Physics Discussion Thread

SriKumar · Post by **SriKumar** » 13 Feb 2016 19:34

Amber G. wrote:^^^ Thank you. I am glad that this was helpful.

I am posting the PRL article, for those who might be interested but do not have access. An article in PRL generally has a 5 page limit but in this case they let if go and allowed more than 5 pages.
https://dl.dropboxusercontent.com/u/181 ... 281%29.pdf

Interesting paper. It answers some of the questions asked in my previous post (but not all

). Couple of additional questions:

1 It says that other detectors for gravitational waves were made from '60s upto mid-2000s. There is no indication of how successful they were (obviously they were not, because this paper is the first report of such a detection) but no mention is made of why they were un-successful. Any comment would be appreciated.

2. So gravity waves pass through all matter in space (evidenced by the fact that it reached earth), the question is one of signal attenuation. Given that it moved objects on earth, one could expect it did the same in other masses it passed through. One would expect that this will reduce the strength of the gravity wave signal. How did the authors account for this in their calculations seeing that there is no way they can know the quantity and nature of matter it passed through from the site of explosion to earth.

3. Another way to confirm the data (or atleast locate the source of the waves) would be to measure the difference in time of wave arrival at Hanford vs. Livingston. I dont know if this data was reported or somehow used, in the paper.

4. Also, the wave is three-dimensional (I would think), whereas the detectors are 2-dimensional. How would they account for this.

The amount of environmental noise and the approaches needed to isolate the system from their influence is fascinating. Much of this seems to be as much of engineering than physics

(not talking about the calculations for the black-hole merger).....wish I knew more about signal processing to understand the signal manipulation done in the paper.

Amber G. · Post by **Amber G.** » 13 Feb 2016 19:40

Let me answer (comment on) some of the questions asked here.

To understand one does need background in math (otherwise things like "curved space" etc really can't be grasped IMHO) but I will keep math simple. I will also stick to Einstein's (1916) theory (classical general relativity) where gravity is not quantized. To give perspective I will use apologies with EM radiation/waves and Earth/Sun orbit. Hope some find it useful and interesting...

SriKumar wrote:Some general questions on this topic:

1. Are these gravitational waves the same that which causes the force of gravity between masses? Or are these a different kind of gravity waves.

Rather than saying waves causes force of gravity, it is perhaps more accurate to say that (according to Einstein's theory) gravity "causes" apples to fall, earth to go around the sun and also gravitational waves.

The analogy may be electric (or magnetic ) "force" and we all learn about coulombs law.. how two electric charges will attract (or repel) each other and move. We all saw pieces of paper "falling" towards an charged comb. Even the atom was explained as electron "orbiting" the nucleus similar to earth orbiting sun.

If you take a electric charge and accelate it, "radiates" and EM waves are formed. If you take a large charge and rapidly move back and fro, in, say, a wire (antenna) you basically get a radio transmitter. These EM waves travels, in VACUUME, with the velocity = c (called speed of light).

Similarly if you take a heavy mass (30x solar mass in the case of recent detection) and move back and fro *very rapidly* (reaching up to velocities c/2 in the recent case), it will "radiate" gravity waves -- (strong enough to be detected by LIGO)

2. The principle for detection is (as I understand it) interference of light, producing dark patches if they interfere destructively, or a bright spot if they interfere constructively. The interference is caused by a difference in distance traversed by the 2 light beams. How is such a sensitive apparatus (which can detect displacements of 10e-18 m) not be vulnerable to vibrations from various sources e.g. from within earth's crust (vibrations from plate movements for example).

Yes the apparatus is amazingly sensitive yet it is very hard to separate 'true' event from other "vibrations" as you described. (I remember once some body telling how much it snowed overnight in Alps by the disturbance it caused miles away in an interferometer in a Physics lab in Geneva). One of the key point is right "frequency", and amplitude which matches. And yes, there is BIG statistical analysis. They are quite sure that its a real event though. (sigma > 5.1, put it another way the probability is that they are not seeing a false event is like 1 event in thousands of years or so)

3. Can this apparatus detect changes in gravitational forces due to, say, planets moving around the solar system over time as they revolve?

