Physics Discussion Thread

The Technology & Economic Forum is a venue to discuss issues pertaining to Technological and Economic developments in India. We request members to kindly stay within the mandate of this forum and keep their exchanges of views, on a civilised level, however vehemently any disagreement may be felt. All feedback regarding forum usage may be sent to the moderators using the Feedback Form or by clicking the Report Post Icon in any objectionable post for proper action. Please note that the views expressed by the Members and Moderators on these discussion boards are that of the individuals only and do not reflect the official policy or view of the Bharat-Rakshak.com Website. Copyright Violation is strictly prohibited and may result in revocation of your posting rights - please read the FAQ for full details. Users must also abide by the Forum Guidelines at all times.
Amber G.
BRF Oldie
Posts: 6985
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 21 Feb 2016 10:19

vayu tuvan wrote:AmberG ji: please answer my question - onlee.

What is the question? (Sorry too much noise so I am not clear what is your question?)

member_29325
BRFite
Posts: 542
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby member_29325 » 21 Feb 2016 11:07

Hitachi electron microscope

Came across this while catching up...can't imagine what their counterintuitive conclusion was:

Whenever electrons are observed, they are always detected as individual particles. When accumulated, however, interference fringes are formed. Please recall that at any one instant there was at most one electron in the microscope. We have reached a conclusion which is far from what our common sense tells us.

member_22733
BRF Oldie
Posts: 3788
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby member_22733 » 21 Feb 2016 11:15

If you figure out the mystery behind double slit experiment, you have a Nobel prize waiting for you.

member_29325
BRFite
Posts: 542
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby member_29325 » 21 Feb 2016 11:58

LokeshC wrote:If you figure out the mystery behind double slit experiment, you have a Nobel prize waiting for you.


I believe those researchers already figured it out going by their last sentence.

member_22733
BRF Oldie
Posts: 3788
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby member_22733 » 21 Feb 2016 12:07

I think they are describing the mystery, which is that you get interference pattern even if you send one electon at a time. It interferes with itself.

johneeG
BRF Oldie
Posts: 3473
Joined: 01 Jun 2009 12:47

Re: Physics Thread.

Postby johneeG » 21 Feb 2016 12:17

LokeshC wrote:I think they are describing the mystery, which is that you get interference pattern even if you send one electon at a time. It interferes with itself.


Noob question: how do they release one electron only?

member_29325
BRFite
Posts: 542
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby member_29325 » 21 Feb 2016 12:19

LokeshC wrote:I think they are describing the mystery, which is that you get interference pattern even if you send one electon at a time. It interferes with itself.


But that sounds like the wave-particle duality conundrum which has been around for a while, though that was about photons.

UlanBatori
BRF Oldie
Posts: 14045
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby UlanBatori » 21 Feb 2016 16:00

Amber G. wrote:
vayu tuvan wrote:AmberG ji: please answer my question - onlee.

What is the question? (Sorry too much noise so I am not clear what is your question?)


Mostly due to all those kard-karod photon/electron collisions in the the "4000 year" claim based on the Journal of Wikipedia onlee.
1) What is the photon/particle interaction time?
2) Why should there be any interaction time, given that particle size <<<<< wavelength and so it is at best Rayleigh scattering, no change in frequency? AFAIK, a photon is not a micro-particle, it is a Heisenbergically uncertain packet of energy that is sweeping all over a given region of space.

That's also the "explanation" for why an electron also appears as a fringe: if you have the necessary time resolution, I expect that one may "observe" the trace of the electron will appear quite clearly at any instant, like an insect buzzing all over a given region. Of course, what r u going 2 use 2 observe that, is a different question. Another $10B experimental setup with Templates, (wo)manned by burger-munching grad students in Bavaria.

To help out with this 4000-year pakistan pit that the Physicists have dug for themselves, let me suggest that it has **NOTHING** to do with particle interactions, that is all so much nonsense from that Pissicks expert on Wikipedia. The 4000 years is consistent with the balance between gravity and light speed.


