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Where are the missing gravitational waves?
- fit2rule 11y agoMust .. resist .. urge .. to make .. Mom joke .. aarrgh!
- elorant 11y agoRelevant http://www.dailygalaxy.com/my_weblog/2015/09/-missing-gravitational-waves-in-the-fabric-of-the-universe-leads-to-black-hole-rethink.html http://www.dailygalaxy.com/my_weblog/2015/09/-missing-gravit...
- ibizaman 11y agoI like how they state clearly that the result they obtained, even though unexpected, does mean that there are things that we still do not know, not that all we know must be burned to the ground.
- snorrah 11y agoI also like how their possible suggestions for why theories might not be panning out points to not enough understanding about something. So now we have a new scientific understanding to pursue. And on the way to figuring out /that/ new thing, we'll probably run into even more questions that need answering! In some ways, this is exciting - deepening mysteries always provoking further study. But on the flip side, it also makes me ponder the thought that maybe we will never gain true knowledge of the universe. At least, probably not before a very long time passes.
- amelius 11y ago> But on the flip side, it also makes me ponder the thought that maybe we will never gain true knowledge of the universe. Therefore, we might need to address the problem from the other end. This requires a totally different mindset. See for example the work done here: [1], or see the video lectures starting here: [2] [1] http://www.liv.ac.uk/physical-sciences/events/fpl/ http://www.liv.ac.uk/physical-sciences/events/fpl/ [2] https://www.youtube.com/watch?v=W2XdhzCORbo https://www.youtube.com/watch?v=W2XdhzCORbo
- imglorp 11y agoIt's been 472 since humanity realized the Earth moves around a star, 328 years since we knew the equations of gravitation, only 100 since we learned about GR, and only 15 years since we were certain the universe is expanding. I think we might be excused to take a few more years to nail down the rest of gravitation. There's an embarrassment of riches of data; it just needs assembling into a picture.
- JackFr 11y agoAnd 412 since someone noticed "[T]here are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."
- stcredzero 11y agomaybe we will never gain true knowledge of the universe If you are equating true knowledge with perfect knowledge, this obviously should be considered a straw-man. There is no reason why the rules completely describing universe should have to fit in a human mind. Our brains were evolved to solve the specific context of our prehistoric survival.
- GnarfGnarf 11y agoIt goes deeper than that. I think the human mind is fundamentally incapable of understanding Nature and reality. We make clever models, increasingly sophisticated and successful at manipulating matter and energy within the limited realm of our perception. However, we will never truly grasp the outside World. Every discovery will open up another can of worms, in an endless chase for more refined models. Today it's Dark Energy and Dark Matter. Centuries from now our views will seem as naïve and simplistic as Phlogistics and 19th-century Ether. That's OK though, as long as we're having fun. And don't blow ourselves up. And love and laugh.
- eli_gottlieb 11y agoIf our models are of ever-increasing sophistication and empirical success, why don't they count as truly grasping the world?
- lbenes 11y agoI’ve always felt that theoretical physicists should give more thought to the implication that gravitational waves don’t exist. Just maybe it would require reworking relativity in a way that’s more compatible with quantum mechanics. Sadly, it seems that everyone seems to think the flaw is with the standard model not the other way around.
- biswaroop 11y agoA lack of gravitational waves would mean information can travel infinitely fast, a Lorentz violation. There's no evidence in QM (or anywhere, really) that this is true.
- Manishearth 11y agoWe usually build up our QM models assuming Lorentz invariance, so this is somewhat a self fulfilling prophecy.
- cdelsolar 11y agoBut why do they have to be "waves"?
- lurcio 11y agoI'd rather take evidence from observation than from QM: let theory burn, as the current paradigm surely will if science ever trumps politics and regains its senses.
- biswaroop 11y agoYou'd think a binary pulsar would be ideal for measuring gravitational waves: they're precise clocks swimming in rapidly changing gravitational fields. Interestingly, binary systems of pulsars are the only source of evidence for gravitational waves. Astronomers use the pulsar timing to detect the slowing of orbital motion due to gravitational wave emission. I wonder if it's possible to detect a 'local gravitational wave background' modulating the pulsar timing on top of the usual modulation from the slowing binary.