Let me give a perspective. The sun/earth system gravity wave radiates (total power) about 200 watts. This is 200 Jules in a second. Compare this to the total gravitational energy of the system (KE+PE) which if you calculate, is of the order of 10^36 joules. To measure any detectable difference the sensitivity of the LIGO has to increase by thousands of trillions fold

4. How do they calibrate an instrument like this i.e. what is a 'resting' state where it is deemed to be free of gravitational influences, or at least, in some sort of an equilibrium?

Read the paper (I linked before) for details. This has taken 40+ years since the idea of LIGO came. BTW the idea came from the MIT professor (in late 60's ?) who want to build something so that his students can "measure" and become more interested in physics -(MIT transferred his course of general relativity from physics department to Math).

SriKumar · Post by **SriKumar** » 13 Feb 2016 19:51

Got it. So the gravity waves are created NOT by the property of mass but by the act of the mass oscillating rapidly. Thanks for the explanations. I did read the paper, and that threw up more questions, they are above your post...

. I am still reading the paper....it is possible that some are answered (# 3 perhaps) but will pick it up tonight.

Amber G. · Post by **Amber G.** » 13 Feb 2016 20:24

UB, TSJ, et-al - Again hope this is useful..

UlanBatori wrote:
UB garu. I dont know if you are asking in jest or in seriousness. But gravity perturbations travel at the speed of light, since it carries information.
Asking out of ignorance. Then how are they able to measure the propagation through the inside of a star? Distance is large, but time is on the order of a second or 10, and can they measure that from so far away?

Also, if gravity is basically a wrinking of Space-Time due to mass concentration, then propagation is instantaneous, hain?

Gravity waves, just like EM waves, travel at the speed of light in vacuum. EM radiation (light) slows down if it interacts - eg pass through water, or air, or glass. EM interacts with matter so not only it slows down, it may not even pass through objects -- hence the invention of Burqa.

Gravity waves passes through virtually everything (we know) without slowing down, hence if we have telescopes using gravity waves we can see through neutron stars, black holes, burqas, planets etc. So that's exciting. We will be able to look back in time too -- in the beginning of the universe for certain amount of time, no EM radiation could pass through so at present we can't see that back in past but if we could use gravity waves we can peek through that early childhood of the universe.

The power of Gravity waves goes inversely as distance (not as square of distance like force) so effect from far away, still hard to detect, but better than if it fell as square of distance.

Yes, gravity is "wrinking of Space-Time" or positive space curvature -- at least they tell us that Einstein said so. Gravity waves are more like "ripples" of that wrinking which moves with the velocity c. For "wrinking" you need a mass, for "ripple" you need that mass accelerating -- causing those "wrinking" to move -- not unlike the EM waves which results if a charge accelate.

For "static" system, Einstein's space-time wrinking basically results into Newton's gravity. For example if you want to calculate orbit of earth you take the direction of force in the line joining earth-sun *current* position. (and NOT where earth-sun position was 8 minutes ago).

But if Sun suddenly goes away (as TSJ said), earth will not "know" it went away and keep orbiting for about 8 minutes in the old orbit.

BTW power consumed in the gravity waves (or gravitational "radiation") for earth-sun system is about 200 watts. Compare this with the EM radiation (which is results of all charged particles in sun - oscillating and producing photons et) is about 10^26 watts. Compare this to the gravitational energy of the system (about 10^36 joules). (So earth's orbit will decay due to this power loss but it will take more than a few times the age of universe to detect any change even with best of LIGOs)

TSJones · Post by **TSJones** » 13 Feb 2016 20:28

......just for discussion, if memory serves me correctly, the older a star is, the deeper the tone (vibration).......so young 'uns are tenors and sopranos and senior citizens are bass and altos.

habal · Post by **habal** » 13 Feb 2016 20:50

what exactly is 'gravity wave' ? Isn't it just another form of electromagnetic wave ?