Theory-e-UlanBator On The Effect of Lahori Traffic on Light Attempting to Escape a Pakistan
Think about it. The current IkPatthari Fallacy (IPF) in its linearized form (Lorentz transform) suggests that gravity can pull light back, and in fact stop it at the g-level of the Event Horizon. Also, that a Sun-sized star could turn into a BH, maybe once Jupiter and Saturn and Uranus have been gulped down. So inside the Sun's core, the g-level must be already pretty high. So light will be considerably decelerated by gravity (don't ask me how, the yaks are working furiously on this in the stables of Ulan Bator on this deep question). But it is similar to what happens as you sit in seat 13F on an airplane as it takes off. First the engine noise is just loud, then it gets VERY loud as the plane accelerates to Mach 0.5 or so and the sound pattern changes, then it dies out quite a lot as Mach reaches 0.8 and the pattern sweeps mostly backwards.

This is the most likely explanation for the "4000 years". The net speed of light is very low near the center, then becomes higher as it comes more out. Most probably, DoPatthar ul Ulan Bator will publish a paper shortly on The Helical Trajectory of a Photon Leaving the Core of a Star.

The light may be moving tangentially at 300000000000 millimeters a second, but near the core, it is mostly around in a circle with only a tiny radial component. So I expect that INSIDE a Black Hole, it is incredibly bright, because all the trapped light is going round in circles.

P.S. Pls send NoBill Price to Ulan Batori, PO Box1313666, Gujranwala PO, Bakistan onlee.

A_Gupta
BRF Oldie
Posts: 11638
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 21 Feb 2016 19:06

1) What is the photon/particle interaction time?
2) Why should there be any interaction time, given that particle size <<<<< wavelength and so it is at best Rayleigh scattering, no change in frequency?


More wiki-science - radiative transport in the sun:
https://en.wikipedia.org/wiki/Radiation_zone

The nuclear fusion reactions in the sun :
https://en.wikipedia.org/wiki/Proton%E2 ... n_reaction

Note that the electron rest mass is around 0.5 MeV, so these gamma rays are not not much longer in wavelength than the particle size; also see Compton scattering:
https://en.wikipedia.org/wiki/Compton_scattering

UlanBatori
BRF Oldie
Posts: 14045
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby UlanBatori » 21 Feb 2016 19:23

Hmm! Those links are a gold mine, though for completely different reasons, THANKS! This "4000 years" sounds like a diluted version of the Carl-Saganesque "171,000 years".

Question I have is still whether one can get fairly swift warning of uber-cataclysms cooking at the core of the Sun. Of course I don't know what I would do with that warning, except maybe I don't have to worry about crawling on my hands and knees and mopping the floor of the crawl space clean. Or writing proposals beyond (well, the time when that reaches Earth).

Inverse Compton scattering is important in astrophysics. In X-ray astronomy, the accretion disc surrounding a black hole is presumed to produce a thermal spectrum. The lower energy photons produced from this spectrum are scattered to higher energies by relativistic electrons in the surrounding corona. This is surmised to cause the power law component in the X-ray spectra (0.2-10 keV) of accreting black holes.[clarification needed]{U can say that again}
Last edited by UlanBatori on 21 Feb 2016 19:29, edited 2 times in total.

A_Gupta
BRF Oldie
Posts: 11638
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 21 Feb 2016 19:23

A nice presentation on the structure of the Sun:
http://solar.physics.montana.edu/ypop/S ... cture.html

Amber G.
BRF Oldie
Posts: 6985
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 21 Feb 2016 22:08

Quoting some part of the conversation to keep the context
TSJones wrote:
Amber G. wrote: . . Do you know how long does it take for a photon from the center of our own sun to reach us on the earth..?

The answer is about 4000 years!

(it takes about 4000 years for it to reach from the center to the surface of the sun, and about 8 minutes afterwards. Graviton (irrespective of where it started) will reach in about 8 minutes.




go back and read LokescH message above. It is not photons that travel from the core tp the surface, but gamma rays.

wiki says thusly:

<snip>
.


