isn't* any "reasonable and plausible alternative hypothesis" (perhaps because we can't think of any, perhaps because there simply aren't any). Should we *never* attempt to confirm it?

Re:negative outcomes? (1)

Ana10g (966013) | more than 8 years ago | (#15605113)

Think of it this way - what if the theory is correct, and there simply *isn't* any "reasonable and plausible alternative hypothesis" (perhaps because we can't think of any, perhaps because there simply aren't any). Should we *never* attempt to confirm it?

Isn't this how religions get started?

Re:negative outcomes? (1)

AvitarX (172628) | more than 8 years ago | (#15605439)

But the theory is falsifiable.

The religion is started if not new theories are developed i this one proves false. The daa gathered as it disproves gravity waves may even be key to the new theories. To come up with a new theory that matches our observation but excludes gravity waves for no good reason sounds like fringe science to me.

Re:negative outcomes? (1)

m874t232 (973431) | more than 8 years ago | (#15607014)

Until such time as it looks like 2) is the case, there's no basis for exploring alternative hypotheses,

"The equipment is wrong" is an alternative hypothesis, albeit not a fully formulated one.

What is happening right now is that, after a number of these experiments have been done in the past and failed to demonstrate the existence of gravity waves, the people involved just say "hey, it didn't work, maybe our equipment wasn't sensitive enough/faulty, so we're just going to try again".

Think of it this way - what if the theory is correct, and there simply *isn't* any "reasonable and plausible alternative hypothesis"

I believe gravity waves exist, but people have failed to detect them in previous experiments. So, that means that either the previous experiments were insufficient to test the theory, or people don't understand the theory enough to make testable predictions. Either way, either people screwed up on the previous experiments, or they screwed up on the theory. The point is that until people have figured out which of the two is the reason previous experiments came up negative, it is difficult to justify funding expensive experiments.

Therefore my question: what are the alternative hypotheses? Another way of putting it is: how do you account for the fact that previous experiments designed to test for the existence of gravity waves didn't find them? Or, more succinctly: before we fund any more of this, we need to know how previous experimenters screwed up.

I note that nobody in this thread has given a satisfactory answer; everybody just waves their hands about how nice it would be to find them, and how it is important to identify them, both of which I agree with. But those are not sufficient reasons to conduct this experiment in light of what we already have done and what we know.

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15607222)

I believe gravity waves exist, but people have failed to detect them in previous experiments. So, that means that either the previous experiments were insufficient to test the theory, or people don't understand the theory enough to make testable predictions.

Very few people expected that the preceding experiments would see anything. They were performed because (1) without performing them, you cannot improve the technology, (2) there was the off chance that some really huge event might occur, (3) they were cheaper, and (4) the theory wasn't as well known, so the bounds on what the detectors could see weren't as tight.

We now have a much better handle on the gravitational wave bounds. (In fact, the bounds set by the earlier "failed" experiments were instrumental in improving our theory.) We can now calculate with reasonable confidence that LIGO I is within an order of magnitude of the sensitivity needed to detect gravitational waves. We have never before been able to make predictions of that accuracy. That's why the go-ahead was given on building LIGO.

In point of fact, it is quite likely that LIGO I will fail to observe gravitational waves: its sensitivity is borderline. This was known before the project started. It was built anyway, because only in building it could LIGO II be developed, which is the real experiment. If LIGO II doesn't see them, then you can't just attribute that to failed experiment or a misestimate of what waves should be out there: it will mean something's wrong with our theories of gravity.

I note that nobody in this thread has given a satisfactory answer; everybody just waves their hands about how nice it would be to find them, and how it is important to identify them, both of which I agree with. But those are not sufficient reasons to conduct this experiment in light of what we already have done and what we know.

That's not the reason LIGO was conducted. LIGO is being conducted to do gravitational wave astronomy, not just prove the existence of gravitational waves. We already have convincing proof of that.

Re:negative outcomes? (5, Interesting)

LordVader717 (888547) | more than 8 years ago | (#15604999)

Try this [wikipedia.org] . The experiment is strikingly similar to the Michelson-Morley interferometer, an experiment which also returned a null-result, trying to detect an "aether" for electrmagnetic waves.

The problem with these kinds experiments though is that results are very easily misinterpreted, because we really have no, shall we say, "creativity" in our imagination about such fundamental physics.

The Sagnac-interferometer (which BTW I will be building for a project) seemed to prove the presence of the aether that the Michelson-Morley experiment couldn't detect. It turned out to be a misinterpretation because they didn't quite grasp the concepts. (It turned out to be very useful anyway, as it's the basis for laser-gyroscopes)

This makes experiments like this even more important because if you are to accept any theories as "confirmed" or develop upon them, you need to research every possible result and implication.

