Physics Discussion Thread

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Amber G.
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Re: Physics Discussion Thread

Postby Amber G. » 20 Aug 2018 20:37

^^^ Just to be clear;
- Space-time curvature is caused by any object with mass -- and one can easily measure the curvature caused by say our sun or earth. (That is how orbits of planets can be calculated accurately.(more accurately than Newton's method alone).
- Gravitational waves are *MUCH* harder to detect. One still needed LIGO to detect GW produced by colliding black holes (or neutron stars) and LIGO.

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Re: Physics Discussion Thread

Postby Neshant » 26 Aug 2018 06:08

Ligo is a fancier version of the Michaelson-Moresley interferometer first use to detect the constant speed of light back in the late 1800s. Basically it is an interferometer that if disrupted due to compression or expansion of space-time can be noticed.

But why is taking something the magnitude of massive black holes colliding to distort space-time. It must mean the fabric of space-time is really stiff. Something is needed to soften it up and then FTL travel becomes possible. The day that happens, it will be possible to travel to any solar system in the universe in an instant thereby opening up the whole universe for exploration.

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Re: Physics Discussion Thread

Postby Amber G. » 27 Aug 2018 02:57

Neshant wrote:Ligo is a fancier version of the Michaelson-Moresley interferometer first use to detect the constant speed of light back in the late 1800s. Basically it is an interferometer that if disrupted due to compression or expansion of space-time can be noticed.


Just a comment for perspective:

One of the most enjoyable experiment I did in my graduate level experimental physics was to "re-do" some of Michaelson's experiments using same/similar equipments and I really have a respect for precision it achieved.

But still those interferometers accuracy was of the order of wave-length (of a fraction of that) of light..about a few hundred nanometers)

For LIGO, the precision is about BILLION (Yes, a billion) times more! This is almost unbelievable. IOW if you take the distance between earth and Alpha Century (4+ light years).. it measures/detects the variation of the order of thickness of a hair.

Just think about that.

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Re: Physics Discussion Thread

Postby Amber G. » 27 Aug 2018 03:04

^^^ Also next step on LIGO is space based eLISA (planned for in 2030's) where each arm of LIGO will be 2.5 million Km in space. (This is compared to about 4Km on earth). -- Also in space it will not have problem like producing vacuum, or vibrations due to people (and cars) walking by ..

-- So we may achieve another factor of a million or 100 thousand.

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Re: Physics Discussion Thread

Postby SriKumar » 28 Aug 2018 04:30

Amber G. wrote:For LIGO, the precision is about BILLION (Yes, a billion) times more! This is almost unbelievable. IOW if you take the distance between earth and Alpha Century (4+ light years).. it measures/detects the variation of the order of thickness of a hair.=
Just think about that.
How are they able to isolate the LIGO from earth's vibrations (I know there's a 10 mile buffer zone or something like that) but at that level of precision, vibrations from earthquakes anywhere on earth and minor plate tectonic movements could affect its functioning?

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Re: Physics Discussion Thread

Postby Neshant » 29 Aug 2018 02:22

SriKumar wrote:
Amber G. wrote:For LIGO, the precision is about BILLION (Yes, a billion) times more! This is almost unbelievable. IOW if you take the distance between earth and Alpha Century (4+ light years).. it measures/detects the variation of the order of thickness of a hair.=
Just think about that.
How are they able to isolate the LIGO from earth's vibrations (I know there's a 10 mile buffer zone or something like that) but at that level of precision, vibrations from earthquakes anywhere on earth and minor plate tectonic movements could affect its functioning?


They have 2 ligos spread out geographically at different ends of the US (east and west) presumably on different plates.

The time at at which the ligo events occur have to be identical - which would not be so in an earthquake.

Second, the events are correlated in time with an event observed in space. I.e a bright flash, or burst of some electromagnetic energy. India's Astrosat space telescope played a role in that since it can see over a broad range at different spectral wavelengths.

Another ligo will be (or has been) built in Australia.

India too plans to build a ligo. US and Australia have proposed handing over the equipment and designs they used to build their ligos to India.

But India should build it's ligo on it's own to gain experience in engineering such projects rather than have turn key solutions handed over to it where we learn nothing. By having a different design than what a!ready exists, it will help ensure the findings are correct and maybe discover something more.

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Re: Physics Discussion Thread

Postby SriKumar » 30 Aug 2018 04:48

Neshant wrote:
SriKumar wrote:How are they able to isolate the LIGO from earth's vibrations (I know there's a 10 mile buffer zone or something like that) but at that level of precision, vibrations from earthquakes anywhere on earth and minor plate tectonic movements could affect its functioning?