Mort Walker · Post by **Mort Walker** » 13 Feb 2016 21:15

X-posted from Indo-US thread:

About the announcement from LIGO. The claim is a 5 sigma confidence, but I would want to confirm once data comes from LIGO-India as well. The last thing I want is a fiasco like the BICEP announcement back in 2014 with gravity waves in the CMB.

Amber G. · Post by **Amber G.** » 13 Feb 2016 21:17

habal wrote:what exactly is 'gravity wave' ? Isn't it just another form of electromagnetic wave ?

First: I don't think you mean "gravity wave".. recent all that excitement is about "gravitational waves"

Trust me if one used "gravity wave" instead of "gravitational wave" it will make any physicist *really* mad..

This is gravity wave: (see for example wiki link : https://en.wikipedia.org/wiki/Gravity_wave

And no, (in my opinion) it is NOT another form of EM wave. Like Maxwell formulated EM waves, Einstein predicted gravitational waves about 100 years ago. EM waves we use it all the time (when we "see" each other or listen to radio), it is only recently that we actually DIRECTLY detected gravitational waves. (in past there were many indirect experiments results so physicists were fairly sure of the theory).

Both graviton (particle - gravitational wave) or photon (EM waves) are massless. Gravitational force is MUCH weaker than EM force. Also as far as we know gravitons do not interact with matter like photons do, so the waves can pass through matter without slowing down.

Mort Walker · Post by **Mort Walker** » 13 Feb 2016 21:21

habal wrote:what exactly is 'gravity wave' ? Isn't it just another form of electromagnetic wave ?

A good question. Maybe Amberji can explain this.

From what little I understand, gravity has particle and wave like characteristics, but gravitons have zero mass and charge. The math is too mind boggling for a simpleton like myself where modern physics is merging quantum mechanics and general relativity.

Amber G. · Post by **Amber G.** » 13 Feb 2016 21:35

Mort Walker wrote:X-posted from Indo-US thread:

About the announcement from LIGO. The claim is a 5 sigma confidence, but I would want to confirm once data comes from LIGO-India as well. The last thing I want is a fiasco like the BICEP announcement back in 2014 with gravity waves in the CMB.

FWIW: We certainly hope that this news will accelerate the process and that building of the Indian leg of the detector-project get under way. (I don't know the current status, so some body correct me if I am wrong but the equipment project - Interferometer/detector part is sort of stuck in red tape since 2011).

(Recently I remember reading some place from some person that indeed there is some excitement in and things may move much faster)

This is why there is no data from LIGO india at present and we have to wait..but other existing places have confirmed it and this has been checked/rechecked since September. (Most important, as you know, is data analysis.. there are 1000+ authors of the paper and many Indian institutes/scientists have contributed)

As PRL paper say, sigma of 5.1 translates into the false alarm rate estimated to be less than 1 event per 203 000 years..

Amber G. · Post by **Amber G.** » 13 Feb 2016 22:41

SriKumar wrote: The amount of environmental noise and the approaches needed to isolate the system from their influence is fascinating. Much of this seems to be as much of engineering than physics ...

Wait till we get IT people get involved...
Sorry could not resist it..

Amber G. · Post by **Amber G.** » 13 Feb 2016 23:05

TSJones wrote:......just for discussion, if memory serves me correctly, the older a star is, the deeper the tone (vibration).......so young 'uns are tenors and sopranos and senior citizens are bass and altos.

For this event it is bass .. but judge it yourself:
https://youtu.be/QyDcTbR-kEA

UlanBatori · Post by **UlanBatori** » 13 Feb 2016 23:06

Wonderful.
So let's see if I get this. At Time T=0, there was a Big Bang. Space-time was concentrated at one point "until" then except there was no "until" before then.

So this Space-time expanded from that one point, and kept on expanding at some rate. All the mass (same as energy) that was concentrated in one point, was now found distributed all over this rapidly expanding Space.

It started concentrating further into little mass centers (little dips in Space-Time) that then started having more mass fall into these dips, and they called that Gravity.

As the mass fell in, it caused Radiation to go out, traveling at, what else? Speed of Light.