Re:negative outcomes? (2, Interesting)

budgenator (254554) | more than 8 years ago | (#15606500)

I must be dense and you seem to know what your talking about; FTA I see a schematic of a device that would be very accurate in measuring minute differences in distance and time. Presumably a Gravity wave would distort time-space consistant with the lorentz transformations, which I think I understand, what I don't understand is since the time-space distortion would apply to the instruments frame of reference, wouldn't they get the same null-results that the MM experiment got?

Re:negative outcomes? (2, Informative)

Open_The_Box (620252) | more than 8 years ago | (#15606777)

Technically, you're correct. If the distortion of space-time 'compresses' one arm of the interferometer and 'extends' the other in a step (or constant offset), the amount of time taken for the light to traverse the arms and recombine at the beamsplitter wouldn't change and no phase difference would be detected between the returning beams.

However, gravitational waves are not stepwise events and have a frequency. This means that if the beams are split and traverse the arms the 'compression/extension' experienced by the beam on the way out will have changed by the time the beam returns such that the frame of reference is different for the outgoing and incoming beam in each arm. In essence, the instruments detect 'changes' in space-time but are unable to measure static states.

The schematic you mentioned from the article has additional mirrors [e + f]. 'f' is the signal recycling mirror which allows the instrument to by optically 'tuned' to the frequency of optimal detection (i.e. the frequency of your expected gravitational wave event). That's not to say that by choosing one frequency you're ignoring all the others - it just means the device is more sensitive at one chosen frequency.

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15605076)

Right now, there aren't really any alternatives. The consistency of a gravity theory with special relativity logically requires the existence of gravitational waves, as far as anyone has been able to ascertain. (Basically, changes in a gravitational field have to propagate at light speed, and we call those propagating changes "waves".)

Now, it is quite possible that these experiments will not detect gravitational waves, because they're right at the limits of their sensitivity. If the next generation of detectors fails as well, then people may start having doubts (depending on how reliable they think the next generation is). But the bottom line is, the absence of gravitational waves is so hard to account for theoretically that probably no one will come up with a credible theory without them without experimental data showing the way toward the new theory. (And not just "we don't see any waves", but more detailed probes of the way gravity behaves.)

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15605101)

Until the theoreticians have done their homework and provided a reasonable and plausible alternative hypothesis, perhaps we shouldn't be investing millions of dollars (euros) in these kinds of experiments.

Yeah, I'll bet they never thought about any of that. Damn scientists. They're also rushing around, throwing the unending flow of basic science research funding at pet projects, willy-nilly.

Re:negative outcomes? (2, Interesting)

sweetser (148397) | more than 8 years ago | (#15605147)

I've got an alternative, and it does EM too, being discussed here:

http://physicsforums.com/showthread.php?t=87097 [physicsforums.com]

The theory also predicts gravity waves, but the transverse modes of emission for a 4D wave are EM, and the longitudinale and scalar modes are the stuff of gravity. So GEM theory (gravity and EM) predicts that gravity waves will travel at the speed of light, but the polarization will not be transverse like GR predicts.

I think gravity MUST be viewed as a longitudinal wave, not transverse. Here's a thought experiment. You have a cup of neutrinos (see, this is a thought experiment because no such cup can be manufactured). You spill the cup. The neutrinos fall, and when they reach the floor, they keep falling, through the center of the Earth, to the other side, and in about 88 minutes, back to where they started, just to repeat the cycle again. This is a SHO (simple harmonic oscillator), with a period of 88 minutes, and a wavelength of twice the diameter of the Earth. The neutrinos are acceleration in the direction of velocity which is a defining characteristic of a longitudinal wave.

doug
TheStandUpPhysicist.com

Re:negative outcomes? (1, Insightful)

Anonymous Coward | more than 8 years ago | (#15605447)

I think gravity MUST be viewed as a longitudinal wave, not transverse. Here's a thought experiment.

Your thought experiment proves nothing. GR predicts that a "cup of neutrinos" will oscillate back and forth; it also unambiguously predicts that gravitational waves are transverse. Therefore, neutrinos oscillating back and forth is not proof that gravitational waves must be longitudinal; a counterexample exists.

More directly: your thought experiment has nothing to do with gravitational waves, it is only sensitive to static gravitational fields. Of course objects will accelerate in the direction of the gravitational field. This has nothing to do with whether the waves are parallel or perpendicular to their direction of propagation.

Note that if you did the same experiment with a test charge and a uniformly charged ball, you'd get simple harmonic motion, but electromagnetic waves are provably transverse: another flaw in your logic.

Re:negative outcomes? (1)

sweetser (148397) | more than 8 years ago | (#15605906)

The question for me is whether GR is logically consistent on polarization. I know that gravity waves like the ones being hunted for here arise from the "water balloon" kind of motion for an isolated source (a quadrupole moment, no dipoles allowed). And GR predicts that the wave emitted will be transverse.

A simple harmonic oscillator is described by a few things: its period, its wavelength, and its polarization. As you correctly point out, the neutrinos are a different animal from the gravity waves generated by an isolated source, but both have the same cause, gravity. Nature likes to be logically consistent, so the I think the longitudinal SHO for the static gravitational field will also appear as a longitudinal gravity wave for a dynamic gravity field.

