Author Topic: Gravitational waves: rumors of their discovery  (Read 4976 times)

Re: Gravitational waves: rumors of their discovery
« Reply #30 on: February 13, 2016, 12:09:01 PM »
I'm not sure about those two ideas except to say they are different phenomena. A wave is produced by some mechanism: for instance plunge your finger slightly into the water and pull it up and down and you will create waves that expand circularly. Gravitational waves are a version of that with two black holes rapidly rotating about each other, disrupting enough the fabric of space-time to give g-waves strong enough for us to detect. OTHO, a clock is an apparatus that ticks. A pendulum can make a repeated tick; your wristwatch has rotating wheels to make a succession of ticks, etc. Your question: can you take g-waves into some kind of apparatus that would produce a succession of ticks ( that is, a clock)? Perhaps, but I haven't the slightest idea how that would be done.

I guess the theory is that gravity operates at some frequency range similar to how sound, radio or light does. Gravity just works at much higher frequency than any of those. In order to detect, manipulate or reproduce those things you need a receiver or transmitter capable of reproducing the same frequency range of whatever it is you want to observe or reproduce. If gravity does operate at some frequency range then the easiest way to detect or reproduce it would require a clock capable of accurately reproducing that frequency range. What I don't know is if we currently believe that gravity operates at some really high frequency range, or if that line of thought has been rejected since I was at the MDSCC.

From what I understand about LIGO they are getting around the need for more accurate clocks by comparing the differences between two distantly separated receivers. It works. Barely. But it would be much more accurate and they would be able to see a lot more with higher frequency clocks at the two receivers.
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Offline josephpalazzo (OP)

Re: Gravitational waves: rumors of their discovery
« Reply #31 on: February 13, 2016, 01:02:49 PM »
I guess the theory is that gravity operates at some frequency range similar to how sound, radio or light does. Gravity just works at much higher frequency than any of those. In order to detect, manipulate or reproduce those things you need a receiver or transmitter capable of reproducing the same frequency range of whatever it is you want to observe or reproduce. If gravity does operate at some frequency range then the easiest way to detect or reproduce it would require a clock capable of accurately reproducing that frequency range. What I don't know is if we currently believe that gravity operates at some really high frequency range, or if that line of thought has been rejected since I was at the MDSCC.

From what I understand about LIGO they are getting around the need for more accurate clocks by comparing the differences between two distantly separated receivers. It works. Barely. But it would be much more accurate and they would be able to see a lot more with higher frequency clocks at the two receivers.

It's not a question of being at a high frequency. For a clock to work, you need regular beats. Now atomic clocks work on QM principles that the energy levels in any atom are quantized, It's like a vending machine that accepts only 1¢, 5¢. 10¢ and 25¢. So if you try anything else it won't accept it. So, using this concept in QM with atoms for which you know precisely the energy levels, you can build clocks that are precise and reliable. In the case of g-waves, the objects producing them - black holes, for instance- you have no way of knowing if the beats that are coming in will be regular, that is the time between each beat would have to be exactly the same within a certain margin of error. Two black holes can speed up or down depending what's in their immediate environment, hence that process would not be reliable. So I guess the trick would be to manufacture these g-waves that would give you regular beats and strong enough to register on your counter, but how, since rotating black holes themselves gives waves that are so weak you need to build something the size of LIGO to detect them!!

Offline trdsf

Re: Gravitational waves: rumors of their discovery
« Reply #32 on: February 13, 2016, 01:14:16 PM »
See section on Frame Dragging ... this is also confirmed ...
https://en.wikipedia.org/wiki/Tests_of_general_relativity

On the other hand my vote is with Dark Matter and Dark Energy ... which I don't see as quantum effects IMHO, since they are large scale phenomena.
Dark matter and dark energy are already accounted for in General Relativity, under the term Λ (lambda) -- originally introduced as the cosmological constant when he was trying to construct a static model of the universe.  After Hubble, he just set it to zero, but the discovery of the accelerating expansion of the universe makes it possible that Λ is not zero after all.  At a minimum, the effects of dark matter and dark energy can be treated mathematically as Λ in GR, even if they're not an actual structural alteration of space itself.
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Online Baruch

Re: Gravitational waves: rumors of their discovery
« Reply #33 on: February 13, 2016, 07:45:57 PM »
Dark matter and dark energy are already accounted for in General Relativity, under the term Λ (lambda) -- originally introduced as the cosmological constant when he was trying to construct a static model of the universe.  After Hubble, he just set it to zero, but the discovery of the accelerating expansion of the universe makes it possible that Λ is not zero after all.  At a minimum, the effects of dark matter and dark energy can be treated mathematically as Λ in GR, even if they're not an actual structural alteration of space itself.