But I still get stumped on how an object far away from said center, across sheer vacuum, "feels" the presence of a dip in Space-Time far away. That would be gravitational attraction.

So I guess the Gravitational Waves travelled at the speed of light, and things sort-of equalized. Any changes in mass of mass centers, occur so slowly that you never feel it, you can't measure it.

Now these experts are saying that if the mass in a given dip changes HUGELY with time RAPIDLY, you should be able to sense the effect far away, with a frequency large enough that you can measure it. That could happen if two Black Holes went into a near-speed-of-light dance around each other.

But my question from our Department of Flying Broomsticks is, if gravitational attraction can fluctuate, can it oscillate so much that you can have negative attraction, IOW, repulsion, aka Anti-Gravity?

saip · Post by **saip** » 13 Feb 2016 23:06

We do have a Pakistani in this too (a Parsi, though). Nergis Mavalwala.

Link

member_22733 · Post by **member_22733** » 13 Feb 2016 23:12

Alcubierre drive uses "negative gravity" (in an indirect sort of way) to achieve warp bubble for faster than light travel mathematically consistent with general relativity.

https://en.wikipedia.org/wiki/Alcubierre_drive

member_22733 · Post by **member_22733** » 13 Feb 2016 23:15

Also Re Negative gravity:

A uniform distribution of mass/energy can cause space time to expand rapidly. This is how the universe is expanding due to the near uniform distribution of dark energy and matter.

TSJones · Post by **TSJones** » 13 Feb 2016 23:58

UlanBatori wrote:Wonderful.
So let's see if I get this. At Time T=0, there was a Big Bang. Space-time was concentrated at one point "until" then except there was no "until" before then.

So this Space-time expanded from that one point, and kept on expanding at some rate. All the mass (same as energy) that was concentrated in one point, was now found distributed all over this rapidly expanding Space.

It started concentrating further into little mass centers (little dips in Space-Time) that then started having more mass fall into these dips, and they called that Gravity.

As the mass fell in, it caused Radiation to go out, traveling at, what else? Speed of Light.

But I still get stumped on how an object far away from said center, across sheer vacuum, "feels" the presence of a dip in Space-Time far away. That would be gravitational attraction.

So I guess the Gravitational Waves travelled at the speed of light, and things sort-of equalized. Any changes in mass of mass centers, occur so slowly that you never feel it, you can't measure it.

Now these experts are saying that if the mass in a given dip changes HUGELY with time RAPIDLY, you should be able to sense the effect far away, with a frequency large enough that you can measure it. That could happen if two Black Holes went into a near-speed-of-light dance around each other.

But my question from our Department of Flying Broomsticks is, if gravitational attraction can fluctuate, can it oscillate so much that you can have negative attraction, IOW, repulsion, aka Anti-Gravity?

not to mess things up for the mongol, but more space time is being created every split second. oodles and caboodles of it....endlessly, and space time is full of energy......don't ask me how all of it is done, wish I knew because it bugs the heqq outta me.....

member_29325 · Post by **member_29325** » 14 Feb 2016 04:37

What is this "dark energy" -- is it energy contained in gravity waves, or "we don't know where all this mass/energy that we know exists has gone". My understanding is that it is the latter, but why can't it be "gravity wave energy", huh? Now I shall go back to lungi-squatting while smoking my beedi and watching passersby.

Bade · Post by **Bade** » 14 Feb 2016 14:59

Mort, Indian LIGO when installed and working ( say a decade considering INO is stuck or as good as dead too due to the glacial movement of Indian life) will improve the pointing accuracy even further to sources. So it is important to wrap up the lungi and get to work for the people at the funding agencies in Nai Dilli. If this does not light up their rears or their lungis, cannot say what will.

UlanBatori · Post by **UlanBatori** » 14 Feb 2016 16:47

Dark matter aka pakistan is what is needed to explain why Yooniverse is not expanding faster. Dark energy is what is needed to explain why Universe is not shrinking due to Dark Matter.
All pakistan. I still cannot figure out how ANYTHING can act across a vacuum - meaning total lack of anything. How can vacuum "oscillate" or "compress and expand" or "rotate polarization vector"?