If you vibrate an electron back and forth say by heating it up in a light bulb filament, it will emit a photon perpendicular to that motion. EM is a transverse wave every way it is generated, no exceptions. To be logically consistent, I argue that gravity is a scalar or longitudinal wave, no exceptions. My proposal says EM is a transverse, spin 1 field, and gravity is longitudinal/scalar, spin 2 field, both of which travel at the speed of light.

doug

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15606023)

The question for me is whether GR is logically consistent on polarization.

Yes, it is. Go work through the derivation.

Nature likes to be logically consistent, so the I think the longitudinal SHO for the static gravitational field will also appear as a longitudinal gravity wave for a dynamic gravity field.

Doug, go back and study what longitudinal and transverse waves are. Whether a particle moves back and forth is independent of whether the waves it generates are transverse or longitudinal.

For instance, as I already pointed out, a charged particle moving in SHO due to an external electric field will not emit longitudinal electromagnetic waves. There is no reason why it should emit longitudinal gravitational waves either.

To be logically consistent, I argue that gravity is a scalar or longitudinal wave, no exceptions.

There is nothing to be consistent with. SHO does not logically imply longitudinal waves.

My proposal says EM is a transverse, spin 1 field, and gravity is longitudinal/scalar, spin 2 field, both of which travel at the speed of light.

Spin 2 fields cannot be scalar; by definition, they are tensor.

You know, 10 years ago I used to read all your quaternion posts on Usenet. I thought they were a rather quixotic "if all I've got is a hammer, everything looks like a nail" effort, but interesting. It's saddening to see the depths of crankdom into which you've sunk. I have no idea how you can sling around differential geometry and hypercomplex numbers and still not understand basic undergraduate physics like "how are longitudinal and transverse waves made".

Re:negative outcomes? (1)

sweetser (148397) | more than 8 years ago | (#15606703)

Clearly /. is not the best way to communicate physics. I said very clearly, EM waves are transverse, that there is no longitudinal EM wave, yet you appear to think that is what I said.

If you read about the Gupta/Bleuler method for quantizing a 4D wave equation, they talk about 4 modes of emission: 2 transverse, one longitudinal, and one scalar. They are using the word "scalar" to describe the mode of emission, not in reference to tensors. If you are familiar with that approach to quantizing the EM field, it is the scalar mode of emission that would allow negative probabilities. Since that makes no sense, they use a "supplementary condition" to make the longitudinal and scalar modes virtual. What my proposal does is make those modes do the work of gravity, where like charges attract, due to a symmetric field strength tensor of a spin 2 field. EM is the spin 1 antisymmetric field strength tensor where like charges repel.

> SHO does not logically imply longitudinal waves.

I agree with that. Sound happens to be a longitudinal wave. The changes in air pressure occur in the direction it is moving. In my neutrino example, the neutrinos accelerate in the direction they are moving. That is why the neutrino SHO is a longitudinal SHO. This system, the neutrinos moving in a static g field, is a longitudinal wave. I think that is correct at the undergrad level.

No matter how you jiggle an electron, you will never make a longitudinal wave of light, the waves will always be transverse. What I argue is that no matter how one moves masses, it will never be a transverse wave. As Clifford Will wrote in his 100+ page review, if the data comes back to show that the gravity waves caused by the collapse of a dense source is NOT transverse, that would be a big challenge for general relativity. It would also be a piece of data in support of my rank 1 field theory. Fortunately, data will rule the day.

One reason I cut way back on posting to SPR is people decide to toss in negatives, when all I ever care about are the technical issues. I have a Lagrange density, field equations, solutions to the field equations, and experiments like the one discussed in this thread, all plugged through Mathematica. In a measurable way - there are two experiments to test the validity of my proposal, the other being light should bend 0.7 microarcseconds more around the Sun than GR predicts - the GEM theory is a better formed alternative to GR than all of string theory at this time.

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15607015)

I said very clearly, EM waves are transverse, that there is no longitudinal EM wave, yet you appear to think that is what I said.

No. What you said is that because a SHO due to gravity exhibits linear oscillatory motion, the waves produced by that SHO should be longitudinal. We both know that is not true in general: the electromagnetic case is an example. Therefore, your logic claiming that this should be true in the gravitational case is wrong: there is no logical requirement that linear motion in a SHO should have anything to do with whether the wave is longitudinal.

In my neutrino example, the neutrinos accelerate in the direction they are moving. That is why the neutrino SHO is a longitudinal SHO.

However, that does not imply the generation of longitudinal waves. If you construct a SHO out of charged particles in an electrically charged ball, the test particles will accelerate in the direction they are moving. But the electromagnetic waves radiated are not longitudinal.

