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

The Absurdity of Detecting Gravitational Waves (2017) [video]

youtube.com

Post reply on HN
Print view View original

51–60 of 63 posts

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#51

Post by akvadrako »

perl4ever wrote: post #41
a1369209993 wrote: post #18

Earlier quoted context omitted.

Communication is a red herring; the actual Fermi paradox is why huge sections of the night sky aren't black[0] due to all the stars being enclosed by Dyson spheres. Or, for that matter, why the planet hasn't been eaten by von Neumann swarms yet. 0: technically a uniform dim infrared of waste heat

I thought that huge sections of the night sky are empty - we call them Cosmic Voids. See: https://en.wikipedia.org/wiki/Void_(astronomy)

Empty isn't the same as black. Dyson spheres would be emitting lots of infrared radiation.

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#52

Post by akvadrako »

spuz wrote: post #32
ci5er wrote: post #16

Earlier quoted context omitted.

> But why do humans find this idea so seductive? It's because of an underlying loneliness: we want to believe that we are connected with the universe in some fashion, that our existence has a point [...] No. It's simply that statistically, we can't believe we are the first, nor that we are unique. It would be (statistically) extremely odd if we were, and there is a bias against anthropo-centric theories. Heck, I'd be…

> No. It's simply that statistically, we can't believe we are the first, nor that we are unique. It would be (statistically) extremely odd if we were, and there is a bias against anthropo-centric theories. Fermi's paradox does not ask about civilisations like ours. It asks about interstellar travelling or at least interstellar communicating species. We have not achieved this level yet so we are not the 'first' as you…

Well one answer to the Fermi paradox is we get wiped out but barring that it seems unlikely we won't reach the stars in millions of years.

And you seem to ignore it, but the other part of the paradox is if we can achieve interstellar travel in millions of years, that's like no time at all on a galactic scale. So it would be a major coincidence if we are within 1 million years of the first.

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#53

Post by stultifying »

AnsisMalins wrote: post #48
mysterypie wrote: post #47

I figured that one tube is stretched by the gravitational waves and the perpendicular tube is unaffected, so you're measuring the difference between the two tubes. Simple and easy to understand. However, the video mentioned that both light and the detection apparatus are stretched by the same degree and the physicist says "the light does get stretched and that part doesn't do the measurement for us"[1] -- which makes…

Light takes different amounts of time to travel down the stretched vs squeezed tube.

Yes, the speed of light cannot exceed its limitation, and as one channel stretches in length, it simply requires more time to travel that length at the constant maximum speed.

The fixed channel remains the same, and covers the unstretched distance, so the light, traveling at the same constant speed reaches the end of the unchanged channel within less time than the other channel.

Or invert the same effect for cases where one channel is compressed to a shorter length, since waves oscillate. So both circumstances may be encountered. Some photons will traverse a compressed distance at a fixed speed, other photons will traverse a stretched distance. Meanwhile, the other perpedicular path is neither stretched nor squashed, and the photons in that channel demostrate the difference when compared to the effected channel.

So no matter what happens, the rate of travel is locked at the upper limit of 186,000 miles per second, whether all of space, energy and matter is squashed in a slightly smaller volume, or expanded to fill a slightly larger volume, the relativistic distances do not change, and the rate of passage of time does not change.

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#54

Post by spacenick88 »

a1369209993 wrote: post #18
TomMckenny wrote: post #4

I wonder if gravity wave detection could be ever be precise enough for communication. I wonder this because it occurs to me that one possible answer to Fermi's paradox is that aliens don't use Radio or other EM to chat. And maybe they don't leak it because they move energy and information around more efficiently than we do.

Communication is a red herring; the actual Fermi paradox is why huge sections of the night sky aren't black[0] due to all the stars being enclosed by Dyson spheres. Or, for that matter, why the planet hasn't been eaten by von Neumann swarms yet. 0: technically a uniform dim infrared of waste heat

To me Dyson spheres seem decidedly low tech. Why do we think a very advanced alien species would a) even need such an amount of power b) use such a primitve method as wrapping a star in solar panels?

The only stuff I can imagine needing such energy levels would be wormhole gates or Alcubiere drives. Powering the former with a Dyson sphere might make sense but the latter would have to fit on a ship.

The interstellar aliens I find more realistic would be those that just mastered cryo sleep or general AI and built seed ships. We don't really have any way of detecting those, do we?

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#55

Post by spuz »

akvadrako wrote: post #52
spuz wrote: post #32

Earlier quoted context omitted.

