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Physicists Detect Gravitational Waves, Proving Einstein Right

nytimes.com

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Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#211

Post by brudgers »

gaur wrote: post #113
brudgers wrote: post #109

I am a bit skeptical of the conclusion given the methods. Here, there's no observable phenomena independent of the test apparatus that corresponds to the proposed cause. The conclusion is circular. 1. Theory predicts gravitational waves when massive objects collide and that the gravitational waves would have an effect that could be measured by the experimental instruments. 2. The experimental instruments measure some…

> That's not to say that what the phenomena measured -- the earth resonating That's not what the detector measures. RTFA.

I read the article. I am in the habit of calling periodic changes in dimension "resonance." I consider it rather consistent with the use of "wave" in the discussion and hence a handy way of describing what the instruments measured rather than what the theory suggests as the first cause.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#212

Post by SaberTail »

sandworm101 wrote: post #181
ScottBurson wrote: post #176

This made me wonder how far we are from being able to create and detect gravitons. The Wikipedia page on gravitons [0] addresses this question: Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is impossible with any physically reasonable detector. The reason is the extremely low cross section for the interaction of gravitons with matter. For example, a detector with the mas…

If gravitons have mass, then the universe is too strange to exist. Gravity is an interaction that defines the presence of matter (see dark matter). For the object that transmits that force between masses to itself have mass ... how can a black hole then project gravity? Imho whatever is carrying gravity between masses cannot itself have a mass.

What do you think of the strong nuclear force? Gluons are the force carriers between color-charged particles. And gluons themselves have a color charge. So gluons transmit force between each other. Does that mean the universe is already too strange to exist?

By the way, this is why the strong nuclear force has such a short range. Gravity has infinite range as far as we can tell, so that makes it unlikely that the graviton, if it exists, has mass.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#213

Post by jdmichal »

JoeAltmaier wrote: post #186
snowwrestler wrote: post #180

Earlier quoted context omitted.

Scientists are pretty sure that dark matter is not just regular gas and dust because the amount required to create the gravity we see, would be visible. It would block or reflect a lot of the nearby starlight. Just on the back of an envelope: If we assume the percentages in my post above apply to an individual galaxy, then there has to be 5x as much dark matter mass as lit mass. There's no way you could have 5x as mu…

That always confused me. We have an Oort cloud, whose members we cannot resolve very well/at all. Why do we assume only our star has such a thing? If all stars did, that isn't enough mass to explain dark matter?

The total mass of the Oort cloud is guessed at (3×10^25 kg), or about five Earth masses. With dark matter, we are talking about roughly 5.6x the amount of the total solar system mass. The Oort could would need to be about 371,691x more massive than it is.

https://www.wolframalpha.com/input/?i=mass+of+the+solar+syst...

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#215

Post by nanofortnight »

wildmusings wrote: post #114
soneca wrote: post #108

Honest question: there is any example of Einstein being proved wrong ? Was he indeed always right on his theories for phenomenons before they could be proved by experiments; or is that the case that we only hear about when he is proved right?

He was a proponent of hidden variable theory, which tried to reconcile quantum mechanics with determinism, famously saying "God does not play dice". People often say that hidden variable theories were proven impossible, and thus Einstein was proven wrong. That's not quite true, and only local hidden variables have been ruled out.

Non-local hidden variable theories are viable, however, such as de Broglie–Bohm.

I don't think Eistein would've liked those much either due to 'spooky action at a distance'.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#216

Post by gaur »

brudgers wrote: post #211
gaur wrote: post #113

Earlier quoted context omitted.

> That's not to say that what the phenomena measured -- the earth resonating That's not what the detector measures. RTFA.

I read the article. I am in the habit of calling periodic changes in dimension "resonance." I consider it rather consistent with the use of "wave" in the discussion and hence a handy way of describing what the instruments measured rather than what the theory suggests as the first cause.

The instruments are intentionally constructed to be as insensitive as possible to earth motion.

Implicit in the detection claim is that the signal does not originate from earth motion.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#217

Post by InclinedPlane »

scrumper wrote: post #47

From the abstract of the paper, energy equivalent to three solar masses were radiated away in gravitational waves. That's a simply incredible amount! Possibly stupid question: Given how far away it was, and that the inverse square law applies, would the effect of these waves be visible on the human scale if we were closer? We can see the effects of the compression of spacetime with LIGO after all, so presumably we co…

Yup. Possibly one of the most energetic events in the Universe. Fascinating in many ways when you think about it. That mass was once matter, and somehow it got converted into gravitons.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#218

Post by [deleted] »

JoeAltmaier wrote: post #186
snowwrestler wrote: post #180

Earlier quoted context omitted.

Scientists are pretty sure that dark matter is not just regular gas and dust because the amount required to create the gravity we see, would be visible. It would block or reflect a lot of the nearby starlight. Just on the back of an envelope: If we assume the percentages in my post above apply to an individual galaxy, then there has to be 5x as much dark matter mass as lit mass. There's no way you could have 5x as mu…

That always confused me. We have an Oort cloud, whose members we cannot resolve very well/at all. Why do we assume only our star has such a thing? If all stars did, that isn't enough mass to explain dark matter?

[deleted]

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#219

Post by stevebmark »

yosyp wrote: post #193
stevebmark wrote: post #174

How do the detectors work? In my mind they don't make physical sense. They're saying the distance between the mirrors changes, but I don't understand how that's possible in this context. Let's say a gravitational wave compresses space. To someone inside that compressed space, there should be no noticeable difference. Light will still flow the same way through the compressed space at the same speed relative to the com…

I think the crucial detail you are missing from the article is this: "According to the equations physicists have settled on, gravitational waves would compress space in one direction and stretch it in another as they traveled outward." LIGO is two sets of 2 L-shaped antennas spread far apart on the globe, so that we can compare the compression of space in orthogonal directions and measure the very short delay between…

I still don't understand. It doesn't matter where the compression happens, because it should be undetectable to any light/matter that's fundamentally a part of that space? If one of the arms gets compressed - the matter will be compressed too, so light still has the same density and amount of space to travel through?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#220

Post by brudgers »

corndoge wrote: post #119
brudgers wrote: post #109

I am a bit skeptical of the conclusion given the methods. Here, there's no observable phenomena independent of the test apparatus that corresponds to the proposed cause. The conclusion is circular. 1. Theory predicts gravitational waves when massive objects collide and that the gravitational waves would have an effect that could be measured by the experimental instruments. 2. The experimental instruments measure some…

http://physics.aps.org/assets/0e3ca952-a3d3-49f2-bbc2-259c0a... Lower two graphs are predicted waveform in event of binary system coalescence. Upper waveform left and right are observed events at each LIGO facility. Consider furthermore that the event was observed at each facility with the appropriate lightspeed time offset, and that the wave directionality of the event was lateral and not radial from the center of t…

It's not a gaping logical fallacy. It's human nature to tell interesting stories. Black holes colliding is sexy. "We measured a 10^-18 variation in the diameter of the Earth and we are uncertain regarding its cause" is not sexy.

As Jack Friday used to say, "Just the facts, mam."

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