The only NEWS here is, to quote one of dem EMMIETEE pissikists, it is time for NSF to decide on next big chunk of funding for their grand international LEGO/ champagne party, so they suddenly heard a WHUMP and THUMP from their UNG (utter nonsense generator) and their TGG (Total garbage generator) so they immediately declared that they have Observed Gravitational Waves.

Bade · Post by **Bade** » 14 Feb 2016 16:56

No one has yet unified all the forces of nature, well at least a working theory...that is all for visible (all of EM spectrum) matter....so the other non-visible (other than by gravitational pull) dark matter is a big unknown. If you want to learn more head to Santa Monica next week

where all the world's experts will discuss it at length...better weather too than in 99Fing temperature in Toomba !

Amber G. · Post by **Amber G.** » 14 Feb 2016 20:25

Bade wrote:Mort, Indian LIGO when installed and working ( say a decade considering INO is stuck or as good as dead too due to the glacial movement of Indian life) will improve the pointing accuracy even further to sources. So it is important to wrap up the lungi and get to work for the people at the funding agencies in Nai Dilli. If this does not light up their rears or their lungis, cannot say what will.

Bade, Mort and others, I hope so. NaMo not only congratulated the scientific community , but also said India would look to hosting a LIGO lab now. I no longer know much about Indian scene but I get good vibes, what kind of vibes do you get? TIA.

Amber G. · Post by **Amber G.** » 14 Feb 2016 20:28

UlanBatori wrote:Dark matter aka pakistan is what is needed to explain ..

But seriously, forget about other dark matters .. as I said in other dhaga..

This detection is the beginning of a new era. The field of gravitational wave astronomy is now a reality.

ramana · Post by **ramana** » 14 Feb 2016 21:32

AmberG, Can you elaborate on how it could start a new era?

Bade · Post by **Bade** » 14 Feb 2016 22:05

AmberG, I am sure you have heard about the work stoppage at the INO site in TN, which was approved by GoI just after the DAE Symposium at IIT-G in late 2014, where lot of scientists signed the petition to GoI to allow for a speedy approval. But alas we are still stuck following the approval. Similarly, LIGO-India has not even got a formal GoI approval as of now. People (younger folks) I met recently are worried at the slow pace of approvals. Site location maybe in MP most likely, no official word...Hope MP politics is more conducive to science unlike in TN.

What the current discovery does is it boosts all other planned efforts like the one by ESA to launch a LIGO like config with satellites in space, where the arm lengths of the interferometer can be longer and give even better sensitivity to far away sources. That is what is being referred to as a new era in GW astronomy and ability to see even further out. Surely space based ones, would not have site specific constraints like LIGO-India is facing...though satellites by nature have shorter lifetimes in orbit unlike earth based systems which can be improved upon with time easily.

member_29325 · Post by **member_29325** » 14 Feb 2016 22:06

Not a physicist or anything, but seems to me that these devices or more accurate versions of these LIGO measurement devices could be used to determine cataclysmic events in the universe, like galaxies or stars colliding, though there are other ways of doing this already. Can't see why this would be of interest outside of the physics community.

member_22733 · Post by **member_22733** » 14 Feb 2016 23:04

ThiruV,

Gravity waves can travel long distances without losing amplitude as fast as EM waves do. They can also pass though most obstructions since they do not interact with them strongly.

What that means is we can look further back in time, probably even before the era that created the cosmic microwave background.

Now we need some experiments to directly observe a graviton. That would be truly new physics since it would give an observational basis for quantum gravity.

TSJones · Post by **TSJones** » 15 Feb 2016 00:00

ramana wrote:AmberG, Can you elaborate on how it could start a new era?

In no way am I trying to insinuate that I have the level of knowledge that AmberG does, so this is just my own ill informed opinion:.....

.....there is a lot of the universe that we are unable to see or sense. Some theorize that our particular universe is infinite and it keeps going forever and we just can't sense that far.