TSJ, Lokesh, and others..there isn't really any difference between " a gamma ray" or a "photon"...
Physicists have long settled that particle vs wave property of light..

Don't tell it our brf Einsteins who are writing long posts after posts -- analyzing this duality (is it a wave? is it a particle?) .. or more absurd still, if this is the "same" or a "different" photon --poor souls -- they have no clue about any quantum phenomena yet think throwing insults at traditional scientists or wiki will somehow make them look smart)..

What I found rich was confusion between "pathan" and "photon" . and seemingly real confusion by the term "drunken walk" problem - as if it has anything to do with a drunk. :rotfl:

(Seriously - this 'drunken walk' problem is one of 3 major works (other two are relativity, and PE effect) of Einstein which could have won him a nobel. PE effect is the one which won him a Nobel)

Meanwhile the point why it takes a long time for a photon to travel from center of the sun to it;s surface.. what is the actual observable significance is lost.

Sorry that's all the time I have right now..

UlanBatori
BRF Oldie
Posts: 14045
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby UlanBatori » 21 Feb 2016 22:18

So, repeating the simple question for the 4th time: In your Wikipedia post on the drunken walk, what is the interaction time per interaction, to explain the calculation shown there? Just saying "photon interacts with 2.635734562 x 10^27 electrons, says nothing on why the speed changes from 3E-8 m/s. Interaction with one good mirror would have turned that photon right back into the face of the Sun's core, so transit time would be infinity.

If interaction time is zero then you have no explanation other than a lot of gratuitous pompous attempted insults - typically I see those coming from clueless politicians who are cornered and their hollowness exposed (like the one I cannot talk about), not from physicists. If it is non-zero, then let's hear what it is. On the other hand, if the Wikipedia analogy is garbage, then let's hear that.

From what I see, it sounds like the effect of an interaction is actually an energy loss (plausible) that then emits a new photon of different energy (lower frequency, longer wavelength). But how much per interaction? That will let us estimate whether the 4000 years or 171,000 years is closer.

If you have no clue, it's OK to say so.. I have no axe to grind here. Thanks!

But if the interactions with particles slow light down and shift it to lower frequency, then isn't the "red shift" observed in galaxies due to interaction with particles on the way, and nothing to do with Doppler shift? Or is there independent frequency measurement to say that it IS Doppler shift? Can you tell the difference? If you can't then the whole Hubble fallacy of expanding Universe comes crashing down.

Can we please have a more coherent answer than
Oooo! I am stunned by the ignorance of these posts
?? See "politicians" above..

A_Gupta
BRF Oldie
Posts: 11638
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 22 Feb 2016 03:12

UlanBatori wrote:So, repeating the simple question for the 4th time: In your Wikipedia post on the drunken walk, what is the interaction time per interaction, to explain the calculation shown there? Just saying "photon interacts with 2.635734562 x 10^27 electrons, says nothing on why the speed changes from 3E-8 m/s. Interaction with one good mirror would have turned that photon right back into the face of the Sun's core, so transit time would be infinity.


The photon's random walk through the Sun's core is worked out as a homework problem with solution here:
http://www.astro.wisc.edu/~townsend/res ... -10-28.pdf

member_22733
BRF Oldie
Posts: 3788
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby member_22733 » 22 Feb 2016 03:33

The key here is the word "SCATTERING", its absorbed and reflected off in a random direction, which usually makes a large part of the energy directed inward. This keeps going on and on until it reaches the surface.

BTW: AmberG, I am aware that photons range from gamma rays to low freq radio.

UlanBatori
BRF Oldie
Posts: 14045
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby UlanBatori » 22 Feb 2016 03:48

A_Gupta wrote:The photon's random walk through the Sun's core is worked out as a homework problem with solution here:
http://www.astro.wisc.edu/~townsend/res ... -10-28.pdf


Thx. I will wait for the Physicists to answer the question and explain to me the key assumption that changes the crow-fly distance to something so huge. And why that model is anywhere near relevant for photo (light) propagation. Sounds more relevant to gilli-danda or marbles.