They have 2 ligos spread out geographically at different ends of the US (east and west) presumably on different plates.

The time at at which the ligo events occur have to be identical - which would not be so in an earthquake.
A second (or third) LIGO is not going to help if each LIGO is not isolated well from even faint vibrations. Each LIGO instrument has to be absolutely isolated from any vibration given that they are so super-sensitive. An earthquake or other seismic events are going to affect each LIGO differently. Plates are elastic. https://www.ligo.caltech.edu/page/vibration-isolation

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Re: Physics Discussion Thread

Postby Amber G. » 30 Aug 2018 07:23

SriKumar wrote:
Amber G. wrote:For LIGO, the precision is about BILLION (Yes, a billion) times more! This is almost unbelievable. IOW if you take the distance between earth and Alpha Century (4+ light years).. it measures/detects the variation of the order of thickness of a hair.=
Just think about that.
How are they able to isolate the LIGO from earth's vibrations (I know there's a 10 mile buffer zone or something like that) but at that level of precision, vibrations from earthquakes anywhere on earth and minor plate tectonic movements could affect its functioning?

SriKumar - First VERY good question. For serious and worthwhile reply I will suggest do some technical reading - MIT/Caltech's LIGO has some very good article(s).. I have given references before and give some additional reference later.

But basically let me answer without going too-much technical..

First - The isolation techniques are many order of magnitude better than anything previously attempted. This is why LIGO has advanced other engineering processes. These include -
- Best vacuum (In 4Km tubes) possible.
- Best Thermal /vibration/seismic isolation..
ityadi ityadi ..


These truly are mind boggling.. Just for details see, for example:
From Caltech site: Vibration Isolation for LIGO Lab

There are many further advances .. for example Japan's KAGRA (Japan's LIGO lab) has all tubes buried under a mine in a mountain .. thus providing better temperature (super cold - so minimal thermal vibrations) and other controls. Of course eLISA will have everything floating in space - away from atmosphere and other vibrations..

We also know the "local" events effect nearby LIGO more than far away LIGO. Event like black hole merger will effect all the LIGO's.

BUT THIS ALONE IS NOT ENOUGH...

Still a person walking (or car driving far away) will produce much more disturbance than those colliding black-holes.
Lighting miles away -- sea waves on the shore .. (forget about millions of small earthquakes)..

Interesting anecdote - LIGO in Luisiana encountered interesting strange events -- turned out to be hunters using their guns in hunting season, far away, which scientists were not aware of before-hand.

To me what was specially surprising (in the sense that I did not think of it before the LIGO people pointed it out) that even the gravitation field variation due to objects (people, or air mass - cold air is heavier etc) moving caused the effect. (Think about it .. I have never came across any delicate apparatus where one has to take that into account. .

So how do they filter out the noise?
This is another miracle of computer scientists techniques.. (this is where lot of Indian scientists contributed)..
They have taken 'signature noise' of literally 100,000+ such events..(specially how they will effect two geographically separated LIGO's)
(** Yes, I was told that they did add signature for hunters hunting deer in Lousiana among one of those 100,000 library noises :) )

Very sophisticated computer programs filter out those noises.. and can detect black-hole mergers type signature wave pattern among all that noise..

Truly remarkable. ..

Thanks for a good question. Hope this was helpful.
Last edited by Amber G. on 30 Aug 2018 07:49, edited 1 time in total.

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Re: Physics Discussion Thread

Postby Amber G. » 30 Aug 2018 07:44

Few comments to add clear some issues:

Neshant wrote:

Second, the events are correlated in time with an event observed in space. I.e a bright flash, or burst of some electromagnetic energy. India's Astrosat space telescope played a role in that since it can see over a broad range at different spectral wavelengths.


Just to be clear, event like bright flash or EM waves was not observed before LIGO announced the results. In fact except for Neutron-star merger, previous events nothing was observed.

For NS event, it was LIGO which asked others to point their telescope at that direction.. and when corresponding EM waves were discovered it was all the better.


Another ligo will be (or has been) built in Australia.


Interestingly LIGO Australia (More advanced version of AIGO II (?) ) was fizzled out.. so INDIA got in.. it is LIGO India now which is going to open in 4-5 years. Kudos to Modi's govt to moving ahead so smoothly and fast. (There are advanced version planned now by China, Japan etc.. Australia has a older/smaller version and AFAIK there are no big plans to make it super.

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Re: Physics Discussion Thread

Postby Neshant » 30 Aug 2018 09:37

SriKumar wrote:
Neshant wrote:
They have 2 ligos spread out geographically at different ends of the US (east and west) presumably on different plates.

