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

141–150 of 502 posts

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#141

Post by kamaal »

jerf wrote: post #68
CGamesPlay wrote: post #24

Earlier quoted context omitted.

The amount of energy needed to transmit via a gravitational wave is INSANE. It would involve very rapidly accelerating and decelerating a black hole / neutron star. While it might be possible to do this, it's not within the realm of something we could accomplish without several orders of magnitude technology improvements, and possibly may not be physically possible at all (moving object that heavy that quickly might…

Even if it were possible, what sort of crazy alien would it take to burn 3 solar masses of negentropy to basically run a ping, compared to the amount of data that could be transmitted with electromagnetic waves with 3 solar masses of negentropy? It's literally dozens of orders of magnitude in difference. Any aliens that are that bad at engineering probably aren't going to grow to the point that they can shake neutron…

Our power generation stations are the black hole equivalent to the caveman with only access to generating fire through rubbing stones.

Based on what level of civilization you are. Rubbing two black holes in for a ping, might be the same as rubbing two stones for a spark. Advanced civilization go really advanced, to a point their activities would be undetectable to us or would appear to us the nature of reality itself.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#142

Post by ScottBurson »

tizzdogg wrote: post #127
losvedir wrote: post #4

> And then the ringing stopped as the two holes coalesced into a single black hole, a trapdoor in space with the equivalent mass of 62 suns. All in a fifth of a second, Earth time. Am I reading this correctly, that shortly after the detector came online we just happened to observe the exact moment a billion years ago that two black holes collided? Was that extremely coincidental? Or do these events happen all the tim…

I am not a physicist, and dont have a good mental model of gravitational waves (or general relativity at all), so maybe someone can answer my laymans question: do these waves behave like ripples in water, so a single event generates multiple repetitive, concentric waves permeating through space? That would make me think that a single massive event would be easier to detect because it would leave many repeated "echoes…

An echo is a reflection. I don't know whether gravitational waves can be reflected even in principle, but even if they can, space is so empty that in practice there's nothing to reflect them. So even a single massive event, like the one described in the article, will just send out a single expanding spherical wavefront; if you're not listening at the right moment, you'll miss it.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#143

Post by platz »

bzbarsky wrote: post #126
swombat wrote: post #103

Earlier quoted context omitted.

On the other hand, we may well detect the 3 solar masses radiated away as energy. That decreases as an inverse square law, so as one solar mass is about 10^30kg, and 1kg gives off about 10^17 J, we're talking about an explosion releasing something around 10^47 J. For comparison, a 1 kiloton nuclear bomb gives off about 10^15 J. So, inverse square that explosion... 1 light year is about 10^16m, so we square that and g…

The big question is how much of the energy would get transferred in practice. I agree that 3 solar masses worth of electromagnetic radiation at 1 light year distance would feel like a nuke going off. What I don't know is to what extent the energy of the equivalent gravitational waves (which _would_ have a lot of energy I agree) would actually get transferred to things we care about, like the atmosphere and us. If it'…

I would like to understand why a gravitational wave distorts length in relation to normal gravity wells; specifically is this particular to waves? Why don't lengths get distorted in a normal gravity well, or do they? In essence, what is different between a gravity wave and a gravity well, which i understand both distort space, but only the wave distorts it in a way we can measure? Does the gravity well change lengths proportionally in all directions and thus isnt measurable?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#144

Post by alkonaut »

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 (kind of) had to add the cosmological constant to GR just so the universe wouldn't collapse onto itself and instead be static. The idea of the unchanging universe was maybe partly due to personal or religious preconceptions. So at least in his mind the universe was static, which of course was proven "wrong" by the discovery that the universe is expanding. This was not a proper scientific theory of his, rather a preconception, like his aversion to the randomness of Quantum Physics (again, religion it appears).

Of course, being Einstein, he was again on the right side of the argument when the universe was much later discovered to be accelerating, again requiring a cosmological constant (or some similar fudge factor).

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#145

Post by stouset »

boardwaalk wrote: post #138

If they build a third observatory, can they triangulate where in the universe the events are occurring?

My intuition is that this is unlikely, but I'd love to see someone do the math. Given the scale of interstellar distances, any locations on our planet (and even in our solar system) are going to effectively function as a single point. Given arbitrarily-accurate measurement, it could work, but I'd bet physical limitations will prevent that from being a possibility.