There is no difference between your neutrino thought experiment with gravity and my charged particle thought experiment with electromagnetism, as far as your argument is concerned. Your argument concerns only the direction of acceleration and claims to infer something about the polarization of the waves. My thought experiment proves that a "longitudinal SHO" need not produce longitudinal waves.

No matter how you jiggle an electron, you will never make a longitudinal wave of light, the waves will always be transverse. What I argue is that no matter how one moves masses, it will never be a transverse wave.

You have given no such argument. The only argument you gave applies equally well to electrons and light waves as it does to neutrinos and gravitational waves. It is false for the former and therefore flawed.

It would also be a piece of data in support of my rank 1 field theory.

Make up your mind. Is it a scalar theory, vector theory, or tensor? First you say it's scalar (rank 0). Then you say it's spin 2 (rank 2). Then you say it's rank 1 (vector).

Don't be too hasty to jump on anything in support of your theory. It is quite likely already falsified by existing experiment. There are already very heavy constraints on relativistic gravitational theories that are not transverse traceless.

One reason I cut way back on posting to SPR is people decide to toss in negatives

Yeah, it must be troubling when people keep telling you that you don't know what you're talking about. Better to go over and post to some physics forums where nobody knows GR.

I have a Lagrange density, field equations, solutions to the field equations

You don't even know if your theory is scalar or tensor. What do you know about interpreting its solutions?

Re:negative outcomes? (1)

sweetser (148397) | more than 8 years ago | (#15607266)

I hope we agree that sound is a longitudinal wave, and the EM is a transverse wave. The changing pressure in sound is in the direction of the traveling wave. The changing E and B field for light are transverse to the direction the light wave goes.

I'm ready to concede my logic was too simple. Part of the description of the sound field or the E and B fields must include the vectors for those fields. I would have to show that all the vectors that describe gravity all are colinear for the neutrino example. I beleive that to be true, but I did not show that, so you are correct in your critique.

Here is the rank of various parts of the theory.

        Rank 0: The Lagrangian
        Rank 1: The field equations, the source
        Rank 2: The asymmetric field strength tensor.

Exactly the same thing applies for EM. The classical Lagrange density is rank 0. The Maxwell equations can be writen as a rank 1 field theory. The field strength tensor for EM is an antisymmetric rank 2 tensor, F^uv.

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15607321)

Here is the rank of various parts of the theory.

Rank 0: The Lagrangian
Rank 1: The field equations, the source
Rank 2: The asymmetric field strength tensor.


You should call it a rank-1 (vector) theory, to be consistent with other usage.

There are severe restrictions on the tenability vector theories. See MTW (chapter 7) and the Feynman Lectures on Gravitation.

I would be very skeptical of any relativistic theory with a source of gravity other than rank-2 (the stress-energy tensor or some variation thereof).

Re:negative outcomes? (2, Insightful)

Bob3141592 (225638) | more than 8 years ago | (#15605225)

What are the alternative models if gravity waves simply don't exist?

There are already alternative theories, such as bosons named gravitons. That might just be a variation in interpretation of wave-particle duality, but since quantum gravity isn't the same thing as general relativity it passes muster. There are other gravitational alternatives proposed, usually flawed and/or not well accepted by the scientific community. And what impact this experiment wil have on the Higgs particle question, one way or another?

Your post seems to imply this is an all or nothing experiment. But GR wouldn't be challenged only by a null result. If the magnitude of any detected gravity waves is significantly different from expectations, the discrepancy will have to be explained. Often, these differences are more challenging to a theory. Unexpected behavior of a newly detected but predicted phenomena is also a major challenge to existing theories. I can't wait to see what kind of information can be obtained by some analog of Zeeman splitting in gravity wave spectroscopy, if such a thing exists. That will be far more revealing than any "Yup, that's a gravity wave" result.

Re:negative outcomes? (0)

Anonymous Coward | more than 8 years ago | (#15605234)

Well, the alternative depends upon how you wish to view the world. One simple explanation is that gravity is then a fundamental force that is capable of propogating at infinite speeds. This is the current way gravity works. That is, you tend to choose a point source (or convert an object to a point source at its center of mass) and draw a field for it. Such a simple model ignores the effects of other objects but is handy when you are examining, for example, the effect of gravity on a car driving on the earth's surface. That is, the effect of gravity from the moon, Jupiter, the Sun, and nearby trees all are negligible when compared to the earth itself.

Re:negative outcomes? (2, Informative)

rotenberry (3487) | more than 8 years ago | (#15605462)

Gravitational waves will exist in any theory of gravitation that requires the effect of gravity to propagate at a finite speed. Newton's theory of gravity assumes that the effect propagates at an infinite speed, so this theory does not predict gravitational waves.

It should be noted that the primary purpose of the detection of gravitational wave since at least the 1970's has been the both the detection and interpretation of the information contained in these waves. Depending on the frequency of the waves, they contain information about the beginning of the universe (long wave) or the collision of massive bodies (short wave). The advantage of a laser interferometer is that it is a wide band detector, while a Weber bar is a narrow band detector.