The time at at which the ligo events occur have to be identical - which would not be so in an earthquake.
A second (or third) LIGO is not going to help if each LIGO is not isolated well from even faint vibrations. Each LIGO instrument has to be absolutely isolated from any vibration given that they are so super-sensitive. An earthquake or other seismic events are going to affect each LIGO differently. Plates are elastic. https://www.ligo.caltech.edu/page/vibration-isolation



That's the whole point.
A ligo event is only considered valid if both ligos detect the exact same event at exactly the same time.
An earthquake going off at some point underneath the Earth does not propagate at the speed of light to all corners of the Earth. You'll first see a rumble in one ligo station and then the other spread out by quite a significant amount of time. That means it could not have been a real ligo event. Only if both ligos registered a hit at the same time presumably with the same pattern could it be a ligo event. By same time i mean a delay that would be roughly within the error range of the speed of light event. Also there might be filters for a specific bandwidth of frequency where they expect a ligo event to exist to narrow down the detection criteria using analog & dsp techniques.

The effect of other vibrations masking a ligo event however is a separate issue. Essentially the signal to noise ratio has to be maximized through various means in the design.

It should be possible for Indian physicists to build a crude ligo as a concept and expand from there on. Obviously there are many factors from thermal effects, humidity, electrical noise, RF, power supply noise, amplifier noise, drifts in performance of all kinds, capacitive and inductive kickback...etc to take into account. But the essence has to be a match up of results from Ligo at point A and another Ligo at point B.

They are probably wanting more ligos to be built around the world at spread out locations so they can triangulate the source of the gravitational disruption.

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Re: Physics Discussion Thread

Postby SriKumar » 30 Aug 2018 17:39

Neshant wrote:
SriKumar wrote: A second (or third) LIGO is not going to help if each LIGO is not isolated well from even faint vibrations. Each LIGO instrument has to be absolutely isolated from any vibration given that they are so super-sensitive. An earthquake or other seismic events are going to affect each LIGO differently. Plates are elastic. https://www.ligo.caltech.edu/page/vibration-isolation

That's the whole point.
I beg to differ, and this was my original question to Amber.G. Before we can talk about 2 instruments (LIGOs, barometers or thermometers) being accurate, we have to understand and ensure that each one of the instruments is accurate. Only when we have this, can we say that the readings of each instrument is valid; and only then can we compare readings from the two instruments and determine if they are recording the same phenomenon.

In other words, if the accuracy of one (or both) instruments is suspect, then we dont know what is being recorded.

The Caltech link I attached (later Amber G) discusses specifics in ample detail.

A ligo event is only considered valid if both ligos detect the exact same event at exactly the same time.

Agreed. However, as I mentioned before, my interest was to understand how one can ensure that each LIGO is reading things accurately. Only after we have that can we say that two LIGOs are giving an accurate reading of the same phenomenon (i.e. a gravitational wave passing through).

Amber.G- thanks for the post. I have more questions....which I will post later. Thanks.

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Re: Physics Discussion Thread

Postby Neshant » 31 Aug 2018 08:08

SriKumar wrote:In other words, if the accuracy of one (or both) instruments is suspect, then we dont know what is being recorded.


That's what I said right here :

Neshant wrote:The effect of other vibrations masking a ligo event however is a separate issue. Essentially the signal to noise ratio has to be maximized through various means in the design.

Obviously there are many factors from thermal effects, humidity, electrical noise, RF, power supply noise, amplifier noise, drifts in performance of all kinds, capacitive and inductive kickback...etc to take into account.

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Re: Physics Discussion Thread

Postby SriKumar » 31 Aug 2018 09:56

Neshant wrote:
SriKumar wrote:In other words, if the accuracy of one (or both) instruments is suspect, then we dont know what is being recorded.


That's what I said right here :

Neshant wrote:The effect of other vibrations masking a ligo event however is a separate issue. Essentially the signal to noise ratio has to be maximized through various means in the design.

Obviously there are many factors from thermal effects, humidity, electrical noise, RF, power supply noise, amplifier noise, drifts in performance of all kinds, capacitive and inductive kickback...etc to take into account.
Yes, I did read this. I guess you read the link I posted, which is good. :D

Note that it has been mentioned above as a 'separate issue', after implying earlier how two LIGOs somehow solve the problem of isolating vibrations in any one LIGO (2 LIGOs was also broached in your first response to my post about isolating vibrations from a LIGO). As far as I am concerned, ensuring accuracy of an instrument is not a 'separate issue', it is the core issue (like Kashmir is the core issue for Pakistan... :D ). BTW, I am still going through some of the literature at the MIT/Caltech website. The more I read, the more surprising it seems that it works at all.

