Physicists Detect Gravitational Waves, Proving Einstein Right • Hacker News Board

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#301

Post by tfgg » Thu, Feb 11, 2016, 9:55 PM UTC

sandworm101 wrote: post #272

contravariant wrote: post #210

Earlier quoted context omitted.

Force carrying particles in general don't have mass. Except that some of them seem to do, which was rather puzzling for some time, but was solved using the Higgs mechanism. I can't think of an obvious reason the Higgs mechanism wouldn't work for gravitons, but I could be mistaken, it's not exactly the most intuitive area of physics. Also, keep in mind that the strong force transmits the force between colour charges w…

If the massive gravitron was leaving a black hole it would be slowed by the black hole's gravity. (1) We should see this as some inconsistency in how gravity scales with the mass of a black hole. The larger ones would have proportionately greater 'drag' on leaving gravitrons, pulling more in. (2) If they are massive, and therefore subject to slowing, shouldn't gravity waves leaving a black hole be subject to some sor…

(None of my points below say the graviton is massless, just that it's not crazy. As another post says, this new observation probably confines the graviton mass to be less than 10^-55 grams)

> If the massive gravitron was leaving a black hole it would be slowed by the black hole's gravity.

A graviton wouldn't be able to escape a black hole. A photon can't, and it's massless. The gravity of a black hole is actually a self-sustaining effect of the curvature of the spacetime around the black hole.

> (1) We should see this as some inconsistency in how gravity scales with the mass of a black hole. The larger ones would have proportionately greater 'drag' on leaving gravitrons.

We don't know details of the gravitational field around black holes and the mass that created it, because none have been observed close up. To an extent, the mass of a black hole is defined by its gravity.

> (2) If they are massive, and therefore subject to slowing, shouldn't gravity waves leaving a black hole be subject to some sort of doppler effect? Should we be looking for red/blueshifts in these waves?

Again, photons are massless and subject to the doppler effect. Gravitons, massless or not, will be too.

> (3) If gravitrons have mass and are subject to gravity, what brings that gravity? What sub-gravitron particle regulates gravity going in/to/out of the gravitron? This would require a new set of particles be created by non-gravitron massive objects (ie black holes) alongside the gravitrons. Like I said, too strange to exist.

Force carying particles can interact with themselves, c.f. gluons in QCD. In fact, GR is a non-linear theory so there will be non-linear interactions (as far as you can describe them in the weak limit).

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#302

Post by dheera » Thu, Feb 11, 2016, 9:56 PM UTC

ernesto95 wrote: post #195

I generally dislike idolatry and pinning mayor scientific advancement on one single person, but honestly, Einstein really was something else.

In all honesty I do think Einstein is getting too much credit today. I'd paste the list of co-authors here to congratulate them but HN doesn't allow comments that large. The list is available here for reference, and I think every one of them deserves credit for this.

  http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102

On another note, I feel like the importance of this finding is less in proving Einstein's theory; having taken a formal relativity class and an degree in Physics, I think GR itself is an astounding mathematical framework for describing spacetime, to which Einstein deserves credit, but the existence of gravitational waves is completely natural consequence of the equations within. It's not very different from the existence of light being a natural consequence of Maxwell's equations.

I'd say the true importance of this discovery is in successfully creating an experimental apparatus to detect what was previously almost universally agreed to probably exist but thought to be nearly impossible to detect. What's truly exciting isn't proving Einstein right, but the possibilities of what we'll be able to to detect with this apparatus in the future. So it's the team that built the apparatus which truly deserves the credit today.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#303

Post by bobinator606 » Thu, Feb 11, 2016, 9:56 PM UTC

spullara wrote: post #78

As with most physics experiments for the last 40 years, nothing new was discovered that we didn’t already predict. Confirming something widely believed to be true isn't nearly as valuable as finding out we don't understand something. This is actually one of the reasons I dropped out of my physics phd program.

Then you should have concentrated on theoretical physics instead of experimental?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#304

Post by [deleted] » Thu, Feb 11, 2016, 9:57 PM UTC

dragonwriter wrote: post #237

brudgers wrote: post #183

Earlier quoted context omitted.

Under the theory of science as the study of what is falsifiable, there's nothing here to falsify because there is no way to disprove that a conjectured but unobserved collision of two massive bodies was something else or didn't occur. Which is to say that it is impossible to falsify that a conjecture is a conjecture. That there is not a geophysical theory, doesn't have a bearing on the correctness of the gravitationa…

> Under the theory of science as the study of what is falsifiable, there's nothing here to falsify because there is no way to disprove that a conjectured but unobserved collision of two massive bodies was something else or didn't occur. Yes, there is: if the predicted kind of observations did not occur, it would imply one of two things: (1) the model of gravity waves and their generation and propagation on which the…

[deleted]

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#305

Post by BurningFrog » Thu, Feb 11, 2016, 9:57 PM UTC

daveguy wrote: post #163

snowwrestler wrote: post #70

Earlier quoted context omitted.

