Lab Tuned to Gravity's 'Ripples' 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. "
negative outcomes? (Score:3, Interesting)
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? (Score:3, Insightful)
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? (Score:2)
Think bigger: Anti-Gravity-Sex !
Re:negative outcomes? (Score:1)
Re:negative outcomes? (Score:2)
Re:negative outcomes? (Score:1)
Re:negative outcomes? (Score:2)
Re:negative outcomes? (Score:5, Insightful)
let me be more precise (Score:2)
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 (Score:4, Informative)
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 (Score:2)
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
Re:let me be more precise (Score:3, Insightful)
Re:let me be more precise (Score:3, Interesting)
To the degree that the spin-off applications are valuable, the spi
Re:let me be more precise (Score:2)
Experimentation is as much about what we don't expect as it is about finding predicted results. The discovery of penicillin is the obvious example of this. In the long run, selecting scientific experiments for economic value over scientific value would destroy the pursuit of science. Investing only in "safe" and "predictable" outcomes means only reaping small, predictable returns.
Sounds like g
Re:let me be more precise (Score:2)
Hmmn. I take your point. I really do. But I have to stress my earlier point - the spin-offs will never be started without
Re:let me be more precise (Score:2)
Yes, and I think that's a very narrow view. Large scale experiments are almost the exclusive domain of a small subset of experimental physicists (and, very recently, a few biologists). Prior to the bomb, even most physics experiments were bench-top, but the cold war gave a small subset of physicists a lot of power to obtain large amounts of funding. Other disciplines really have not had the luxury of demanding to do a huge, expensive experiment
Re:let me be more precise (Score:2)
Re:let me be more precise (Score:2)
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 technol
Re:negative outcomes? (Score:2)
Re:negative outcomes? (Score:2)
Re:negative outcomes? (Score:2)
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? (Score:5, Insightful)
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.
wrong (Score:2)
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? (Score:2)
Re:negative outcomes? (Score:2)
Re:negative outcomes? (Score:3, Insightful)
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? (Score:2)
Re:negative outcomes? (Score:2)
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? (Score:2)
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 eno
Re:negative outcomes? (Score:2, Interesting)
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 cas
Re:negative outcomes? (Score:2)
That's a common cop-out. In fact, there is only a limited amount of funding that can be "created"; if this funding wasn't "created" for those experiments, it could be "created" for other experiments by researchers in
Re:negative outcomes? (Score:2, Interesting)
It's not a cop-out. Look at the history. For the very large experiments, it's almost never the case that the funding committee goes "Well, we could fund this big experiment, or we could give everyone else in the field the equivalent amount of money instead". Usually, if they don'
Re:negative outcomes? (Score:2)
Great! So, that was what my original question was about. However, it's not sufficient just to point at "a small moon" "carpeted in theories", you also need to explain how the different theories actually differ, whether they make different predictions for this experiment, and what those predictions are. Unfortun
Re:negative outcomes? (Score:2)
Yes, and I have already told you that it must be part of the description of such an experiment, both in the grant application and in any paper describing results; it is not sufficient for the information to exist somewhere in the literature.
That you are ignorant of this work is not a testament to the incompetence of LIGO physicists, it simply speaks to your own incompetence.
Your assumption about what I kn
Re:negative outcomes? (Score:1, Insightful)
Re:negative outcomes? (Score:1)
Re:negative outcomes? (Score:2)
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? (Score:5, Interesting)
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? (Score:1)
Isn't this how religions get started?
Re:negative outcomes? (Score:2)
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? (Score:2)
"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 - wh
Re:negative outcomes? (Score:2)
But the article says something different: "
Re:negative outcomes? (Score:5, Interesting)
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? (Score:3, Interesting)
Re:negative outcomes? (Score:3, Informative)
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' experien
Re:negative outcomes? (Score:2)
If we had no creativity then we wouldn't have this test in the first place.
Re:negative outcomes? (Score:2, Interesting)
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
Re:negative outcomes? (Score:1, Insightful)
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 sen
Re:negative outcomes? (Score:1)
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 genera
Re:negative outcomes? (Score:1)
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,
Re:negative outcomes? (Score:3, Insightful)
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 anot
Re:negative outcomes? (Score:3, Informative)
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, th
Re:negative outcomes? (Score:3, Funny)
Intelligent falling [theonion.com]. After all, gravity is just a theory.
Re:negative outcomes? (Score:2)
Re:negative outcomes? (Score:2)
It's important to have alternative hypotheses...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.
Huh? I simply don't understand this idea at all. Historically science hasn't come up with alternate explanations before they do an experiment with an expected result. Michelson-Morley fully expected to confirm the existence of the aether wind, and had no a
Re:negative outcomes? (Score:2)
You should read up on the history of physics. Pay particular attention to the phlogiston, Antoine Lavoisier and the solar neutrino problem; all three are cases where it wasn't until we had disproving experimental data that we had enough information to even begin to formulate alternate theories.
