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

81–90 of 502 posts

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#81

Post by gsibble »

snowwrestler wrote: post #70
pavpanchekha wrote: post #2

I remember learning about the LIGO experiment back when it was being built, a decade ago, and at the time it seemed so amazing: a giant tube of vacuum, sealed underground and so sensitive that it could detect animals walking nearby, listening to the moving and twisting of space itself… I guess we're finally seeing that with immense human ingenuity and the most careful of engineering, the universe will offer its secre…

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…

Completely agree. We have a long way to go.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#82

Post by QuadrupleA »

One thing I don't quite understand - how can the "chirp" from LIGO be unambiguously categorized as extraterrestrial in origin? The waveform shown onscreen in the NYtimes video looks like an extremely noisy signal - not sure if that's the actual sampled data or just an artistic rendition. Couldn't there be a variety of physical disturbances that explain a sine-tone sweep like that, given how sensitive the instrument is to physical vibrations?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#83

Post by bzbarsky »

davrosthedalek wrote: post #40
kordless wrote: post #21

Earlier quoted context omitted.

Think of waves in a pond when you drop a rock in. The energy spreads out as it travels into the farthest reaches of the pond.

Only that in space, it drops even faster: The wavefront carries the same energy, but spread out over ever increasing length/area. For gravitational waves (or radio waves) they form spheres, not circles, and the surface size scales with r^2, not r. (Also water waves are /complicated/)

Right, but LIGO detects wave amplitude, not wave energy, which goes down as 1/r.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#85

Post by cft »

QuadrupleA wrote: post #82

One thing I don't quite understand - how can the "chirp" from LIGO be unambiguously categorized as extraterrestrial in origin? The waveform shown onscreen in the NYtimes video looks like an extremely noisy signal - not sure if that's the actual sampled data or just an artistic rendition. Couldn't there be a variety of physical disturbances that explain a sine-tone sweep like that, given how sensitive the instrument i…

There are two independent sites, 2000 miles apart. Additionally, each site has two perpendicular experiments: one shows contraction when the perpendicular one shows expansion. Orientations at both sites are aligned I presume.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#86

Post by pif »

ericjang wrote: post #71

The mechanical and software engineering underlying these research endeavors is breathtaking. The laser apparatus, LISA pathfinder, ELISA - how on earth do they calibrate/debug/test such complex systems? ... and I shudder to think that more often than not, anything I code in C/C++ will segfault on first run.

Don't worry, their code segfaulted umpteen times, too :-)

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#87

Post by j1vms »

oldmanjay wrote: post #46
shmerl wrote: post #37

Earlier quoted context omitted.

> No one would have looked at the first computer and envisioned an iPhone. Not really. Portable computers were envisioned quite a long time ago.

Not before they were solid state. Computers had their own buildings and relied on glass tubes for operation. Screens weren't on the radar. Operators were highly educated. But technology did bring us to a point where the vision became more focused, and led to what we have today. There are many possible paths to rebutting my statement, which to be clear is idle morning musing, but your objection doesn't hold water.

I agree that you do make a point. There is really no way for us to know what is to come. Sometimes we think we are looking at a square, but it really is a cube and we are just unable to look beyond are current perspective for whatever reason.

I would say one obstacle that stands in the way of "spying" on objects moving on the Earth's surface is that the gravitational wave energy emitted by accelerating objects on Earth would be "too small" for current detectors. Not to mention that there would be the issue of how to filter gravitational wave noise, and/or isolate frequencies. However, if it possible to build an amplifier or filter to resolve these issues, that remains to be seen - or maybe somebody else could chime in.

edit: typos, clarity

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#88

Post by grif-fin »

venomsnake wrote: post #60
jshelly wrote: post #44

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

No. But with so much interesting things left to find I start to really really hate the concept of mortality :(

I could not agree more. Everyday I wake up and I think why is it that we gave up on massive wave of research on immortality/life extension.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#89

Post by delecti »

IanDrake wrote: post #69

Is the speed of light affected by the gravitational fluctuations mentioned in the article? Or, put another way, is the speed of light only a constant because we measure it in constant gravity?

Any observer will observe the same speed of light in their location.

Any effect of gravitational fluctuations in spacetime on the speed of light is a bit like a car driving on a race track that has treadmills scattered around it pointing in various directions and speeds. The car's speedometer will always read the same value because it's measuring the speed of its tires on whatever it's driving on.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#90

Post by yellow_postit »

bzbarsky wrote: post #79
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…

This thing was a billion light years away. Say it were closer; let's put it at a single light year away. LIGO measures wave amplitude, as far as I can tell, which goes down linearly with distance (unlike wave energy, which goes down quadratically, since it's proportional to square of the amplitude). So we could expect to see an effect about a billion times bigger. The detected effect was a change in metric of one par…

What I didn't understand after reading the article is how do they separate out a set of waves for one specific thing vs. the many other objects sending out waves. Is it just that the set of blackholes are the strongest set of waves and thus the ones we can detect?
Post reply on HN