- raverbashing 11y ago> Astronomers use the pulsar timing to detect the slowing of orbital motion due to gravitational wave emission. Correct, at least that's the theory But that's not evidence of gravitational waves per se, rather an evidence that a spinning binary system will have a velocity decay (and gravitational waves fit the description of what might be happening) So maybe there's an issue with how we measure it, how it actually affects matter or "it's complicated"/"it doesn't exist"
- versteegen 11y agoBut the rate of orbital decay of pulsars in binary systems is very precisely matched by general relativity, which is going to be very hard to explain with a different cause. Given that GR has been verified so thoroughly, while on the other hand models of the gravitational background depend on so many assumptions and simulations and approximately measured empirical relationships about supermassive black hole (SMBH) sizes, occurrences, time for SMBH mergers, etc, as detailed in the article, clearly this is incredibly weak evidence that gravitational waves don't exist. But something is wrong somewhere.
- PaulHoule 11y agoMaybe they went the same place that the missing mass went.
- idlewords 11y agoI don't understand this sentence: "During this time, we have accounted for every single one of the neutron star’s 116 billion rotations" Isn't this pulsar just being watched by one radio telescope in Australia, which presumably can't point at it 24 hours a day?
- lisper 11y agoGood question. You don't need to directly observe every rotation in order to "account" for it. The drift rate for a pulsar is extremely low, so as long as you sync up often enough that the error is much smaller than one cycle you can be confident that you've counted every one even though you haven't directly measured them all.
- arethuza 11y agoIf it's a circumpolar star then it won't set - e.g. Polaris doesn't set here in the UK.
- hugh4 11y agoTrue but I think lisper's answer is correct since I'm sure they haven't kept the Parkes radio telescope trained on one target for eleven years.
- ars 11y agoGravitational waves contain (are?) energy https://en.wikipedia.org/wiki/Sticky_bead_argument https://en.wikipedia.org/wiki/Sticky_bead_argument Since they contain energy, they in turn have mass, and a gravitational field of their own. Which is quite an interesting implication, because since they travel at the speed of light, they can't slow down when interacting with mass, instead they must do some sort of "blue shift". It also means that when the waves are bent by traveling near a large mass, those waves emit daughter waves of their own. And one part of the gravitational wave is attracted by another part of it. I suspect that a combination of those processes adds so much noise that there is no detectable signal left.
- drjesusphd 11y ago> Since they contain energy, they in turn have mass, That is not true... > and a gravitational field of their own. ... although this is. It's energy that creates a gravitational field, of which mass is a (usually dominant) subset. It does not mean anything with energy has mass. See: light. Edit: also, the basic theory of gravitional waves is "linearized", which means that this kind of self-interaction is weak. That doesn't mean it doesn't happen, but it wouldn't resemble radiation if the effect is strong.
- ars 11y ago> It does not mean anything with energy has mass We are using different definitions of mass. I'm calling invariant energy mass, you are calling rest energy mass. > but it wouldn't resemble radiation if the effect is strong The wave does have a frequency though, which must blueshift as it interacts with matter.
- tfgg 11y ago> We are using different definitions of mass. I'm calling invariant energy mass, you are calling rest energy mass. Modern physics only refers to rest mass [1] as 'mass', otherwise people tend to get confused about how 'relativistic mass' (γm) affects gravity. [1] E/c^2 in a centre of momentum frame, which doesn't exist for an object travelling at c
- wcoenen 11y agoAdvanced LIGO has come online sometime in the last 10 days[1] and there is a rumour that it has already detected a gravitational wave[2]. [1] http://news.mit.edu/2015/advanced-ligo-begins-operations-0917 http://news.mit.edu/2015/advanced-ligo-begins-operations-091... [2] https://twitter.com/LKrauss1/status/647510799678750720 https://twitter.com/LKrauss1/status/647510799678750720
- fugyk 11y agoThat will be huge if true. Gravity wave will tell us many things about the very early universe(first few 100,1000s of years!), for which we have very little data now. Its an amazing achievement for LIGO just after 10 days of its start.
- cabinpark 11y agoI work in numerical relativity and our group produces many, many gravitational waveforms. I even visited LIGO this past summer. If Lawrence Krauss isn't bullshitting (and I have no reason to doubt he would be) then this is absolutely huge news. Nobel Prize worthy discovery no question.