It was still being argued as late as the 1960's whether Einstein Theory gravatation waves could transmit energy:
http://en.wikipedia.org/wiki/Gravitational_radiati on [wikipedia.org]

Re:negative outcomes? (2, Funny)

metamatic (202216) | more than 8 years ago | (#15605489)

What are the alternative models if gravity waves simply don't exist?

Intelligent falling [theonion.com] . After all, gravity is just a theory.

Re:negative outcomes? (1)

steve_bryan (2671) | more than 8 years ago | (#15607243)

Who allowed you to operate a keyboard before you shook the cobwebs out of your head? Do you really thing Kip Thorne reads slashdot with his Wheaties in the morning to glean your wisdom from it? One of the dangers of articles that popularize science for the multitudes who can't be bothered to study enough to understand even approximately what is involved, is that some readers get the illusion that they actually know something. Just a hint, from what you've written it seems safe to infer you know approximately nothing which is not a problem. But deciding you should offer sage advice is somewhere between ludicrous and nauseating.

ripples in fabric of space-time? (0, Offtopic)

runlevel 5 (977409) | more than 8 years ago | (#15604843)

If this test is sucessful, what can be used with the information the scientists gain? It may become possible to predict future ripples, but the nature of such phenomena would suggest that they can't be avoided or blocked.

Re:ripples in fabric of space-time? (2, Funny)

necro81 (917438) | more than 8 years ago | (#15604877)

If this test is sucessful, what can be used with the information the scientists gain?
The development of warp drive capabilities, of course.

Re:ripples in fabric of space-time? (4, Interesting)

RocketRainbow (750071) | more than 8 years ago | (#15605063)

Runlevel 5 asked: "what can be used with the information the scientists gain?"

It would certainly explain the fact that there seems to be an upper limit on the rotational frequency of neutron stars (pulsars). Likewise, you can also expect to see gravity waves in the oscillation of large stellar bodies in collision, which might also give insight into gamma ray bursts.

One of the most interesting things we can do with gravity waves is look back beyond the cosmic microwave background and watch the early gravitational shape of the universe, perhaps detect a sort of cosmic gravity wave background. It's something we've never done before, so it's a sort of "let's see what we find when we turn this thing on" experiment - we could find all sorts of things about the shape and evolution of the universe which might in turn make a tremendous difference to the way we interpret earth-bound physics.

There is no danger from gravity waves and no apparent engineering purpose (not even warp drive) because they are astonishingly small - even a 4m long laser can't detect them (yet! - some technological improvements are on the way). This is because gravity is such a weak force that the only detectable gravity waves are caused by extremely massive bodies moving at extremely high speeds; even then, the strongest waves are easily able to dissipate to "nothing" before we would ever notice them. (In numbers, the best gravity wave LIGO could ever expect to see would cause the scientist's beautiful assistant to have her dimensions perpendicular to the wave oscillate at an amplitude of 10^-21m.) So it's not just a matter of understanding and engineering gravity waves, rather of using them to confirm or falsify key elements of our physical and cosmological theories.

Of course, theoretical physics has some interesting and wholly unexpected practical outcomes... Your computer uses quantum mechanical transistors - your webcam uses a quantum mechanical CCD (photoelectric effect) and medical tomography, using astronomical algorithms, continues to save lives.

Re:ripples in fabric of space-time? (1)

metamatic (202216) | more than 8 years ago | (#15605567)

There is no danger from gravity waves and no apparent engineering purpose (not even warp drive) because they are astonishingly small [...]

You could say the same about atoms, but I think the people of Hiroshima and Nagasaki would beg to differ.

Re:ripples in fabric of space-time? (0)

Anonymous Coward | more than 8 years ago | (#15605611)

A poor analogy. Atoms are very small, but they contain a large amount of energy. Gravitational waves carry very little energy (at least across astrophysical distances): that's the whole reason why we haven't detected them yet. Creating waves strong enough to detect requires hugely powerful processes such as the close inspiral of neutron stars. We will never be able to create waves like that ourselves without the ability to sling stars around — and if we can do that, the technological applications of (the much weaker) gravitational waves are likely to be moot.

Re:ripples in fabric of space-time? (0)

Anonymous Coward | more than 8 years ago | (#15605158)

The main application will be as a "telescope", analogous to radio telescopes but using gravity instead of electromagnetism. It won't have the imaging resolution of a radio telescope, but it will be able to detect signals that we couldn't otherwise detect (electromagnetic waves can be blocked by gas and dust), as well as probe the gravitational dynamics in strong fields near neutron stars and black holes.

Re:ripples in fabric of space-time? (0)

Anonymous Coward | more than 8 years ago | (#15607157)

Detecting gravitational waves would open a lot of doors and confirm many theories besides general relativity. For example it will confirm either the inflation/big bang scenario (witch predicts that there are "primordial" gravitational waves). If no "primordial" gravitational waves are detected it would confirm the brane clash scenario for the origin of the universe.