Well we've accounted for about 5% of the universe--the stuff we know about. Dark matter (about 25%) seems to only interact gravitationally, which means that we've just, today, proven that we have an instrument that could possibly observe it directly. To date, all our evidence for dark matter is indirect--observing the otherwise unexplained behavior of normal matter. Today is the gravitational equivalent to Galileo po…

How do we know dark matter is some mysterious form of matter and not just small distributed particles (gas or solid) that are beyond our ability to detect? Do we have proof of a specific, exotic, non-atomic matter?

"Dark Matter" is an unfortunate name, since it sounds like regular matter that is not adequately lit.

In reality, it's something we have no idea what it is, except that it's not visible and a big source of gravity.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#306

Post by kordless » Thu, Feb 11, 2016, 10:01 PM UTC

contravariant wrote: post #210

sandworm101 wrote: post #181

Earlier quoted context omitted.

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.

Force carrying particles in general don't have mass. Except that some of them seem to do, which was rather puzzling for some time, but was solved using the Higgs mechanism. I can't think of an obvious reason the Higgs mechanism wouldn't work for gravitons, but I could be mistaken, it's not exactly the most intuitive area of physics. Also, keep in mind that the strong force transmits the force between colour charges w…

I'm going with the theory that black holes ARE gravitons themselves.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#307

Post by semi-extrinsic » Thu, Feb 11, 2016, 10:05 PM UTC

zoke wrote: post #222

antognini wrote: post #10

Earlier quoted context omitted.

The predictions for the LIGO detection rate are very poor. They're based on a sample of just a handful of binary pulsars observed in our Galaxy, which would produce NS-NS mergers. The BH-BH merger rate is almost totally unconstrained, although it is generally thought to be less than the NS-NS merger rate. So the fact that a BH-BH merger was the first detection, and the fact that it was detected so soon after the sens…

I recall reading some years ago that gravitational wave would be used to prove multiverse theory. How would that scale compared to bh-bh or ns-ns mergers? Also, have read today that this discovery backs inflationary theory, how so? It seems highly unlikely that they could say a specific bh-bh merger was the cause. It seems implied they are triangulating the source, with two detectors?

AFAIK no multiverse theory has yet been put forth that is experimentally testable (even in theory given infinite time, energy etc.) So it's not a proper (falsifiable) scientific theory at present, merely a (in my opinion wild) conjecture.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#308

Post by kordless » Thu, Feb 11, 2016, 10:06 PM UTC

bbcbasic wrote: post #284

Panoramix wrote: post #267

Earlier quoted context omitted.

They also injected fake signals into the detector now and then, partly to keep the analysts on their toes. http://www.ligo.org/news/blind-injection.php

I don't think they are expected to tell its fake though? It's hard to do a double blind experiment without a "placebo universe".

That's a rather loaded philosophical question you are asking there - assuming you are serious about the double blind experiment.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#309

Post by ajkjk » Thu, Feb 11, 2016, 10:11 PM UTC

stevebmark wrote: post #289

vickychijwani wrote: post #264

Earlier quoted context omitted.

Check the comic posted by AdrianN, it explains what you're missing. Basically light takes longer to travel stretched space (but matter does not, as you correctly said).

I see. If that's true, then light travels through a higher dimension, and this is definitive proof of at least a fourth spatial dimension. Otherwise there would be nothing for the 3d space to ripple through, or for light to travel through. I'm surprised I haven't heard that light travels independent of 3d space compression before. That would also imply that if you enter a black hole with your feet at the bottom, you…

I don't really know how you jumped to 'higher dimensions' from that.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#310

Post by mehwoot » Thu, Feb 11, 2016, 10:12 PM UTC

drx wrote: post #252

tossaway1 wrote: post #226

Earlier quoted context omitted.

If these waves travel at the speed of light shouldn't the distance and time match up...?

This would be true in a static universe, but, during the 1.2 billion years the waves have been traveling, the universe was experiencing accelerating expansion. For example, the edge of the observable universe is about 46.5 lightyears away, while the universe is thought to be 13.8 billion years. https://en.wikipedia.org/wiki/Observable_universe#Misconcept...

is about 46.5 lightyears away

I assume you mean 46.5 billion?