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Re: Physics Discussion Thread

Postby Neshant » 31 Aug 2018 13:07

SriKumar wrote:
Note that it has been mentioned above as a 'separate issue', after implying earlier how two LIGOs somehow solve the problem of isolating vibrations in any one LIGO). .


Note your original question. You were talking about differentiating earth quakes from ligo events, not systemic instumental error. One of the reason 2 ligos are used is to solve the former. With 2 ligos, the diffenential reading between simultaneous events (when the signal is added together) is doubled while the differential between random events will tend to cancel out. That is one method which would be used to improve detection capabilities.

And so far I have not read any link as I don't yet have time.

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Re: Physics Discussion Thread

Postby SriKumar » 31 Aug 2018 16:43

Neshant wrote:
SriKumar wrote:
Note that it has been mentioned above as a 'separate issue', after implying earlier how two LIGOs somehow solve the problem of isolating vibrations in any one LIGO). .


Note your original question. You were talking about differentiating earth quakes from ligo events, not systemic instumental error. One of the reason 2 ligos are used is to solve the former. With 2 ligos, the diffenential reading between simultaneous events (when the signal is added together) is doubled while the differential between random events will tend to cancel out. That is one method which would be used to improve detection capabilities.

And so far I have not read any link as I don't yet have time.
The very first line in my post post is about isolating vibrations. That is pretty clear one would think. It was within this context that I brought up the matter of plate tectonics movements as a source of vibrations. Note my comment on the buffer zone was also within this context.

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Re: Physics Discussion Thread

Postby SriKumar » 31 Aug 2018 16:48

Neshant wrote:.And so far I have not read any link as I don't yet have time.
Well, I see you had time to read my posts, make posts here (and on other threads too) :D so, let me offer a few lines from the link I posted. The note below is more informative than any of my posts so far.

https://www.ligo.caltech.edu/page/vibration-isolation

Vibration Isolation
For an instrument that needs to remain as still as possible, it is ironic that LIGO is so sensitive that it can feel the smallest vibrations from near and far. LIGO is essentially a giant seismometer capable of sensing vibrations from traffic on nearby roads, weather patterns on the other side of the continent, staff biking alongside detector arms, ocean waves crashing on shores hundreds of miles away, and of course nearly every significant earthquake on the planet. Since gravitational waves will make themselves known through vibrations in LIGO's mirrors, the only way to make gravitational wave detection possible is to isolate LIGO's components from environmental vibrations to unprecedented levels. The change in distance between LIGO's mirrors (test masses) when a gravitational wave passes will be on the order of 10-19 m. To achieve this level of sensitivity, LIGO was constructed with multiple levels of active and passive vibration isolation systems. Many of LIGO's larger infrastructure systems that provide some additional levels of isolation are discussed in previous sections.

But LIGO's most sensitive components (its optics) required even more complex and highly specialized mechanisms for isolating them from even the smallest imaginable vibrations.

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Re: Physics Discussion Thread

Postby Amber G. » 31 Aug 2018 20:44

Another link which is good is from Caltech's lecture.. https://labcit.ligo.caltech.edu/~ajw/LIGO_SURF02_4.pdf

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Re: Physics Discussion Thread

Postby SriKumar » 01 Sep 2018 08:10

Amber G. wrote:Another link which is good is from Caltech's lecture.. https://labcit.ligo.caltech.edu/~ajw/LIGO_SURF02_4.pdf
Very interesting presentation. Wish I had known more physics (topics) to understand some of the slides. I see they used active seismic isolation.

What was used as an (absolute) frame of reference in this case for the vibration detectors- would the mirror ('test mass') itself be used as one? And it seems like they worked out the signals (waveforms) of gravitational waves from various sources ahead of time and searched for that signal.

What is the nature of the signal output from the LIGO photodetector- would it be the intensity of the light vs. time? I assume this is 'all' it would be since it is an interferometer. And I assume the seismic corrections applied to each LIGO would be different (i.e. the WA unit would have a separate set of corrections vs. the LA unit)?...because a single (Seismic or any other large) event would register differently on each LIGO and hence the (magnitude and frequency of) corrections would be different?

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Re: Physics Discussion Thread

Postby Amber G. » 02 Sep 2018 06:54

SriKumar wrote:
Amber G. wrote:Another link which is good is from Caltech's lecture.. https://labcit.ligo.caltech.edu/~ajw/LIGO_SURF02_4.pdf
Very interesting presentation. Wish I had known more physics (topics) to understand some of the slides. I see they used active seismic isolation.