> No. It's simply that statistically, we can't believe we are the first, nor that we are unique. It would be (statistically) extremely odd if we were, and there is a bias against anthropo-centric theories. Fermi's paradox does not ask about civilisations like ours. It asks about interstellar travelling or at least interstellar communicating species. We have not achieved this level yet so we are not the 'first' as you…

Well one answer to the Fermi paradox is we get wiped out but barring that it seems unlikely we won't reach the stars in millions of years. And you seem to ignore it, but the other part of the paradox is if we can achieve interstellar travel in millions of years, that's like no time at all on a galactic scale. So it would be a major coincidence if we are within 1 million years of the first.

As far as the Fermi paradox is concerned it's a much safer assumption to make that advanced civilisations will achieve interstellar communication before they achieve interstellar travel.

Even so, my point is that human technology tells us nothing about the probility of a civilisation ever developing interstellar communication because we haven't seen it happen yet. We are still at the 0 stage when going from 0 to 1. It doesn't make sense to extrapolate from our position on the technological timeline. It makes more sense to assume tabula rasa that aliens have developed this technology and then explore the implications of that.

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#56

Post by LoSboccacc »

roywiggins wrote: post #38
meowface wrote: post #5

Earlier quoted context omitted.

Even if tons of intelligent civilizations happened to be radiating gravitational waves (or some other form of radiation which travels at or very close to the speed of light) encoded with information directly towards Earth right now, it's very likely we'd never receive them in the next million years due to the vastness of the universe.

What about all of the intelligent civilizations who were doing it a million years ago? With a million years for waves to fill space, you'd think we'd be able to hear something.

Not necessarily, immagine scanning all radio frequencies except you don’t know neither modulation nor the symbols transmitted.

Separating something from noise is a challenge on itself especially if signals are compressed or encrypted

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#57

Post by bajsejohannes »

One thing the book Black Hole Blues (Janna Levin) brought home to me was the absurdity of actually getting this project done. Now that it's complete, it's easy to say that it was obviously a good idea. It's another thing entirely to bet huge budgets on something that doesn't seem very likely to succeed.

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#58

Post by Certhas »

mysterypie wrote: post #47

I figured that one tube is stretched by the gravitational waves and the perpendicular tube is unaffected, so you're measuring the difference between the two tubes. Simple and easy to understand. However, the video mentioned that both light and the detection apparatus are stretched by the same degree and the physicist says "the light does get stretched and that part doesn't do the measurement for us"[1] -- which makes…

The subtlety is this:

Imagine you are in the weightlessness of space, and you measure distances by taking a ruler and placing unconnected beads 10 cms apart.

Now a gravitational wave passes through, what do you see? Nothing. The beads don't move. The intervals you use to measure the distance are stretched in the same way as the space you want to measure in the first place.

So what you can do is, every milisecond or so you lay a new string of beads into empty space. And now when a gravitational wave passes through you'll see that when you lay the string of beads at the moment the gravitational wave passes it doesn't line up with the previous ones.

That you can measure. And by observing the miniscule misalignment of the beads you can see stretching that is much smaller than the 10cm intervals.

So the strings of beads are light rays, and their intervals are the wavelength. The difference is that they don't last, but if there is a light ray in there right as the tube is stretched, it get's stretched along with the tube and you would not see a difference with that, whereas the light that's coming right after it will place new beads/amplitude peaks and actually see the stretched distance.

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#59

Post by v_lisivka »

ArtWomb wrote: post #21

No concrete data on actual funding increases, but it appears the success of LIGO and gravity wave detection has kicked off a renaissance in basic research into fundamental theories of gravitation itself. With a space-based gravity wave detector in various stages of development. And the possibility that gravitons have been indirectly observed already. Is Gravity Quantum? https://www.scientificamerican.com/article/is-g…

LIGO is scaled up version of Michelson-Morley experiment, so we should ask very different kind of question.

Re: The Absurdity of Detecting Gravitational Waves (2017) [video]

#60

Post by effie »

akvadrako wrote: post #51
perl4ever wrote: post #41

Earlier quoted context omitted.

I thought that huge sections of the night sky are empty - we call them Cosmic Voids. See: https://en.wikipedia.org/wiki/Void_(astronomy)

Empty isn't the same as black. Dyson spheres would be emitting lots of infrared radiation.

Which would be hard to detect, if they had temperature close to that of CMB.
Post reply on HN