A_Gupta
BRF Oldie
Posts: 11638
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 22 Feb 2016 04:00

Yours truly was a physicist. The Sun's interior is a dense plasma - i.e., a soup of charged particles that interacts readily with photons. As the homework solution points out initially, the mean free path of the photon in that environment is of the order of 10^-5 meters. Which means it propagates on the average that distance, before suffering a collision and shooting off in another random direction. It is essentially diffusing through the medium, like sugar in your unstirred coffee.

Hope that helps.

member_22733
BRF Oldie
Posts: 3788
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby member_22733 » 22 Feb 2016 05:05

UlanBatori wrote:
The light may be moving tangentially at 300000000000 millimeters a second, but near the core, it is mostly around in a circle with only a tiny radial component. So I expect that INSIDE a Black Hole, it is incredibly bright, because all the trapped light is going round in circles.

P.S. Pls send NoBill Price to Ulan Batori, PO Box1313666, Gujranwala PO, Bakistan onlee.



I am not sure what to make for the rest of your post save the bolded part above, because that phenomenon is true (in case of a stationary non-feeding blackhole):

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

However, that mechanism is not the one that is going on in the sun, because the center of the sun is much less dense, i.e. it does not bend the field around it enough to make the phemomena you mention to be the reason for the "4000" year thing.

I think you should look into statistical thermodynamics and how things "thermalize", I am sure you use that in hypersonic flying yak designs.

Everything "thermalizes" , i.e. reach a state of thermodynamic equillibrium with its environment following the laws of thermodynamics. And that includes such intense things such as the photons from CMB, here is a discussion:
https://www.physicsforums.com/threads/t ... ns.746609/

UlanBatori
BRF Oldie
Posts: 14045
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby UlanBatori » 22 Feb 2016 06:27

Sigh! Brings back nightmares of reading for the Yaqualifying exam. This random bouncing of photons just seems like a wrong explanation to me, though I have no sense of the density in the Sun's interior. 100 g/cc still does not sound like a truly dense enough medium to inhibit most of the light passing through. About 6 times that of uranium, and when uranium is really hot, I bet it looks somewhat translucent. The fact seems to be that the inner gamma rays zap the matter around them (get absorbed) and then those radiate.

Pls read the book where some terrist (imaginary of course) detonated a fusion precursor (gamma ray generator) in the stadium at Denver - excellent description of how the gamma rays vaporized everyone around the bum, and then those vapors glowed and radiated lower frequencies. So all this talk of the same gamma ray photon wandering drunk through the core of a fusion reaction is all so much imagination.
In gas dynamics laser lore, there is a thing called "small signal gain". it is the net between the absorption, spontaneous emission and the stimulated emission as a beam bounces off walls (total internal reflection) and traverses the same medium gazillions of times. I guess inside the Sun's core, the medium is far denser, so the absorption and spontaneous emission >> stimulated emission, and the photons cannot last very long. So think of the gamma ray photon as someone carrying Rs. 100,000 in currency notes trying to get through Central Park in NY. Not much will be left by the time s(he) escapes, if ever.

member_29228
BRFite -Trainee
Posts: 65
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby member_29228 » 22 Feb 2016 07:21

Dr. Signs on NPR says
" BH appear to be B because there is more light surrounding it, so it is lost in light"
TIFWEW

Also during my adolescent times my Guru through the holy book Modern Physics by DS Mathur
Said
In small packet
"Good absorbers are good radiators"
And said BB are good radiators

Looks like

For BH R = T = 0

Therefore anything discovered about it gets AA+ rating for a (BB )

Also small pooch

What happens to Van dear Waals equation in BH
Doe it hold
T must absolute zero
Volume will be zero
Only P will be infinite?
If there is no matter then how can P be perceived?


Chal better stick to strength of Materials rather than weakness of theory

TSJones
BRF Oldie
Posts: 3022
Joined: 14 Oct 1999 11:31

Re: Physics Thread.