What was used as an (absolute) frame of reference in this case for the vibration detectors- would the mirror ('test mass') itself be used as one? And it seems like they worked out the signals (waveforms) of gravitational waves from various sources ahead of time and searched for that signal.

What is the nature of the signal output from the LIGO photodetector- would it be the intensity of the light vs. time?
I assume this is 'all' it would be since it is an interferometer. And I assume the seismic corrections applied to each LIGO would be different (i.e. the WA unit would have a separate set of corrections vs. the LA unit)?...because a single (Seismic or any other large) event would register differently on each LIGO and hence the (magnitude and frequency of) corrections would be different?


If I am understanding you correctly..(If not I am sure you would have found the answer in the links you posted before)

The "output" is interference pattern.. light(intensity variation) along the small length. The point which boggles the mind, is that the delta-l (distance between two spots where you can tell the intensity is different. In classical interferometer, we notice dark and bright pattern. .. For example if delta-l is half a wavelength you see dark pattern.

(Some one claimed that LIGO is nothing more than old M&M's interferometer... this may be true in the sense if one assumes a rocket to moon is same as something which makes you climb one millimeter).

What is mind-boggling here is the delta-l for LIGO measured for gravitational waves (== the variation caused by the Gravitatioal wave between two mirrors) is about 10 trillionth of the wave-length of the light (which is used to produce the interference pattern!)

Weiss and party waited 40+ years for the instrument refinement.. Weiss's original LIGO paper (which he did not publish in journal but published only in MIT's internal paper) - in 1972 - had all these calculations etc..He did not published it then as there was no point unless there is some equipment to carry out the experiment.. I guess he can now publish that paper in journal. :)

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Re: Physics Discussion Thread

Postby SriKumar » 02 Sep 2018 19:19

Thanks for the clarifications. I was just trying to understand the time-varying aspect of the fringe pattern. The LIGO should be oscillating back and forth due to the gravitational wave, and this changes the fringe pattern as a function of time. Fringes are a essentially a spatial variation of light intensity in MM interferometry (from the little I know). Slide 44 in your link below suggests that some signal (brightness intensity?) was plotted as a function of time and not space (y-axis is not defined, x-axis is probably time). https://labcit.ligo.caltech.edu/~ajw/LIGO_SURF02_4.pdf

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Re: Physics Discussion Thread

Postby SriKumar » 02 Sep 2018 19:56

Is it possible to calibrate a more precise instrument (e.g.a LIGO) with a less precise instrument (e.g. vibration/seismic detectors). If you are aware of any specific literature on this process for LIGO, I am interested. The Caltech MIT link said that active control of the pendulum system is monitored and corrected (as needed) at about 16 megahertz.

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Re: Physics Discussion Thread

Postby gaurav.p » 08 Oct 2018 23:40

Graduate Student Solves Quantum Verification Problem
https://www.quantamagazine.org/graduate-student-solves-quantum-verification-problem-20181008/

Image

Some highlights of the article
- Urmila Mahadev spent eight years in graduate school solving one of the most basic questions in quantum computation: How do you know whether a quantum computer has done anything quantum at all?
- For a graduate student to achieve such a result as a solo effort is “pretty astounding,
- presented her protocol yesterday at the annual Symposium on Foundations of Computer Science, one of theoretical computer science’s biggest conferences, held this year in Paris. Her work has been awarded the meeting’s “best paper” and “best student paper” prizes, a rare honor for a theoretical computer scientist
- developed a way to use cryptography to get a quantum computer to build what we’ll call a “secret state” — one whose description is known to the classical verifier, but not to the quantum computer itself. It relies on what’s called a “trapdoor” function — one that is easy to carry out, but hard to reverse unless you possess a secret cryptographic key.
- I was never thinking of graduation, because my goal was never graduation.
- She figured out how to build the trapdoor functions at the core of the secret-state method by using a type of cryptography called Learning With Errors (LWE). LWE is widely regarded as a leading candidate for post-quantum cryptography, and it may soon be adopted by the National Institute of Standards and Technology as its new cryptographic standard, to replace the ones a quantum computer could break
- protocol is unlikely to be implemented in a real quantum computer in the immediate future. For the time being, the protocol requires too much computing power to be practical. It won’t be feasible within, say, the next five years, but “it is not completely off in fantasyland either,”.

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Re: Physics Discussion Thread

Postby Amber G. » 15 Oct 2018 22:21

Amber G. wrote:Prof Abhay Ashtekar - Inspiration to many.

Good Scientists Solve Problems, but Great Scientists Know What’s Worth Solving’
Image


Theoretical physicist Prof. Abhay Ashtekar is the recipient of this year’s prestigious Einstein Medal!