Except that is a cop-out.  Lambda is a cheat.  GR is wrong anyway, since QFT is right.  Like fighting over the scraps left over from Newtonian physics.  SR/GR is classical ... if Lambda explains everything, why are theoreticians and experimenters looking deeper?
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Offline josephpalazzo (OP)

Re: Gravitational waves: rumors of their discovery
« Reply #34 on: February 14, 2016, 11:44:15 AM »
Dark matter and dark energy are already accounted for in General Relativity, under the term Λ (lambda) -- originally introduced as the cosmological constant when he was trying to construct a static model of the universe.  After Hubble, he just set it to zero, but the discovery of the accelerating expansion of the universe makes it possible that Λ is not zero after all.  At a minimum, the effects of dark matter and dark energy can be treated mathematically as Λ in GR, even if they're not an actual structural alteration of space itself.

Characterizing the cosmological constant Λ as an introduction can lead to some misinterpretation, especially those who have a superficial understanding of GR. Λ comes out of the solution to the Einstein Equations. It's legitimate, and not a cop-out solution (I know you didn't say but someone else did). What the theory doesn't do is set a value to it. That leaves it open to be determined by observation. As it stands today its value is  of the order of 10-29g/cm3, in metric units.

Offline trdsf

Re: Gravitational waves: rumors of their discovery
« Reply #35 on: February 16, 2016, 04:16:05 PM »
Except that is a cop-out.  Lambda is a cheat.  GR is wrong anyway, since QFT is right.  Like fighting over the scraps left over from Newtonian physics.  SR/GR is classical ... if Lambda explains everything, why are theoreticians and experimenters looking deeper?
Wrong again.

Lambda was a 'fudge factor' when Einstein inserted it in order to get the static universe he assumed and was ignored after Hubble, and only in light of the discovery of accelerating expansion has it been revived.  It's not meant to explain anything, it's descriptive, and the research is to determine if it actually does have a value, what value it has, and if it's non-zero, why it's non-zero.  I really shouldn't have to explain this.

You're also incorrect in saying GR is wrong and QM is right -- if Quantum Field Theory were right and General Relativity were wrong, then QFT would already be a theory of quantum gravity, and it is not.

GR has yet to be invalidated by an observation -- all we can say is that we know where it breaks down, not that it's incorrect.  And what we know is that both of them give nonsensical answers when they're combined.  What's most likely is not that either one is wrong, but that both are incomplete, just like Newtonian gravity was incomplete.  That incompleteness didn't make Newton useless: we still don't need anything more than Newton to calculate the flights of every spacecraft we've ever launched.  Using Einstein would only make matters unnecessarily complex, and the additional couple of decimal places gained would be irrelevant.

Whatever theory manages to combine GR and QM is going to have to duplicate their results at sufficiently low energy levels, with considerable accuracy, because we have already measured both those theories with considerable accuracy, and it doesn't matter if it's string theory, M theory, or something no one has come up with yet.  Both GR and QFT are approximations, but they are deeply and profoundly accurate approximations, and any unified theory has to be at least as accurate as both.

Keep in mind also that 'dark energy' and 'dark matter' are just labels: they don't explain anything either.  They mark the place where researchers have observed something, and don't know what it is yet, but they know something is there.  There's nothing wrong with placeholders in science -- those are the things that need further observations and research, after all.
"It's hard to be religious when certain people are never incinerated by bolts of lightning." -- Calvin and Hobbes
"I thought I committed regicide today, but I committed deicide!" -- Sadie Doyle, Beyond Belief

Offline josephpalazzo (OP)

Re: Gravitational waves: rumors of their discovery
« Reply #36 on: February 16, 2016, 06:42:58 PM »
@trdsf

The cosmological constant is about 10-9joules per m3  in order to account for the observed acceleration of the universe. If you calculate the equivalent of a 100-watt light-bulb (3.6 x 105 joules), you would need to harvest the energy of a sphere of a 44km- or 27.5 mile-radius. And that's not counting the energy required to harvest that energy, which probably would make that enterprise a no go. The other interesting feature is that if you calculate the vacuum energy from QFT, it is 10113 joules per m3, that is, 10124bigger than the cosmological constant - that mismatch bears the name of the vacuum catastrophe.