Postby TSJones » 22 Feb 2016 09:33

delete
Last edited by TSJones on 22 Feb 2016 14:12, edited 1 time in total.

deejay
Forum Moderator
Posts: 3933
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby deejay » 22 Feb 2016 10:16

I am not sure I should be posting this here plus I might be interfering but unexplained noises heard by Apollo 10 crew have been declassified

https://www.rt.com/usa/333184-apollo-nasa-tapes-declassified/



Hope it is not a spoof.

A_Gupta
BRF Oldie
Posts: 11638
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 22 Feb 2016 16:30


johneeG
BRF Oldie
Posts: 3473
Joined: 01 Jun 2009 12:47

Re: Physics Thread.

Postby johneeG » 22 Feb 2016 21:53

Palmer wrote:Dr. Signs on NPR says
" BH appear to be B because there is more light surrounding it, so it is lost in light"
TIFWEW

Also during my adolescent times my Guru through the holy book Modern Physics by DS Mathur
Said
In small packet
"Good absorbers are good radiators"
And said BB are good radiators

Looks like

For BH R = T = 0

Therefore anything discovered about it gets AA+ rating for a (BB )

Also small pooch

What happens to Van dear Waals equation in BH
Doe it hold
T must absolute zero
Volume will be zero
Only P will be infinite?
If there is no matter then how can P be perceived?


Chal better stick to strength of Materials rather than weakness of theory


I think calculating pressure for black hole is not possible because according to Einstein gravity is a quality of Space-time. And the rest of the entities are called matter. So, I think there are no forces inside Black hole in Einstein system to calculate pressure.

Now, the interesting part is this: black hole is formed when the pressure inside a star increases to the extent where the star collapses under its own gravity. So, pressure should be infinite because that pressure is being caused by infinite gravity. If the pressure is infinite, then the forces acting inside the black hole would also be infinite. Normally, all scientists treat gravity as a force when they actually have to calculate something. So, Hawking also superposes Newton's system into Einstein's system and starts treating Gravity as a force. But, the interesting part is that according to Hawking, some radiation also escapes the Black hole even though nothing is supposed to escape. So, according to Hawking, forces are not infinite even though Black Hole is supposed to have formed because of infinite pressure(where star collapsed under its own gravity). That results in the theory Sphaghettification. If the forces are not infinite, then the gravity is not infinite. If the gravity is not infinite, then space-time is not infinite. That means no black hole. So, in short, Hawking is just changing the very definitions of Black Hole 180 deg. They keep contradicting themselves and then invent new theories to cover up their contradictions and nobody is supposed to point it out. If anyone points it out, they launch into a name-calling tirade.

Space-time = infinite(or undefined)
gravity = infinite(or undefined).
mass = finite.
volume = zero.
forces = infinite (or tidal forces according to Hawking) (or zero because gravity is not a force in Einstein system).
pressure = infinite because black hole was formed due to that (or zero because the gravity is not a force in Einstein system).
Temperature = directly proportional to pressure. So temperature is either zero or infinite depending on the pressure.

Just looking at the ridiculous figures, one can say that this is a silly theory. An object with zero volume but infinite gravity and finite mass. Infinite gravity means that it would attract everything and everything would already be inside black hole. And even then its not possible because a black hole has zero volume.

Yayavar
BRF Oldie
Posts: 4775
Joined: 06 Jun 2008 10:55

Re: Physics Thread.

Postby Yayavar » 22 Feb 2016 22:08

Amber G. wrote:
vayu tuvan wrote:I think the papers were already written and ready to go the moment they detect the signal. All they had to do was to plug in the signal strengths and other stats data and write up the conclusion(s) and off the papers go to Science/Nature/PRL etc.

Original signal was detected in September, and right away the preliminary calculations told them to take deeper look at data.... It took them months of checking and rechecking to reach the confidence level they reached. Meanwhile there were few more events detected .. good enough (less than 2-3% chance that it was false positive) but it was not broadcasted. ... but why let facts get in the way of conspiracy theories..