To my mind, it'd be roughly like trying to triangulate an earthquake in France with three sensors in a 1mm^3 cube in NYC (scale is probably way off, I definitely didn't do the math).

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#146

Post by tizzdogg »

ScottBurson wrote: post #142
tizzdogg wrote: post #127

Earlier quoted context omitted.

I am not a physicist, and dont have a good mental model of gravitational waves (or general relativity at all), so maybe someone can answer my laymans question: do these waves behave like ripples in water, so a single event generates multiple repetitive, concentric waves permeating through space? That would make me think that a single massive event would be easier to detect because it would leave many repeated "echoes…

An echo is a reflection. I don't know whether gravitational waves can be reflected even in principle, but even if they can, space is so empty that in practice there's nothing to reflect them. So even a single massive event, like the one described in the article, will just send out a single expanding spherical wavefront; if you're not listening at the right moment, you'll miss it.

Sorry, "echo" wasnt the right term (hence my quotes).

What I am trying to ask is if these behave like concentric water ripples, where from a single event you get first one peak of a wave, followed by many more repeated concentric peaks gradually getting smaller in amplitude? It sounds like there is just a single momentary wavefront without any residual secondary waves? Why is that?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#147

Post by Florin_Andrei »

losvedir wrote: post #4

> And then the ringing stopped as the two holes coalesced into a single black hole, a trapdoor in space with the equivalent mass of 62 suns. All in a fifth of a second, Earth time. Am I reading this correctly, that shortly after the detector came online we just happened to observe the exact moment a billion years ago that two black holes collided? Was that extremely coincidental? Or do these events happen all the tim…

The coalescing and ring-down takes a fraction of a second. The fraction of a second refers to the duration of the event. It does not mean they caught an event a fraction of a second after they turned it on.

Here's a better article:

http://www.newyorker.com/tech/elements/gravitational-waves-e...

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#148

Post by ddingus »

xCathedra wrote: post #125

Could someone explain what possible applications this might produce?

It's super early, and detection seems at the limits of our technology.

This is just understanding at present. That, in itself is worth it.

As that understanding develops, and our tech advances, engineering may be able to apply it in useful ways, maybe object detection above a specified mass? New ways to visualize things?

One "application" is to serve as a ruler to measure out tech with. The limits are there, putting these observations just within reach.

Now that we have some confirmation, we also have the metrics as well as the compelling new science that may arise from all of this as a strong motivation to advance.

It's like being able to detect color for the first time. At first we understand what color is, then we refine, and after iterations, engineering, experiments, we get to a place where we see it all in color.

Applications will follow.

These waves being confirmed are like a new sense. Crude, but real. We can now follow this new perception to its conclusion, just as we have many other things.

We don't always know what that conclusion will be, or the form an application may take, but we do know we won't actualize any of it if we don't do the basic, hard, expensive work needed first.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#149

Post by lutorm »

tizzdogg wrote: post #127
losvedir wrote: post #4

> And then the ringing stopped as the two holes coalesced into a single black hole, a trapdoor in space with the equivalent mass of 62 suns. All in a fifth of a second, Earth time. Am I reading this correctly, that shortly after the detector came online we just happened to observe the exact moment a billion years ago that two black holes collided? Was that extremely coincidental? Or do these events happen all the tim…

I am not a physicist, and dont have a good mental model of gravitational waves (or general relativity at all), so maybe someone can answer my laymans question: do these waves behave like ripples in water, so a single event generates multiple repetitive, concentric waves permeating through space? That would make me think that a single massive event would be easier to detect because it would leave many repeated "echoes…

https://www.black-holes.org/gw150914 has some visualization of the event. There is the initial inspiral, and then there is a ringing afterwards. However, the entire event is over in a fraction of a second, which may be a "blip" to humans, but is very long when things happen at the speed of light.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#150

Post by Florin_Andrei »

stouset wrote: post #145
boardwaalk wrote: post #138

If they build a third observatory, can they triangulate where in the universe the events are occurring?

My intuition is that this is unlikely, but I'd love to see someone do the math. Given the scale of interstellar distances, any locations on our planet (and even in our solar system) are going to effectively function as a single point. Given arbitrarily-accurate measurement, it could work, but I'd bet physical limitations will prevent that from being a possibility. To my mind, it'd be roughly like trying to triangulat…

It would work. The delta-t is a few miliseconds. This gives enough precision for a decent estimate of the direction of the signal.

Now estimating the distance is a different matter.

Post reply on HN