If we can detect those we can also explore the universe, much as we do with the electromagnetic spectrum but it will be more powerful, since gravitation does not gets absorbed ("gravitational wave astronomy")thus giving us access to matter that cannot be seen.

quality bleaching at cost (-1, Troll)

Anonymous Coward | more than 8 years ago | (#15604881)

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Moment of Creation (3, Funny)

Anonymous Coward | more than 8 years ago | (#15604889)

enabling scientists to probe the moment of creation itself
In other words, scientists will get a touch of His Noodly Appendage [flyingspag...onster.org] , and a bath in His Mighty Sauce.

Mmmmmm.. Ripples..... (5, Funny)

insanarchist (921436) | more than 8 years ago | (#15604912)

In later tests, the scientists plan to add sour cream and cheddar to the ripples in an effort to test gravity's potential for inter-galactic tastiness!

Eddies in the Space/Time Continuum (4, Funny)

Ohreally_factor (593551) | more than 8 years ago | (#15604946)

No, seriously, he is. Anyone have any idea on how to get him out?

Re:Eddies in the Space/Time Continuum (1)

TrekkieGod (627867) | more than 8 years ago | (#15605212)

I don't care if he gets out, I'm keeping his couch.

Re:Eddies in the Space/Time Continuum (1)

SEWilco (27983) | more than 8 years ago | (#15607053)

Dude, we're in it too. You go first.

Will they measure the speed of gravity as well? (3, Insightful)

master_p (608214) | more than 8 years ago | (#15604978)

Right now we are uncertain of the exact speed of gravity. Some measurements resulted in speed between 0.8 and 1.2 times the speed of light (according to this [wikipedia.org] ). If the speed of gravity is greater than the speed of light, does that violate the general relativity? There are many consequences.

It is important that we find what gravity is, because if it is a wave of particles, then maybe there is a possibility to find a way to shield gravity away. Shielding gravity would be a major step towards space exploration.
 

Not to mention (2, Funny)

maillemaker (924053) | more than 8 years ago | (#15605083)

How cool it would be to fly like superman. :)

Steve

Re:Not to mention (1)

weeboo0104 (644849) | more than 8 years ago | (#15605281)

Or train in several times the Earths gravity and finally become a Super Saiyan!

Re:Will they measure the speed of gravity as well? (5, Informative)

Anonymous Coward | more than 8 years ago | (#15605132)

Right now we are uncertain of the exact speed of gravity.

We are always "uncertain" about the exact value of any physical quantity, because no quantity can be measured with infinite precision.

There is very little doubt that the speed of gravity is equal to the speed of light.

Some measurements resulted in speed between 0.8 and 1.2 times the speed of light

The Taylor-Hulse pulsar measurements have measured the accuracy of that speed to within a few percent, much better than the 20% figure you cite. Furthermore, most of the gravitational physics community is convinced that the experiment mentioned did not measure the speed of gravity (as the Wikipedia article alludes to).

If the speed of gravity is greater than the speed of light, does that violate the general relativity?

Yes. It also violates special relativity and the laws of cause and effect.

It is important that we find what gravity is, because if it is a wave of particles, then maybe there is a possibility to find a way to shield gravity away.

Gravity being "a wave of particles" does not imply that it can be shielded, and gravitational wave detectors are unlikely to tell us anything about that issue.

Even if it were possible to "shield gravity" (very unlikely), it is almost certainly impossible to do it with any realistic technology, because we already have a thorough understanding of gravity on the scales that our technology can reach in the forseeable future.

A little realism: LIGO and its kin may teach us something new about gravity near neutron stars and black holes, but the most likely outcome is that it will simply serve as a telescope to probe astrophysical phenomena not detectable in visible light. It is very farfetched to think that it will lead to antigravity or any Star Trek type applications.

Re:Will they measure the speed of gravity as well? (1)

anshil (302405) | more than 8 years ago | (#15605481)

>>If the speed of gravity is greater than the speed of light, does that violate the general relativity?
>Yes. It also violates special relativity and the laws of cause and effect.

What about the tunneleffect, does it violate the laws of cause and effect?
If the electron tunnels through a barrier, at what speed does it tunnel?
There are mainly 2 possibilities:
* If it is instant it's greater than the speed of light.
* If it is not instant (for example speed of light) where the hell is it, when it vanished on one side until it appears on the other side.
* And if it only travels at the speed of light, since the electron with it's electric charge can never be INSIDE the barrier. Where is the charge when it does not travel instant, does this violate the symmetry of eletric charges?

Re:Will they measure the speed of gravity as well? (0)

Anonymous Coward | more than 8 years ago | (#15605583)

What about the tunneleffect, does it violate the laws of cause and effect?

No, because quantum tunneling cannot be used to transmit information of any kind faster than light.

* If it is instant it's greater than the speed of light.
* If it is not instant (for example speed of light) where the hell is it, when it vanished on one side until it appears on the other side.


