# Krauss on gravitational waves

February 12, 2016 • 1:15 pm

If you’re interested in the stunning announcement of gravitational waves yesterday, do read Lawrence Krauss’s piece about it in the New York Times, “Beauty in the darkness.” He’s the expert here, so I’ll just give an excerpt. I should add that this observation provides evidence not just for gravitational waves, but also for black holes:

To see these waves, the experimenters built two mammoth detectors, one in Washington State, the other in Louisiana, each consisting of two tunnels about 2.5 miles in length at right angles to each other. By shooting a laser beam down the length of each tunnel and timing how long it took for each to be reflected off a mirror at the far end, the experimenters could precisely measure the tunnels’ length. If a gravitational wave from a distant galaxy traverses the detectors at both locations roughly simultaneously, then at each location, the length of one arm would get smaller, while the length of the other arm would get longer, alternating back and forth.

To detect the signal they observed they had to be able to measure a periodic difference in the length between the two tunnels by a distance of less than one ten-thousandth the size of a single proton. It is equivalent to measuring the distance between the earth and the nearest star with an accuracy of the width of a human hair.

If the fact that this is possible doesn’t astonish, then read these statements again. This difference is so small that even the minuscule motion in the position of each mirror at the end of each tunnel because of quantum mechanical vibrations of the atoms in the mirror could have overwhelmed the signal. But scientists were able to resort to the most modern techniques in quantum optics to overcome this.

The two black holes that collided, which the LIGO experiment claimed to have detected, were immense. One was about 36 times the mass of our sun, the other, 29 times that mass. The collision and merger produced a black hole 62 times our sun’s mass. If your elementary arithmetic suggests that something is wrong, you’re right. Where did the extra three solar masses disappear to?

Into pure energy in the form of gravitational waves. . .

## 40 thoughts on “Krauss on gravitational waves”

1. Merilee says:

Sub

2. allison says:

“It is equivalent to measuring the distance between the earth and the nearest star with an accuracy of the width of a human hair.”

-I suppose Krauss meant the nearest star other than our Sun?

1. Kevin says:

Yes, quickly I estimate:

hair/sun: 1/10^14
hair/alpha centauri: 1/10^21

The recent binary black hole merger had signals of “a peak gravitational-wave strain of 1.0 × 10−21”

Note, the proton radius is 0.8*10^-15 m. Holy CC, what they measured was small.

So for a biologist, it was equivalent to measuring the distance to the Milky Way center and see a twitch in a Pinkah finger?

I see the exit over there…

3. ashdeville says:

I’m fairly sure that jesus, god, the Holy Spirit and all the rest of them just felt that gap in which they exist get ever so slightly smaller.

1. gravelinspector-Aidan says:

It’s not a gap ; it’s a mesh of gaps spaced at 10^-21m intervals.
God-puree. Quantum god-puree.

4. JonLynnHarvey says:

I’m a bit confused on the status of evidence for black holes. I thought there were several dozen fairly strongly confirmed candidates for black holes already, including Sagittarius A at the center of our own galaxy. However, it appears there is still the possibility of a different interpretation.

Oddly, science fiction movies about black holes are consistently among the worst science-fiction movies ever as if the black hole was sucking in the writing quality. A friend of mine with a doctorate in astrophysics said “Interstellar” is probably (relatively) the best black hole movie, but there is very little competition.

Although Kip Thorne was an advisor on “Interstellar”, his ideas were meddled with and Lawrence Krauss called the science miserable and decried their meddling with Thorne’s advice.

Since Lawrence Krauss wrote a terrific book on “The Physics of Star Trek” (concluding that a modest majority of the physics is pretty good, but a fair amount is bogus), perhaps he can weigh in sometime on the egregious scientific horrors of virtually every black hole-themed scifi movie ever and suggest what a good one might be like. (But after Thorne’s advice in “Interstellar” was messed with, he may not want to.)

Yes, there were candidates, meaning there were alternative albeit more unlikely explanations.

The best evidence I have read (though mind I’m a layman here) was ironically an observation of a gas clump falling into a SMBH a few months back. They have increased resolution so they could tell that there was tension with the central mass being a dead star aggregate. I.e. the gas “death scream” was definitely cut short, and the thermal emission of the center didn’t increase enough to have the gas coating a surface.

But there were alternatives there too at a guess, for example having the swarm of mass inevitably orbiting the central mass shrouding the infall process, et cetera.

Mind, I don’t think the astronomers and physicists involved was leaning on alternatives much, the candidates was accumulating.

But this seems to be the first time conventional mass models don’t cut it, seeing the descriptions. I don’t know exactly how, and I could have missed the explanation in the mass of LIGO papers on this, but I can guess FWIW.

The dynamic model reproducing the signal “chirp” has the gravitation deform and relax the event horizon I think seeing the simulations, not entire neutron stars. So I guess the chirp from star collisions would have a different signature, especially perhaps the settling at the end where a merged star could plausibly continue to ring for some time.

Adding weak evidence, telescopes pointed that way saw zip.