Offline trdsf

Re: Gravitational waves: rumors of their discovery
« Reply #37 on: February 16, 2016, 09:42:31 PM »
@trdsf

The cosmological constant is about 10-9joules per m3  in order to account for the observed acceleration of the universe. If you calculate the equivalent of a 100-watt light-bulb (3.6 x 105 joules), you would need to harvest the energy of a sphere of a 44km- or 27.5 mile-radius. And that's not counting the energy required to harvest that energy, which probably would make that enterprise a no go. The other interesting feature is that if you calculate the vacuum energy from QFT, it is 10113 joules per m3, that is, 10124bigger than the cosmological constant - that mismatch bears the name of the vacuum catastrophe.
Thank you, that was the prediction mismatch that I was trying to remember and couldn't, so I left it out rather than get it wrong.  I knew it was on the order of 10120, which is a hell of a miss.  Even astronomers -- who can get away with with a discrepancy of some 300 billion in their estimate of the total number of stars in this galaxy -- would be embarrassed by a miss that wide.  :)
"It's hard to be religious when certain people are never incinerated by bolts of lightning." -- Calvin and Hobbes
"I thought I committed regicide today, but I committed deicide!" -- Sadie Doyle, Beyond Belief

Offline josephpalazzo (OP)

Re: Gravitational waves: rumors of their discovery
« Reply #38 on: February 19, 2016, 05:46:41 PM »
Thank you, that was the prediction mismatch that I was trying to remember and couldn't, so I left it out rather than get it wrong.  I knew it was on the order of 10120, which is a hell of a miss.  Even astronomers -- who can get away with with a discrepancy of some 300 billion in their estimate of the total number of stars in this galaxy -- would be embarrassed by a miss that wide.  :)

According to this paper, Cosmological constant and vacuum energy: old and new ideas, the discrepancy has been reduced to 55 orders of magnitude, mainly due to the discovery of the Higgs boson, but still a long way to go...

Re: Gravitational waves: rumors of their discovery
« Reply #39 on: February 25, 2016, 11:05:23 AM »

Offline josephpalazzo (OP)

Re: Gravitational waves: rumors of their discovery
« Reply #40 on: February 25, 2016, 11:36:19 AM »


Good explanation from Brian Greene. Just a minor beef: these gravitational waves are ripples in spacetime, not in space. It's a common mistake that is often overlooked. But Greene should know better... I'm just knit-picking...

Online Baruch

Re: Gravitational waves: rumors of their discovery
« Reply #41 on: February 25, 2016, 12:44:58 PM »
I am no fan of Dr Greene.  But I am even less a fan of Dr Kaku.  There is subtle difference between popularizing science, dumbing-down science and science boosterism.  I really like the old book by Gleick on Chaos.
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Re: Gravitational waves: rumors of their discovery
« Reply #42 on: March 10, 2016, 02:47:55 AM »
Gravitational waves propagate at light speed just as photons but do they have an infinite life
span like them also ? If they do then presumably they carry on travelling through space time
right up until the heat death of the universe. The two black holes which collided were not the
same size so why did the large one not absorb the small one ? Was this because the collision
did not actually happen at its event horizon ? Which is only where one can absorb any matter 
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Online Baruch

Re: Gravitational waves: rumors of their discovery
« Reply #43 on: March 10, 2016, 07:36:14 AM »
Gravitational waves propagate at light speed just as photons but do they have an infinite life
span like them also ? If they do then presumably they carry on travelling through space time
right up until the heat death of the universe. The two black holes which collided were not the
same size so why did the large one not absorb the small one ? Was this because the collision
did not actually happen at its event horizon ? Which is only where one can absorb any matter

Good questions ... the conventional answer is that photons and gravitons (if gravity is quantized) travel until they are absorbed.  They don't literally go on forever ... but not-forever can be a long time.  That is why we can see "light" from the 3K event (Big Bang cooling).  By intercepting that light, we have murdered some innocent photons.

Collisions between Black Holes would be complicated ... the stuff outside the Black Hole, some of it will be absorbed by the combined Black Hole, and some of it will not.  This includes spiraling hot matter (X-ray hot) and gravitons.
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Offline josephpalazzo (OP)

Re: Gravitational waves: rumors of their discovery
« Reply #44 on: March 10, 2016, 02:10:50 PM »
Gravitational waves propagate at light speed just as photons but do they have an infinite life
span like them also ? If they do then presumably they carry on travelling through space time
right up until the heat death of the universe.


For the photon, and for any other particle with zero mass, time is a meaningless concept.

Quote
The two black holes which collided were not the
same size so why did the large one not absorb the small one ? Was this because the collision
did not actually happen at its event horizon ? Which is only where one can absorb any matter 

The signal we get is too faint to know what is really going on. It will be one of the challenges to figure out what the g-waves say. But already we can tell it's two rotating massive objects - the strength of the collision created a gravitational field so strong that it distorted space-time in waves that spread throughout space about 50 times stronger than all the stars and galaxies in the universe.