LIGO is a tool that may potentially help us in this regard and therefore may provide some amazing breakthroughs. BTW, we have a tough time seeing through the other side of our galaxy.

member_29325 · Post by **member_29325** » 15 Feb 2016 00:22

LokeshC, agree that astronomical observations at greater distances are a reality with LIGO. If the next level is to build a device to assist in experiments on whether gravity is quantized, that is still esoteric at least for the medium term. Still a long way from all those floating supercarriers that SHIELD will be building in due course.

These gravity waves do lose strength over distance, so there is probably an upper limit to the distance that we can make observations with LIGO-like devices.

TSJones wrote: LIGO is a tool that may potentially help us in this regard and therefore may provide some amazing breakthroughs. BTW, we have a tough time seeing through the other side of our galaxy.

Breakthroughs in astronomy and astrophysics is a given -- question was whether there were any other potential side effects of this discovery.

vishvak · Post by **vishvak** » 15 Feb 2016 01:28

What that means is we can look further back in time, probably even before the era that created the cosmic microwave background.

But we live in a unique situation:
* The only observable universe has been perfectly symmetrical and therefore expanding as well, since forever.
* Earth is the only planet with life form.
* Once in a billion year collision of black holes is already observed within hundred years of prediction of gravitational waves, and million years after formation of planet Earth.

If probability of first point is << then second and second is << third, then there should be many planets with life and observing this and weaponize this but no one has done that, too, per observations.

In other words, probability of all these events have to be 1, practically speaking which is about intelligent design more than science. Just trying to discount evil genius hypothesis here.

By the way, how come gravitational waves travel through substances. Were they observed in the north hemisphere while the even occurred in the southern one.

member_29325 · Post by **member_29325** » 15 Feb 2016 02:37

* Earth is the only planet with life form.

That is not likely - the Drake Equations indicate the opposite. The problem really is that in a X billion year old universe, planets die in a fraction of that time from the time the first living cell comes into being to when all life dies out. Look at earth, do you really think life on this planet has any chance of surviving another million years, let let alone 100 million (give or take an order of magnitude) years which is an upper bound for the oceans to boil away and all life forms to disappear. Even if there are multiple planets that support life forms, the chances of two planets having species that are sane enough to survive and advance to the level of detecting each others presence across a 100 or million light years is slim. Does not mean earth is unique by a long shot.

TSJones · Post by **TSJones** » 15 Feb 2016 19:28

the thing is, Gabriela González, the head of one of the LIGO data analysis groups knew what to look for.

IOWs, she was deliberately looking for a clash of two black holes. I learned this on NPR.

she *knew* what the data event should look like from her understanding of the theory of relativity. that must have been an interesting calculation......

TSJones · Post by **TSJones** » 15 Feb 2016 19:39

ThiruV wrote:
* Earth is the only planet with life form.
That is not likely - the Drake Equations indicate the opposite. The problem really is that in a X billion year old universe, planets die in a fraction of that time from the time the first living cell comes into being to when all life dies out. Look at earth, do you really think life on this planet has any chance of surviving another million years, let let alone 100 million (give or take an order of magnitude) years which is an upper bound for the oceans to boil away and all life forms to disappear. Even if there are multiple planets that support life forms, the chances of two planets having species that are sane enough to survive and advance to the level of detecting each others presence across a 100 or million light years is slim. Does not mean earth is unique by a long shot.

in biology if a wolf is needed that is what is provided.....

in Australia a marsupial "wolf" developed. unfortunately, now extinct. the mammalian grey wolf still thrives however.

same for the american cheetah, developed from a separate line of cat than the African cheetah. the american cheetah is now extinct also.

so somewhere, somehow, in the universe there are prolly very similar life forms......with functionality provided as needed by mother nature.....

Amber G. · Post by **Amber G.** » 15 Feb 2016 22:24

Sorry for a long post..I am sure there are lot of other articles, here is my perspective -

ramana wrote:AmberG, Can you elaborate on how it could start a new era?