On another matter, my cut of terrific Star Trek physics goes at the sound effects. The Bad Astronomer talks about “sound in space”. (Which only happens in dense gas clouds, and wouldn’t be audible at many thousands of km wavelengths.) But the “ears” of the camera observer mocks a space suit (say), and precisely these GW chirps would be audible in a spaceship orbiting the BH merger by their tug on the ears. (Claimed during the press conference, by the way!) So who knows what the field physics of Star Trek can do?

I hope Krauss does better than the Bad Astronomer!

2. gravelinspector-Aidan says:

Although Kip Thorne was an advisor on “Interstellar”, his ideas were meddled with and Lawrence Krauss called the science miserable and decried their meddling with Thorne’s advice.

Someone who was a science advisor to a film about then (it may have been Thorne, I don’t remember) made the point that he got paid for giving advice, but the contract didn’t say that the studio would take it.

5. Kevin says:

They are trying to compare whether they felt pain, joy, pleasure, discomfort, luck, misfortune. Whatever?!.

I am beginning to wonder if astrology, i.e., astronomical influences, on our lives is hardwired into some people.

6. EvolvedDutchie says:

When two black holes love each other very much… we detect ripples in spacetime.

7. veroxitas says:

I have read the article “Finding Beauty in the darkness” by Krauss which Prof. Coyne referenced. Toward its end the author says – “Ultimately, ——- we may learn more about ——- the possible existence of other universes.”.
Can someone explain in fairly lay terms (no higher than upper school physics!!) how it would be possible to access information such as that?

1. JJH says:

“Can someone explain in fairly lay terms (no higher than upper school physics!!) how it would be possible to access information such as that?”

As far as I can tell, the answer to your question would be, no (I speak humbly for me, future generations will no doubt accomplish more than I ever imagined). There are some really brilliant physicists working on it, but if they find the answer it will probably be (much like the gravitational wave problem), pretty mathematical intensive and rely on observational evidence not understandable to the average lay reader. However, if the empirical evidence (there are multiple models that predict it) does begin to emerge, it will be tested and retested and argued over until the preponderance of the evidence makes it unreasonable to deny.

2. Just a wild guess from a layperson … if there were a cataclysmic event in a nearby universe, could it be that the resulting cosmic ripples might be detectable and discernible from ‘local’ events? Perhaps that could provide cosmologists a clue as to where to look in the Void.

1. JJH says:

It is well beyond my level of expertise, but I believe they are looking for anomalies at the edge of the observable universe for clues.

1. veroxitatis says:

Thanks. But surely there is a very large part of our universe which will forever be outside of our light cone and we shall have no way of accessing the information which makes up a universe or universes beyond our only partially knowable universe?

I don’t think he meant anything specific, but that learning about how spacetime behaves in strong gravity conditions near or in black holes teach us more physics relevant for cosmology of the early universe. There are cosmologies where universes “bud off” naturally, including the current accepted one, and perhaps we can learn more on that or even come up with more tests.

[Believe it or not, there are now tests for collisions of universes! Sean Carroll’s blog has articles on that. Our universe seems more stirred than shaken from collisions though.]

4. gravelinspector-Aidan says:

Can someone explain in fairly lay terms (no higher than upper school physics!!) how it would be possible to access information such as that?

I’m not at all sure if this is a position that Lawrence Krauss takes, but try this or size.
One of the big unknowns about the universe is why gravity is so weak. Around 10^-40 times the strength of the other forces. One proposition to explain this is that gravity leaks from the 4 dimensional spacetime that we inhabit through some other dimension of measure, and has it’s main effects off in some higher dimension of space-time.
3 solar masses converted in energy in under a second. That has got to smart.

8. JJH says:

“Too often people ask, what’s the use of science like this, if it doesn’t produce faster cars or better toasters. But people rarely ask the same question about a Picasso painting or a Mozart symphony.”

I just think that is priceless!

1. Tim Harris says:

A pity you didn’t quote what followed.

2. Tim Harris says:

I might add that one constantly sees science being justified by scientists, or those who take an interest in science (and on this website, too), on precisely the grounds that it does produce faster cars and better toasters – objects that may stand in metonymically for ‘progress’.

1. JJH says:

Tim,

That is a fascinating point. But, I wonder how much of the practical application aspect is brought on by necessity and not by what really motivates the dedicated men and women who perform the hard work?

I mean I can get instant gratification from a Dali painting or Miles Davis rift without any effort; but a super nova or genetic drift, they only take on beauty when you really look at how we discovered them.

I believe people in the knowledge arts frequently use practicality out of necessity, but I don’t think it is what motivates them nor is it why I think humanity should appreciate the beauty of the art.

1. Tim Harris says:

No, surely it is not first of all a desire to contribute in some practical way to progress, nor a desire to contribute to some heap called knowledge (as opposed to opinion), but a burning interest in why and things came to be the way they are that motivates good scientists.

1. Tim Harris says:

‘why and HOW things came to be…’

2. Tim Harris says:

Just in case what I am pointing out is being misunderstood, I in no way agree with those including scientists, who seek to justify science in terms of its practical application.