Why a conspiracy theory? It is a valid question. The first time round - the paper was about to be published and then stopped by revealing that it was a deliberately inserted false signal. Why let everyone do the extra work? What was the social reasoning? VT's explanation makes sense.

The question was not about the current paper (or its physics).

Vayutuvan
BRF Oldie
Posts: 10417
Joined: 20 Jun 2011 04:36

Re: Physics Thread.

Postby Vayutuvan » 22 Feb 2016 23:25

A_Gupta wrote:Equations for stellar interior:
https://en.wikipedia.org/wiki/Stellar_s ... _structure

Four linked first order DEs can be solved quite easily, no? Numerically I mean. But there seems to be lot of assumptions and simplifications while arriving at those equations. Have they simplified far too much (to channel Einstein)?

Vayutuvan
BRF Oldie
Posts: 10417
Joined: 20 Jun 2011 04:36

Re: Physics Thread.

Postby Vayutuvan » 22 Feb 2016 23:27

AmberG: Here ( viewtopic.php?p=1982517#p1982517 ) is the question I posed which yayavar posed again. Thanks.

Vayutuvan
BRF Oldie
Posts: 10417
Joined: 20 Jun 2011 04:36

Re: Physics Thread.

Postby Vayutuvan » 22 Feb 2016 23:31

johneeG: Your argument does not stand. You are assuming that the domain is continuous. It is not once it falls below a certain distance scale. For example spin is quantized.

Amber G.
BRF Oldie
Posts: 6985
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 22 Feb 2016 23:44

This is important so please read.
Folks - I started putting my perspective in this thread specially because of an explicit request from Ramana. I am a physicist, know what I talk about, and quite well known, and respected, to explain complex stuff in laymen's language.

In this respect I put an extremely educational post (https://forums.bharat-rakshak.com/viewtopic.php?p=1982381#p1982381 - please do read it again, it is a nice post) trying to explain, the "delay" between gamma ray flash and GW. The noise created by Ulanbator's (and a few of his admirers') in deluge of absurd posts (which, of course is their choice), made it hard to carry out any sensible discussion. Old habits die hard, so I still post, but I wonder if brf now is a place to carry out any technical discussion.

UB Professor ji, I thought even Gujranwala Institute of Technology has some integrity so I find it a little odd, if not dishonest, when you insinuate that "AmberG is claiming that interaction time for photo/proton or photon/electron is long". I said no such thing. It is fun to read all your (and your admirers) "scholarly" posts but please stop misquoting me. Also please let me know which "wikipedia" article I cited which you are referencing below" - I hope you just did not make that up.

UlanBatori wrote:
So where is the basis for claiming that A PHOTON takes 4000 years to travel from the Sun's center to the surface, please? Read it on Wikipedia? { No I did not read (or write) that Wiki article before I posted the post in brf}

AmberG is claiming that interaction time for photo/proton or photon/electron is long, { I did not}
And I don't understand why photon/electron interaction should take any time at all.

If interaction time is not long (and I don't see it mentioned at all in that Wikipedia example that AmberG cited) {can you please explicitly point out WHICH wiki example I am citing} then the transit time is **NOT** increased. Rajdhani express zips past 1,000 stations without slowing down. Station Master may wave green flag, but thats about it. Either way, the 4000 years is .... a bit like one of dem templates?

As for the utter lack of destructive power in a GW, bleaaah! Who cares then, hain? Half the fun is watching the buildings fall, as they say...

Some points, (with bolded text) all with due respect :mrgreen:
- My original reference to photon(s) in center of a star like Sun was not wiki. Yet wiki is not too bad.(In an MIT study of physics related stuff, they found Wiki was more accurate than most of the other news papers -even some of the best scientific papers). But still one needs to follow what is written in our ancient books:
यस्यनास्ति स्वयं प्रज्ञा, विकी :) ज्ञान तस्य करोति किम?
लोचनाभ्याम् विहीनस्य, दर्पणम् तस्य करोति किम? :-o

(Rough translation: Wiki knowledge is as useful to a person without common sense as a mirror to a blind 8) )

- Amber G has not said anything about photon/proton interaction. ( Neither I mentioned drunken pathans) I simply said what I said (please do read the original post, it is very clear).