Many have compared this event to Galileo's first telescope which started the whole new era of observational astronomy. Telescopes became better, other frequency ranges were added like radio telescopes, or gamma ray telescopes. For the first time we discovered moons on other planets, other galaxies, red giants, neutron stars etc...

This is I believe, and many other people are saying, is a start of such an era (next 100-200 years).

Up till now, from radio telescopes to optical telescopes, in all the common factor is EM (Electromagnetic Waves). This has been the case up till now in virtually *all* of observations..

The historic similarity between this and discovery of EM waves is quite interesting..

Maxwell studied Electromagnetism forces mathematically and beautifully, perhaps the most famous physics equation ever (more famous than E=mc^2 to a physicist!), produced the mathematical foundation. And he, (just like Einstein did with gravitation), predicted existence of EM waves. The velocity of EM waves in vacuum, per his theory came out equal to c (velocity of light). This was an interesting coincidence, so he predicted light is nothing but EM wave.

Hertz discovered these waves, using his mastery of engineering instruments - to transmit and receive radio pulses using procedures that ruled out all other known wireless phenomena - very similar to this case. The frequency etc matched exactly what Maxwell's theory predicted, and what Hertz (we used hertz unit in his honor) started is now used everywhere. We can created EM waves easily, but at present, it is not easy to created Gravitational weaves (need massive black holes) so two way communication may not be practical but even one way is quite exciting.

I don't think I am overstating it but for physicists this is very exciting.

Up till now, in virtually 100% of cases all fast (velocity=c) type communications and observations have used one and only type of waves. Until now, the only fundamental waves we’d ever observed were EM - be it radio signals or light. Now we see other half of the sky, so to speak.

As some one said (approx quotes) -- It is like rewriting book of Genesis, replacing “Fiat Lux” with “Fiat Lux et Gravitatis Fluctus” ( Let There be Light and Gravitational Waves.). One of my favorite T-shirt (my son got it in MIT book-store), now needs a few more lines.

***

As a few have mentioned here, EM waves can not pass through, or get distorted. Now there is another avenue, Gravitational waves do not interact with matter that strongly so we can observe the part of universe which we could not have observed before. I am sure the new generations of LIGO will be more useful.

At present no one can see a practical way to produce a gravitational wave which is strong enough to be detected over distance, so at present or in near future we may still have to depend on cell-phone towers and such things

.

Amber G. · Post by **Amber G.** » 15 Feb 2016 22:52

TSJones wrote:the thing is, Gabriela González, the head of one of the LIGO data analysis groups knew what to look for.

IOWs, she was deliberately looking for a clash of two black holes. I learned this on NPR.

she *knew* what the data event should look like from her understanding of the theory of relativity. that must have been an interesting calculation......

TSJ - This is actually is the MAIN and the most important point. The "signal" was so small compared to all the other "noise" that it is mind boggling the amount of data analysis was able to confirm it with such a high confidence level. It is like my iPhone's is in the middle of Mumbai traffic ( where traffic noise and ever-continuing construction, loudspeakers, firecrackers, honking, can go over 100 decibels) and it's SIRI correctly interpreting my command whispered from a mile away because it's mic and software is trained to understand my voice.

Yes, I am exaggerating a little, the difficulty for the LIGO as compared to the above example is something like billion billion times harder.

***

For perspective, no one doubted that the gravitational waves existed. There were quite a few indirect evidences. This is the first time they were able to detect is directly but the basic concept of LIGO is something like 40 years. There was plenty of information about black-holes (from optical telescopes - indirect observation) and exact frequency and amplitude of such events..

Within minutes of the actual event, the "preliminary" analysis gave a heads up that there may be an interesting event..the data-analysis was "tuned" to just analyze the narrow range and look if there is such a blip which can match the theory at both the sites (within 10 ms of each other) ..it took them 3 months to check and recheck the data and the confidence level is pretty high (5+ sigma) that this blip was from a real event of black holes merging.

Amber G. · Post by **Amber G.** » 15 Feb 2016 23:36

Interesting tidbit - when EM waves were directly discovered by Hertz (in late 19th century)

Hertz did not realize the practical importance of his experiments. He stated that,

"It's of no use whatsoever .. this is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there."