2. This is hardly the time or place for a flare-up in the “two cultures” war.

My sense is that scientists who appeal to practical results do not appeal to mundane frivolities like toasters. They usually point to advances with much more gravitas. Life-saving medicine, etc.

1. Tim Harris says:

There is no flare-up. I was simply immensely pleased to see Lawrence Krauss eschewing the culture wars.

2. Tim Harris says:

And in fact, pace Krauss & JJH, a lot of people ask what is the use of a Picasso painting or a Mozart symphony. Robert Schumann had a word for them.

9. Tim Harris says:

I like and respect this statement:

‘Too often people ask, what’s the use of science like this, if it doesn’t produce faster cars or better toasters. But people rarely ask the same question about a Picasso painting or a Mozart symphony. Such pinnacles of human creativity change our perspective of our place in the universe. Science, like art, music and literature, has the capacity to amaze and excite, dazzle and bewilder. I would argue that it is that aspect of science — its cultural contribution, its humanity — that is perhaps its most important feature.’

1. Indeed. That’s a great statement.

I’d suggest that there’s something off with people who can’t see the aesthetic value in scientific knowledge. When you really grok some of this stuff it can be as moving as any piece of art or music.

1. Tim Harris says:

I wholly agree.

2. Tim Harris says:

Well, not wholly, actually, since I’m not fond of the word ‘aesthetic’ which has all too often the effect of sticking things in some little, bounded aesthetic space, somewhat like a pretty little black hole, from which no implications or considerations that might have a bearing on the rude world outside may issue.

3. gravelinspector-Aidan says:

Oh Ceiling Cat, save us from the grokless hordes.

Having had time to look briefly at the slew of papers that the LIGO collective has published on their site, I find it amazing how much physics and astronomy has already been extracted from a single observation.

[I’ll tentative add Hawking’s claim of successful test of his area theorem of BHs, but it wasn’t in there.]

So when Krauss says “What more can we learn about the universe … anyone’s guess” I reflect that they have learned:

– The frequency of detectable events.

Seems Kip Thorne’s claim of nearly 1000/year is based on a detection analysis of the first run. They will see ~ 30 events/year from the current sensitivity, meaning the 3 times more sensitive “a^2LIGO” will see what Thorne said. (And the early detection was a lucky event, I take it. That paper was just too much a read too late in the evening.)

– There is something strained in current astrophysics of large stars.

To have 30 solar mass stars go black hole, they need to have little solar wind. That could happen for low metallicity stars at < 1/2 Sun's metallicity. Now they need to find that much low metallicity clouds near us, and science the shit out of star models!

[And then they can look further out, the rate of BH mergers should go up. By the way, I think from that read that having 30 solar mass stars at the end of their lifetime was even more untested than having BHs was!]

Did I say I was amazed!?

1. Tim Hsrris says:

I hugely enjoy your enthusiastic contributions, Torbjorn (without the umlaut – forgive me!).

2. Tim Harris says:

I hugely enjoy your enthusiastic comments, Torbjorn (without the umlaut – if you call it that – forgive me!).

11. will says:

Regarding:

The two black holes that collided, which the LIGO experiment claimed to have detected, were immense. One was about 36 times the mass of our sun, the other, 29 times that mass. The collision and merger produced a black hole 62 times our sun’s mass. If your elementary arithmetic suggests that something is wrong, you’re right. Where did the extra three solar masses disappear to?

Into pure energy in the form of gravitational waves. . .

———

Are gravitational waves “pure energy”? Can all waves be thought of in terms of a particle/wave duality? Or just light?

1. Zetopan says:

“Are gravitational waves “pure energy”?”

That depends on what you mean by “pure”. Gravitational waves are ripples in space-time. Energy is required to make ripples in space-time. Hence ripples in space-time are one form of energy. Electrons and photons are also forms of energy.

“Can all waves be thought of in terms of a particle/wave duality? Or just light?”

All elementary particles, and this includes light (photons), electrons, protons, etc., exhibit wave/particle duality.

Since mass and energy are equivalent, the larger the mass the shorter the wavelength. Since a proton at rest has much more mass than an electron, it also has a much shorter wavelength than an electron. On the other hand, a sufficiently accelerated electron could have more energy and thus a shorter wavelength than a proton at rest.

The wavelength of the Earth is *very* small since the mass is so great. Likewise, everyday objects (people, toasters, safety pins, toast crumbs, etc.) have longer wavelengths than the Earth but are still so very short that they are perceived as “solid objects”.

You as a person occupy a region in space-time and the reality is that you are spread out over a *very* small additional region since the elementary particles that you are composed of are also spread out. This spreading is *far* too small to be visible. Hence you appear to be in one specific location relative to our senses.

Every particle in your body has a probability of being located at a significant distance from its “nominal” location, but that probability becomes vanishingly small as the distance increases.

Your entire hand could be located at Alpha Centauri for a second, but the probability is so small that you can consider it to be zero. That is also true for it being located on the opposite side of your body or in the next room. Quantum mechanics is not exactly “intuitive” but experiments have shone that it is *very* accurate.