One more physicist we have talked about in Brf.

(He was also an inspiration, guru and friend to many of us - IIRC Bade and me mentioned him in brf long time ago. Congratulations.

Last time I mentioned it was when he became chair of LIGO/India's international advisory panel and was mentor to many of the people in LIGO team. I believe he is still at PennU.

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Re: Physics Discussion Thread

Postby Amber G. » 17 Oct 2018 10:31

This is one year anniversary of last LIGO discovery. What a year it has been. I am excited that that plans are developing rapidly for LIGO India - to be operating by the mid-2020s. Next steps towards a global network of "3rd generation" detectors. The exciting new field of Gravitational Wave astronomy has a very bright future!

Right now we are busy completing analysis of all the data from the second LIGO Observing Run, which ended on Aug 25 ( just after #GW170817). Has ay more Gravitational Waves have been found. Hope the answer will soon be given. Watch this space.

Meanwhile for Sri Kumar and others - this may be of interest:
A nice and comprehensive - even for nonspecialists is here:
https://www.ligo.org/science/Publication-GW170817BNS/index.php
And I think this may be able to answer many question you asked for the ligo design and how to isolated the equipment..
https://www.youtube.com/watch?v=6raomYII9P4&index=3&list=PLkrz6hkCfdHhK_B4b12_J4pm4o6EAkYCy

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Re: Physics Discussion Thread

Postby ArjunPandit » 17 Oct 2018 13:46

there was a statment from dont remember either michio kaku or neil degrasse tyson, that if scientists are celebrated like today's celebrities, human civilization will reach god like status

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Re: Physics Discussion Thread

Postby Amber G. » 17 Oct 2018 21:29

SriKumar wrote:Is it possible to calibrate a more precise instrument (e.g.a LIGO) with a less precise instrument (e.g. vibration/seismic detectors). If you are aware of any specific literature on this process for LIGO, I am interested. The Caltech MIT link said that active control of the pendulum system is monitored and corrected (as needed) at about 16 megahertz.

A good technical yet popular write up for calibration is in recent issue of LIGO ,magazine.. (see page 13) .
(I believe it does not require subscription, but if there is problem in access I can put link to my copy)
https://www.ligo.org/magazine/LIGO-magazine-issue13.pdf

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Re: Physics Discussion Thread

Postby Amber G. » 17 Oct 2018 23:11

ArjunPandit wrote:there was a statment from dont remember either michio kaku or neil degrasse tyson, that if scientists are celebrated like today's celebrities, human civilization will reach god like status

In my humble opinion - what I think will be nice if people learn science (and scientific principles/methods) rather than make scientists celebrities. Not the same thing. Worshiping your guru is useless *unless* one learns scientific principles.

BTW both Kaku and Tyson are no doubt celebrities but in my opinion incredibly poor scientists. Many of their statements are scientifically inaccurate (which made me cringe when I heard) and many more are misleading or sloppy. It is a shame that for many they are the face of "popular" scientists.

My favorite "celebrities" in physics word are people like Feynman, Landau, Gammow, Fermi, Bohr, Chandrasekhar - just to name a few - Not only first rate scientists but *very* good teachers. I really wonder sometimes why Tyson and Kaku type people are much sought after "experts" while we have *many* others who are available.

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Re: Physics Discussion Thread

Postby SriKumar » 18 Oct 2018 06:52

Amber G. wrote:
SriKumar wrote:Is it possible to calibrate a more precise instrument (e.g.a LIGO) with a less precise instrument (e.g. vibration/seismic detectors). If you are aware of any specific literature on this process for LIGO, I am interested. The Caltech MIT link said that active control of the pendulum system is monitored and corrected (as needed) at about 16 megahertz.

A good technical yet popular write up for calibration is in recent issue of LIGO ,magazine.. (see page 13) .
(I believe it does not require subscription, but if there is problem in access I can put link to my copy)
https://www.ligo.org/magazine/LIGO-magazine-issue13.pdf
The link works. Thanks.

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Re: Physics Discussion Thread

Postby ArjunPandit » 19 Oct 2018 16:10

Amber G. wrote:
ArjunPandit wrote:there was a statment from dont remember either michio kaku or neil degrasse tyson, that if scientists are celebrated like today's celebrities, human civilization will reach god like status

In my humble opinion - what I think will be nice if people learn science (and scientific principles/methods) rather than make scientists celebrities. Not the same thing. Worshiping your guru is useless *unless* one learns scientific principles.

BTW both Kaku and Tyson are no doubt celebrities but in my opinion incredibly poor scientists. Many of their statements are scientifically inaccurate (which made me cringe when I heard) and many more are misleading or sloppy. It is a shame that for many they are the face of "popular" scientists.