This has nothing to do with quantum tunneling. You can apply the same argument to making a measurement of a quantum particle's position at one time, and making another measurement of its position at a slightly later time — its wavefunction extends throughout all of space. The existence of a potential barrier is irrelevant.

In quantum mechanics, a particle simply does not have a position in between position measurements; it is in a superposition of position eigenstates. Your question of "where is the particle in between measurements" is ill-posed in quantum theory.

Re:Will they measure the speed of gravity as well? (1)

internic (453511) | more than 8 years ago | (#15605635)

Excellent post. I only wish you'd made it while logged in so that I could look for your posts in the future.

Re:Will they measure the speed of gravity as well? (3, Funny)

exp(pi*sqrt(163)) (613870) | more than 8 years ago | (#15606008)

no quantity can be measured with infinite precision.
There is one apple on my desk. Not 0.99. Not 1.00002. Exactly one. I measured.

Re:Will they measure the speed of gravity as well? (0)

Anonymous Coward | more than 8 years ago | (#15606203)

That's due to a choice of definition more than anything else. There are astronomically many different assemblages of atoms all of which may be labelled "one apple" (and many more for which the number of apples may be uncertain), but that's not really what "making a physical measurement" means.

It reminds me of an Asimov anecdote in which he challenged a professor to give him one-half a piece of chalk. The professor broke the chalk in half and gave him a piece; Asimov replied that he had been given "one piece of chalk". Then the professor insisted that "one half" meant "one half of a regulation length piece of chalk", to which Asimov inquired whether he was sure it wasn't 0.48 of a length of a chalk.

Re:Will they measure the speed of gravity as well? (1)

infolib (618234) | more than 8 years ago | (#15606796)

There is one apple on my desk. Not 0.99. Not 1.00002. Exactly one. I measured.

Actually, due to quantum fluctuations there's all kinds of particles and their composites being created and annihilated at your desk at any moment. There is an extremely small but finite probability that an apple has come into existence since your measurement. (Or that there was actually two apples, but vacuum fluctuations interfered destructively with the photons signalling the existence of one of them). Given this small probability of having 0 or 2 (or 3 or 4 apples) you could try to model your uncertainty regarding the number as a Gaussian probability distribution having a very small but finite sigma. You now have 1+/- sigma apples.

I really wouldn't eat any apples arising from quantum fluctuations though. First of all you have no idea what they're made of, plenty of apple-resembling quantum fluctuations might be toxic. Secondly the apple would be the rarest and most exciting object in the observable universe, probably for our duration. Give it to the Smithsonian or something, even if the curator seems somewhat skeptical...

Re:Will they measure the speed of gravity as well? (0)

Anonymous Coward | more than 8 years ago | (#15605141)

Right now we are uncertain of the exact speed of gravity. Some measurements resulted in speed between 0.8 and 1.2 times the speed of light (according to this). If the speed of gravity is greater than the speed of light, does that violate the general relativity? There are many consequences.

TO clarify, the .8 and 1.2 numbers are the error margins. That particular experiment went a long way to confirming the speed of light as the upper constant (consistent with general relativity). I.e., the middle of the error margin is *the speed of light*.

Re:Will they measure the speed of gravity as well? (1)

node 3 (115640) | more than 8 years ago | (#15605157)

Shielding gravity would be a major step towards space exploration.
Not to mention a potential solution for our current obesity epidemic.

Yes, it's a dream I have. The dream to one day find myself in a situation where I can use the phrase, "bring in that floating fat man, the Baron!"

Re:Will they measure the speed of gravity as well? (1)

RocketRainbow (750071) | more than 8 years ago | (#15605247)

Yes, we can create anti-gravity stomach holder-uppers, navigate Guild ships through folds in space-time, even create invisible spaceships... but it's meaningless without a good religion and a good sniff of Melange.

Re:Will they measure the speed of gravity as well? (3, Funny)

flumps (240328) | more than 8 years ago | (#15605533)

... doesn't that rather pre-suppose two things?:

        1. The aforementioned Anti-gravity and

        2. That you will become important enough to know a Baron?

Both, I would say, are equally improbably but 2 perhaps slightly more so :P

Love the idea though rofl

Re:Will they measure the speed of gravity as well? (1)

r2q2 (50527) | more than 8 years ago | (#15605387)

If you read the wikipedia article it says that that variance is in line with current theoretical model's of general relativity.

Re:Will they measure the speed of gravity as well? (1)

steveo777 (183629) | more than 8 years ago | (#15605485)

It would be a major step in kung fu movies. No more wires, and you could finally pull off all those sweet moves at home.

Wow, I need to get laid (2, Funny)

Raleel (30913) | more than 8 years ago | (#15605189)

I really read that as gravity nipples. No, I don't know what a gravity nipple is.. maybe an inverse black hole or something. But by God, my lab would be tuned to them, that's for sure!

