Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Physicists Detect Gravitational Waves, Proving Einstein Right

nytimes.com

Post reply on HN
Print view View original

471–480 of 502 posts

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#471

Post by JabavuAdams »

selimthegrim wrote: post #266
JabavuAdams wrote: post #255

Where can I find out more about how thermal effects in the LIGO optics are controlled for? Basically, I want to understand how it's possible to measure a distance change on the femtometer scale.

You probably want to read about their active isolation measures. Then you should find anything by Vladimir Braginsky you can get your hands on. This is a good start: http://www.amazon.com/Quantum-Measurement-Vladimir-B-Bragins...

More accessible / concise info on the vibration isolation, here: https://news.ycombinator.com/item?id=11084282

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#472

Post by rotorblade »

Manishearth wrote: post #467
cyphar wrote: post #394

Earlier quoted context omitted.

Only electrons get mass from the Higgs mechanism. Most of your mass comes from your protons and neutrons (or rather the energy "stored" in the bonds between the quarks that make them up).

You're talking about binding energy, and that's not where the majority of mass comes from. All massive particles get their mass from the Higgs field.

All _fundamental_ particles gets their mass from the Higgs (up to some issues with the neutrinos). Composite particles, say the Proton, is a strongly coupled system (that is, can not be described by perturbation theory) and it does not have the mass being the sum of its constituents (not even most of it). Hence, it is not known what gives most of the mass of particles such as the Proton.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#473

Post by Ensorceled »

JabavuAdams wrote: post #469
Ensorceled wrote: post #374

Earlier quoted context omitted.

Google "sun percentage mass solar system" and the highlighted answer is "By far most of the solar system's mass is in the Sun itself: somewhere between 99.8 and 99.9 percent." Please don't just disagree when you don't know what you are talking about.

I think you've misinterpreted my post. The "No" was in response to this: > 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? No, that isn't enough mass to explain dark matter, since it's only 0.1% to 0.2% of the mass of the solar system. The text I quoted wa…

Ok, that's just a really confusing way of communicating, nobody is going to puzzle that out when the obvious way of looking at your response is disagreement with the grandparent.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#474

Post by aws_ls »

jshelly wrote: post #44

Does anyone else get a bit depressed when you consider how insignificant we are?

I do. People compare crossing the oceans with space travel. In our present form (on evolutionary scale) we are less than equipped for that.

Also I wonder, in this form as humans, can anyone really comprehend what this all means, beyond the Math and experimental confirmations?

What if we are living in a simulation, and just being played?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#475

Post by terryf »

evanpw wrote: post #280
theophrastus wrote: post #260

Earlier quoted context omitted.

Here's my re-statement of this confusion, isn't everything we can experience embedded in time-space, including the LIGO experiment itself? So how is there any relative shift allowed to be detected when everything we know is fundamentally intrinsic to time-space? That is, I too would appreciate having this mis-conceptualizing, of mine, cleared away.

Another re-phrase: how can we detect that space has stretched out if all of our rulers also get stretched by exactly the same amount? The answer is that we have a ruler that doesn't get stretched in this way: light. The speed of light is a constant dictated by the laws of physics; stretching out our flashlight to twice its normal size wouldn't make the light it emits go twice as fast. So if you just measure the time…

Thanks for the nice explanation! But another question: since the expansion rate of the universe has been different at different times, does this mean that the measured speed of light would be different at different times as well?

Because if the ruler you are using to measure is expanding at rate x, the measured speed of light would be different than when the ruler is expanding at rate y?

So, during the deflationary period of the universe, the speed of light would be significantly smaller, correct? In fact, would it be "negative" due to the universe expanding faster than light?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#476

Post by Manishearth »

rotorblade wrote: post #472
Manishearth wrote: post #467

Earlier quoted context omitted.

You're talking about binding energy, and that's not where the majority of mass comes from. All massive particles get their mass from the Higgs field.

All _fundamental_ particles gets their mass from the Higgs (up to some issues with the neutrinos). Composite particles, say the Proton, is a strongly coupled system (that is, can not be described by perturbation theory) and it does not have the mass being the sum of its constituents (not even most of it). Hence, it is not known what gives most of the mass of particles such as the Proton.

Er, sorry, implicitly was talking about fundamental particles.

IIRC we do know where protons get their mass. The internal color field has some energy, thus some mass, which comes from that field interacting with Higgs.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#477

Post by astrodust »

mattmanser wrote: post #386
mikeash wrote: post #363

Earlier quoted context omitted.

I'm sure He either said "let there be light" or "gee, that's funny...."

I'd prefer either "what does this button do?" or "shit, don't press that!".

"I clicked print and nothing happened!"

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#478

Post by semi-extrinsic »

mahranch wrote: post #402
semi-extrinsic wrote: post #307

Earlier quoted context omitted.

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.

> no multiverse theory has yet been put forth that is experimentally testable Just to be clear here; that's because there is no theory for a multiverse. Not yet, anyways. Nobody has put one forth yet. When you hear "multiverse" come out of physicist's mouth, it's because it's a concept indirectly related to other theories. The current popular theory which involves a multiverse is string theory. When string theorists…

These are very good points. I do agree that it's possible someone could come up with a testable multiverse-type theory.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#479

Post by SaberTail »

thfuran wrote: post #249
SaberTail wrote: post #212

Earlier quoted context omitted.

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 gra…

How does the mediating particle being affected by the force translate to a shorter range?

There are two aspects to it. And I'll be very hand-wavey because QCD is not my field.

Suppose you have two quarks and you start to pull them apart. The gluons that transmit the force between the two quarks tend to "bunch" together because they have their own charge. You can think of it roughly like a rope of gluons trying to pull the quarks back together.

If you keep pulling on the quarks, you might expect the gluons to eventually "break". But this doesn't happen, because the gluons act on each other. If there were ever a break, more gluons would join in, tugging the break back together. Eventually, you end up with so much energy density in all these gluons that they start forming new quarks and other particles. These new particles will bind with your quarks and each other to form color-neutral particles.

So I spoke a little imprecisely. Gluons, being massless, have infinite range. But you won't ever see the strong force acting over any large distance because anytime you try to get color-charged particles far enough apart, you'll end up making more particles.

Wikipedia has a brief write-up that provides an illustration. https://en.wikipedia.org/wiki/Color_confinement

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#480

Post by zardo »

losteric wrote: post #384
Crito wrote: post #372

Earlier quoted context omitted.

Could such a device be used to increase the reaction mass of your fuel when it exits your engine? A sort of way to cheat F=MA by artificially boosting M, but only after you are in orbit?

No, you're confusing mass and weight. Mass is the amount of matter in a thing. Weight measures gravity's pull on the thing. This theoretical device could make things weight more than with just Earth's gravity... but it wouldn't help your spaceship. Your engine is still pushing out the same amount of matter, so thrust remains unchanged.

You could definitely boost an orbit by increasing the force of gravity while approaching periapsis.
Post reply on HN