My favorite "celebrities" in physics word are people like Feynman, Landau, Gammow, Fermi, Bohr, Chandrasekhar - just to name a few - Not only first rate scientists but *very* good teachers. I really wonder sometimes why Tyson and Kaku type people are much sought after "experts" while we have *many* others who are available.


Completely agree with you on this. My maternal uncle attended some of lectures of Feynmann and was always in awe of it. However, it is not necessary a great researcher/scientist be a great teacher and vice versa. There have been too many generations where science is not cool and not for girls.
Coming back to MK/NDGT, true. At least MK still had some reasonable work on superstring theory to speak of. That said, we must not ignore the fact that they are still doing a service to science only. In our own traditions, not everyone will be a bhagirath or Krishna to bring new things to earth. Everyone has a role to play. Let's enjoy and take it FWIW

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Re: Physics Discussion Thread

Postby gaurav.p » 19 Oct 2018 17:23


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Re: Physics Discussion Thread

Postby Amber G. » 19 Oct 2018 23:29

Twinkle, twinkle little star, how I wonder what you are
.
Thanks to Subrahmanyan Chandrasekhar, we know! Today marks the 108th birthday of the first astrophysicist to win a Nobel Prize for his theory on the evolution of stars.

I am sure he would have been very happy to hear about recent discovery of Gravitational Waves and observation of coalescence of neutron stars!

(I distinctly remember when the news of Nobel for him was announced and I was happy that he finally received the well deserved recognition - I knew the family. His uncle also had a Nobel Prize in Physics. Many other people in his family were quite notable in sciences.

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Re: Physics Discussion Thread

Postby ArjunPandit » 20 Oct 2018 08:12

^^^sir you always make me learn. Didn't know cv Raman and s Chandrasekhar were related. Very Nobel family indeed.

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Re: Physics Discussion Thread

Postby Amber G. » 21 Oct 2018 05:03

ArjunPandit wrote:^^^.... Didn't know cv Raman and s Chandrasekhar were related. Very Nobel family indeed.

Yes, the family had *many* many world renowned personalities. Not only in Physics or sciences but in arts, medicine too. Many of his family members are/were very modest - for example a nephew was my classmate and very good friend, but no one in IIT (except very close friends) even knew that he was related to the family. (Our families have been close friends for 50+ years)

Let me just mention a few famous people in this family which many here may know but may not realize it (or may not even know this)

Chandrasekhara Venkata (C. V.) Raman (Noble Prize, Raman Effect)
Chandrasekhara Ramaswamy (brother of C. V. Raman) - famous meteorologist - (Ex) Director-General of the Indian Meteorological Department - Authority on Indian monsoonal patterns. (Very nice family - everyone in his family was very smart. (They were also very kind and fun loving for us kids). I learned a lot from him and his family - now second/third generation of the family - all at extremely good places)

Venkatraman Radhakrishnan (son of C. V. Raman) Astrophysicist(pulsars, interstellar clouds etc) .
Subrahmanyan Chandrasekhar (nephew of C. V. Raman - Nobel) Astrophysicist
Sivaraj Ramaseshan (nephew of C. V. Raman) Famous crystallographer (was Director of the Indian Institute of Science, President of the Indian Academy of Sciences etc.
Sivaramakrishna Chandrasekhar (nephew of C. V. Raman) Another famous physicist (liquid crystal technology - and since name was similar/ same as "chandra".. was many times confused with other nephew the astrophysicist.
Sivaramakrishna Pancharatnam (nephew of C. V. Raman) distinguished optical physicist (Pancharatnam phase for polarized beams passing through crystals was after this guy's name.
Chidambara Chandrasekaran (nephew of C. V. Raman) Famous demographer and biostatistician ( with Edwards Deming, he devised the Chandra-Deming formula) Big shot in Indian government/the World Bank and the United Nations- President of the International Union for the Scientific Study of Population
Ramaswamy Rajaram Another physicist (his wife is also a first rate physicist and their son too)

Of course, there are many in next generations - for example - V. Shanta (great-niece of C. V. Raman) a famous oncologist,
Uma Parameswaran (great-niece of C. V. Raman a Indo-Canadian author ( biographer of her great-uncle C. V. Raman.)

****
Another thing which impressed me was CV Raman (and his brothers/nephews/nieces) knowledge in other fields. CV Raman knew LOT about botany, Human eye (medical) etc.. I was amazed he will pick new stuff very fast.