You can participate (5, Informative)

mike449 (238450) | more than 8 years ago | (#15605370)

I am surprised nobody mentioned Einstein@home - http://einstein.phys.uwm.edu/ [uwm.edu] .
This experiment uses distributed computing to process their results,
and you can participate.

uh.. about creation... (1)

NewToNix (668737) | more than 8 years ago | (#15605735)

"enabling scientists to probe the moment of creation itself."

It's the moment before that I want to know about... Oh, wait...

what if it cancels itself out? (1)

cyclomedia (882859) | more than 8 years ago | (#15605759)

If gravity waves cause spacetime to flex in a, er, wavelike fashion, then what if the wavelength of the light passing over those waves is also flexed? thus, as we and all our physical measuring equipment are also flexing then when a difference occurs the light, equipment and the field it's situated in flex too. So there will be nothing to measure. As in if you were trying to measure the expansion or contraction of a piece of metal due to a temperature change using a ruler constructed of the same metal as the one you are measuring. Geddit?

Re:what if it cancels itself out? (0)

Anonymous Coward | more than 8 years ago | (#15605917)

It's not the wavelength that's important so much as the time of flight for the photons: differences in the interferometer arm lengths due to spacetime curvature lead to different times of flight. You should note that the curvature of space is different in the two arms, producing effects that don't cancel out. If the length of both arms changed by exactly the same amount, then this interferometer wouldn't be able to detect that.

Question for a Physics Buff (1)

uniqueUser (879166) | more than 8 years ago | (#15605824)

After reading TFA, I have a question. Are there any physics buffs out there who can answer this? The article explains that the GEO 600 works by splitting a LASER beam with a semi-transparent mirror bla bla bla....

My question is this. What would happen if you shot photons at a semi-transparent mirror just one at a time. Can the exact number of photons that takes one route over the other be predicted? I assume that it should be 50/50 if the mirror is 50% transparent, but the likelihood of any given photon taking one route over the other should be random unless maybe if the mirror is polarized? If it can not be predicted, is this the limitation of accuracy for the GEO 600?

Re:Question for a Physics Buff (1, Informative)

Anonymous Coward | more than 8 years ago | (#15605895)

What would happen if you shot photons at a semi-transparent mirror just one at a time. Can the exact number of photons that takes one route over the other be predicted?

It can be predicted only statistically, in the sense that you can't predict the "exact" number of heads that you will get if you flip a coin N times.

I assume that it should be 50/50 if the mirror is 50% transparent, but the likelihood of any given photon taking one route over the other should be random unless maybe if the mirror is polarized?

It's random, and is 50/50 for a 50% transparent mirror.

If it can not be predicted, is this the limitation of accuracy for the GEO 600?

Uncertainty in the number of photons arriving at the detector is a limitation of the experiment's accuracy: it's called "quantum shot noise". However, that uncertainty would be present even without a mirror to split them. Perhaps the mirror exacerbates the effect.

Re:Question for a Physics Buff (0)

Anonymous Coward | more than 8 years ago | (#15606940)

Nope - each photon actually uses both paths...

Re:Question for a Physics Buff (1)

dltaylor (7510) | more than 8 years ago | (#15607231)

Waves, not particles, grasshooper. Interference (hence "interferometer") is a wave effect. This is an experiment where you do not try to see which way the photon went (which would collapse the wave), so, in very simplistic terms, it went both ways. The question is whether "both ways" took the same amount of time. If not, something differentally shortened, or lengthened, (depending on your point-of-view) the arms.

I do wonder if a "ripple" could resemble an acoustic compression wave and interact with the apparatus such that the "high-density" and "low-density" phases of the ripple lengthened then shortened the arms during the photon's flight time to provide a net "no-effect". Would depend on the wavelength of the ripple, I suspect.

Gravity Wave Generator - At Caltech (1)

QuantumFTL (197300) | more than 8 years ago | (#15606323)

True story: I was out at Caltech one summer, and was passing by the astronomy faculty lounge looking for a drink... I walked in and I noticed a curious contraption - it was rectangular, the size of a lunchbox (looked very much like a car battery charger, or power supply), but on the top it had a motor-driven bar with a metal sphere on each end. It was labeled "gravitational wave generator."

To this day, I'm not sure if it was a joke or a real device used for tuning LIGO... still a funny thing to find laying around :)

Re:Gravity Wave Generator - At Caltech (1)

budgenator (254554) | more than 8 years ago | (#15606754)

I'm sure that any gravity waves it produce would be overwhelmed by the mechanical vibrations, intermitant air currents, and EMF noise it would make, short answer it must have been a joke.

Detector location (1)

SEWilco (27983) | more than 8 years ago | (#15607308)

The detector is in Germany, visible on Google Maps [google.com] photos. The beam arms are WNW of the arrow, along a trapezoid-shaped field with a power line tower (look for the shadow) in it. The beam arms form a 93 degree angle and resemble a road at the default zoom. The GEO 600 visitors page [uni-hannover.de] has a different photo.
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