Moment of Creation (Score:3, Funny)
Re:Moment of Creation (Score:2)
Mmmmmm.. Ripples..... (Score:5, Funny)
Eddies in the Space/Time Continuum (Score:5, Funny)
Re:Eddies in the Space/Time Continuum (Score:2)
Re:Eddies in the Space/Time Continuum (Score:2)
Will they measure the speed of gravity as well? (Score:3, Insightful)
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 (Score:3, Funny)
Steve
Re:Will they measure the speed of gravity as well? (Score:5, Informative)
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? (Score:1)
>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
Re:Will they measure the speed of gravity as well? (Score:2)
As has already been pointed out, quantum mechanics does not allow particles (or information) to travel faster than light. Essentially, if a particle is localized on one side of a barrier, it takes time for it to tunnel through to the other side (this is the time for the wavefunction to spread in non-relativistic QM, or the time for disturbances in the quantum field to propagate in quantum field theory) so that if you measure again before the particle could have gotten through the barrier at the speed of l
Re:Will they measure the speed of gravity as well? (Score:2)
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? (Score:4, Funny)
Re:Will they measure the speed of gravity as well? (Score:2)
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 prob
Re:Will they measure the speed of gravity as well? (Score:2)
Yes. It also violates special relativity and the laws of cause and effect.
Whereas I'm certainly not defending the grandparent post, as the poster was a huge douchebag, I should point out that in fact there are several things whose effects can cross a distance in a timeframe shorter than that which light would also take. Given that we're not entirely sure of the nature of gravity, we don't actually know tha
Re:Will they measure the speed of gravity as well? (Score:2)
Re:Will they measure the speed of gravity as well? (Score:2)
Re:Will they measure the speed of gravity as well? (Score:2)
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? (Score:2)
Re:Will they measure the speed of gravity as well? (Score:4, Funny)
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
Love the idea though rofl
Re:Will they measure the speed of gravity as well? (Score:2)
Re:Will they measure the speed of gravity as well? (Score:2)
Re:Will they measure the speed of gravity as well? (Score:2)
If the speed of gravity is greater than the speed of light, does that violate the general relativity?
No. But still, it isn't faster than light. Also, there are several things which are faster than light without violatin
Wow, I need to get laid (Score:2, Funny)
You can participate (Score:5, Informative)
This experiment uses distributed computing to process their results,
and you can participate.
uh.. about creation... (Score:1)
It's the moment before that I want to know about... Oh, wait...
what if it cancels itself out? (Score:1)
Question for a Physics Buff (Score:1)
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 pho
Re:Question for a Physics Buff (Score:1, Informative)
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?
Gravity Wave Generator - At Caltech (Score:2)
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 layi
Re:Gravity Wave Generator - At Caltech (Score:2)
Re:Gravity Wave Generator - At Caltech (Score:2)
I'm not so sure... all of that stuff dies out with at least inverse-distance-squared (faster for higher order moments) on its own, however EMF and mechanical vibrations are dampened considerably by ordinary matter, whereas gravity waves are affected much less... I would imagine that a device like this would be used se
Re:Gravity Wave Generator - At Caltech (Score:2)
Re:Gravity Wave Generator - At Caltech (Score:2)
Re:Gravity Wave Generator - At Caltech (Score:2)
Re:Gravity Wave Generator - At Caltech (Score:2)
The reason it's funny is that anyone who has sense knows that that kind of thing is way, way outside of our technology, and that it's only such an object on a technicality. To use your own example, if someone put a sign on a brick that said "sound generator," that would be essentially tr
Can someone explain Feynman's thought experiment ? (Score:2)
When asked if gravity waves [wikipedia.org] could transmit energy, RPF in 1957 had the following argument
Feynman's argument
Later in the Chapel Hill conference, Feynman -- who had insisted on registering under a pseudonym to express his disdain for the contemporary state of gravitation physics -- used Pirani's description to point out that a passing gravitational wave should in principle cause a bead on a stick (not oriented parallel to the direction of propagation of the wave) to slide back and forth, thus heating
Re:Can someone explain Feynman's thought experimen (Score:2)
Re:Can someone explain Feynman's thought experimen (Score:2)
At last :-) (Score:2)
Re:ripples in fabric of space-time? (Score:3, Funny)
Re:ripples in fabric of space-time? (Score:5, Interesting)
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? (Score:2)
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? (Score:2)
The issue is one of context. We have a whole bunch of data that we're not entirely sure how to interpret, and although we have a lot of very convincing extrapolations, we really can't work with them until we know some of the foundational material is correct. There are dozens of examples o