From mother's side Shivaji Ganeshan (Tamil super film star) was close relative.. And some very famous Tamil authors.
***
Another incredible fact is some brilliant women in the family - Lalitha (Chandra's wife) was one of the first (if not the first) Indian woman - she was the only - one of very rare - woman grad-student of CV Raman. Lalitha comes from a very brilliant (and famous) family from her mother's side. (Chandra's love marriage was unusual in those days but this was a very brilliant couple and they had a very happy life)
(There is a biography by Wali which is very nicely written - If people want to read further about the family).

I could go on. I have very treasured memories and I am very happy and proud that some of the mine and their next generation people are good friends. :).

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Re: Physics Discussion Thread

Postby ArjunPandit » 22 Oct 2018 15:41

vijayk wrote:Glad I visited this dhaga and saw some real discussions:

I read in some string theory book that
1. There are possibly universes in other dimensions (multiverse) which we can't see just like dot trapped in 2-dimensional sheet can't access dot on 2nd parallel sheet.
2. We can't see these universes but feel effects of their gravity since gravity can cross dimensions
3. There are 10/11 dimensions according to string theory

Did this theory go anywhere

I had typed this answer from mobile but did not get posted somehow. Taking it here because my answer was not in pinglish and not for publishing in Scientific Mongol.
String theory still remains in theoretical domain and has not been proven yet. Apart from the fact that it provides a theory with graviton it does not provide anything that is testable NOW and could be tested anytime soon. It's biggest failure is to not say anything about dark matter and energy either.
2. I havent read its mathematics at all but what string theorists say is that even the approximate mathematics is very complex. Working out exact mathematics is still ahead in future. Unlike Einstein who had mathematics worked out by Riemann.

While UBji is venturing into the zone of weirdness, i prefer copying and pasting from wiki didi as I have not reached his levels of cosciousness. Why MOND is not the preferred string theory
1. It does not explain the formation of galactic clusters
2. It does not lead to a cosmological model
Jury is still not out. We are still awaiting next Einstein.

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Re: Physics Discussion Thread

Postby vijayk » 22 Oct 2018 23:51

Thanks Arjun! Very helpful

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Re: Physics Discussion Thread

Postby ArjunPandit » 23 Oct 2018 10:44

^^amber sir, amazing didn't know about it at all. Wow. I will copy and paste this on other social media

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Re: Physics Discussion Thread

Postby Amber G. » 24 Oct 2018 05:05

Happy to share an interview I enjoyed.

Prof Subir Sachdev was awarded the 2018 Dirac Medal in theoretical physics. CONGRATULATIONS !!

As many friends might know, he is alumnus of IIT, MIT and currently chair of Physics department in Harvard

I enjoyed this interview with Manju Shet . I hope you will enjoy it too.
https://www.youtube.com/watch?v=rtF8v66wT6c

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Re: Physics Discussion Thread

Postby Neshant » 29 Oct 2018 01:10

Image

A mezmerizing animation of a gravitational wave.

India needs to build the electronics and optics of the emitter and detector of it's own LIGO.
Merely having it handed from overseas does not do much to advance development which is the one of the major reasons for undertaking such a project.

------

If Light Contracts And Expands With Space, How Do We Detect Gravitational Waves?

https://www.forbes.com/sites/startswith ... 43916b19a5

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Re: Physics Discussion Thread

Postby Amber G. » 06 Nov 2018 22:05

I am particularly happy to see some of the scientists and friends of my generation are getting the recognition, including from Indian newspapers and GOI. Even BRF :) tolerates some serious posts not written in pingrezi and talking absurdities of MOND and what have you.

This year some of the most prestigious prizes have gone to our friends, gurus: (I have posted some of their work in Physics dhaga).
- Einstein Prize - Prof Abhay Ashtekar
- Dirac Medal - Prof Subir Sachdev (Harvard)
-New Horizon Prize - Prof Rana Adhikari (Caltech).

Rana Adhikari's one of the best presentation, if you are a serious student of physics and want to learn about gravitational waves and LIGO India is his lecture in Bangalaru. It is a 1 hour lecture but very enjoyable if you listen in full.

Einstein Lecture: Brightest Day Darkest Night

It may answer some of the questions raised by Sri-Kumar about how LIGO works.
Also it answers some of the questions about why we are giving importance (and money resources etc) to LIGO- India - what India's contribution is and what kind of technology we are developing. Nice lecture.

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Re: Physics Discussion Thread

Postby Amber G. » 10 Nov 2018 08:20

This is from from Rana Adhikari's social media which some of you may find interesting. He used his iPhone, wrapped it in clothes and put it on a bean bag (aka seismically isolating) and using iphone's accelerometer recorded the vibrations (1 minute long , second diagram is frequency distribution)
Image


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