Asked about the ramifications of his discoveries, Hertz replied,

"Nothing, I guess."

member_29325 · Post by **member_29325** » 16 Feb 2016 00:23

If Gravity waves don't interact with any matter because they are weak, and don't get degraded as a consequence, then maybe at some point, there will be some new discovery along the lines of "gravitational wave surfboard"-effect will allow harnessing these waves for some use. But I suppose the first step is to see how this fits in with the rest of EM theory.

member_29325 · Post by **member_29325** » 16 Feb 2016 01:10

TSJones wrote: so somewhere, somehow, in the universe there are prolly very similar life forms......with functionality provided as needed by mother nature.....

Just a hunch, but there is no reason why lifeforms have to be carbon-based or follow the same trajectory on earth, even if we assume the same laws of physics hold on all planets. Similarity may be at the cellular level or at the organism level...if there is one common thing about nature and science, especially physics, it is that nature has greater imagination than us puny humans.

UlanBatori · Post by **UlanBatori** » 16 Feb 2016 01:14

OK, I will then stake my claim to notoriety by declaring that

GRAVITATIONAL WAVES HAVE ABSOLUTELY NO PRACTICAL APPLICATION WHATSOEVER! NEVER!

There! Now everyone can quote me.

Seriously, can this be more significant than the discovery of the Pakistani Fedayeen soosai bummer sitting on Mars?
Also, sad to say, but I am not thrilled by NaMo's "Me Too!" declaration to build a LIGO lab in India. Why is that more important than, say, developing a jet engine? A decent hybrid car? A Dark Energy Lab? Isn't there any better use for Indian science R&D funds? Is this a good way to decide national research priorities?

Back to discussion. So if it takes a black-hole collision to even generate measurable gravitational waves, then I would say that the instrument/lab construction was based on an event probability far far far far less than that of winning the Ulan Bator Super PowerBall GigaJackpot. Obviously, having got someone to waste that kind of money, those operating it would be under more pressure than, say, those doing Cold Fusion research back around 1989. So I have to retain my healthy sense of

Sorry.

If this humongous event occurred, and as I hear it, "emitted more energy in a minute than there is light in all the Universe" , AND this wave travelled towards the LIGO Lab at the speed of light, why has **NOTHING** of it being observed in any other part of the spectrum? No supernova flash, no spinning, flashing quasar/pulsar/Stellar MASER/cosmic flash, no radio waves. They should have reached at the SAME TIME!!

Something smell fishy?

Sounds like more "Martian Meterorites" and "Water on The Moon" and "Life on Mars" budget-time hallucinations.

Vayutuvan · Post by **Vayutuvan** » 16 Feb 2016 02:22

TSJones wrote:
ThiruV wrote: That is not likely - the Drake Equations indicate the opposite. The problem really is that in a X billion year old universe, planets die in a fraction of that time from the time the first living cell comes into being to when all life dies out. Look at earth, do you really think life on this planet has any chance of surviving another million years, let let alone 100 million (give or take an order of magnitude) years which is an upper bound for the oceans to boil away and all life forms to disappear. Even if there are multiple planets that support life forms, the chances of two planets having species that are sane enough to survive and advance to the level of detecting each others presence across a 100 or million light years is slim. Does not mean earth is unique by a long shot.
in biology if a wolf is needed that is what is provided.....
...

C based life forms may not be only life forms. There could be other life forms too. I request people to read a book called "Dragon's Egg" by Robert L. Forward. That is hard SF and has nothing to do with Dragons of the as in books belonging to the genre of Fantasy. Here is the blurb for R L Forward from Wikipage

Robert Lull Forward (August 15, 1932 – September 21, 2002) was an American physicist and science fiction writer.[1] His literary work was noted for its scientific credibility and use of ideas developed from his career as an aerospace engineer.

But he is not an exobiologist. If anyone knows about an SF author who is also an exo-biologist, I would appreciate it if it is put into SF&F thread.