- As to destructive power of GW (you and your admirers post about 27000 on Ritcher scale, and superman's planet breaking apart due to tidal force is still there) I am sure YOU do not care or understand, but for everyone elsewho can follow basic math may. (Read my posts again.For most of us, there is a difference between 10000000000000000 and 0.00000000001 even if some do not have a clue to care about it. /sigh/

*****

UB,

If you REALLY wanted to understand or discuss what is the significance of " 4000 years delays due to photon", you could have asked it in a way that I think you are interested in learning, and I would have been happy to discuss it.. after all who knows, we may share the same alma mater, you having advantage of being 10 years or so younger... it might just be conceivable that you may be sitting in one of my ( or somebody like me) physics lectures for Engineers... :P
Last edited by Amber G. on 23 Feb 2016 00:58, edited 1 time in total.

Amber G.
BRF Oldie
Posts: 6985
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 23 Feb 2016 00:02

vayu tuvan wrote:AmberG: Here ( viewtopic.php?p=1982517#p1982517 ) is the question I posed which yayavar posed again. Thanks.

I think it was obvious, I was adding to your post, not contradicting your post I am sure you would agree that it is a relief to learn that there are still a few people in brf who have courage to say:

I don't believe in earth being flat or moon having a giant rabbit

:)

Amber G.
BRF Oldie
Posts: 6985
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 23 Feb 2016 00:40

A_Gupta wrote:Yours truly was a physicist. The Sun's interior is a dense plasma - i.e., a soup of charged particles that interacts readily with photons. As the homework solution points out initially, the mean free path of the photon in that environment is of the order of 10^-5 meters. Which means it propagates on the average that distance, before suffering a collision and shooting off in another random direction. It is essentially diffusing through the medium, like sugar in your unstirred coffee.
.


A_Gupta, TSJ, LokeshC et al -
Nice analogy by A_Gupta..I have used similar examples to make students excited about physics I have seen even physicists who might not have heard it before become surprised till they do the calculation).

The molecular velocity in water (at ordinary temp) is very high.. so much so that if you drop a bottle of Rooh-af-za in New York and then catch a flight to Mumbai, there will, in theory, be some Rooh-af-za molecules will reach Mumbai before you do. Yes molecular velocities are that high.. but it takes much longer to "diffuse"..(At present there is NO experimental method sensitive enough to detect those one or two Rooh-af-za molecules. It will take MUCH longer time, even if those Roof-af-za had radio-active tracers, to detect them experimentally)

The photons in Sun are not molecules of Rooh-a-za but the model (random walk) used gives fairy sensible result (which can be measured). Retaionship is very much like diffusion speed and molecular velocity.

BTW, lot of this work, (Theory of Brownian Motion) could have won Nobel for Einstein. (As said before, he won for PE effect and not for Relativity or Brownian Motion)

****

Anyway the reason I introduced this example was just to explain the "time delay" of "photos" coming from (interior of) stars. Of course "random walk" etc are just "models" to solve a problem. Very similar to "Nuclear Shell Structure" (1963 Nobel) which explains structure of a nucleus. Or "Liquid drop Model" for nucleus. These model are just models - Atomic nuclei do not really have "shells" or made out of "liquid" but still these models are useful as they explain nuclear spectra.

My point there, was: (Explained in Layman's language):

- To study what happens on Sun's surface (solar flares, etc) we can observe photons (visible light or x-ray etc) but there is a time delay... so it takes us (on average) about 8 minutes before the information gets here. So the sun (surface) we see, is what it was 8 minutes ago.

- We also study interior of Sun (what kind of nuclear reactions take place inside etc). This information comes from studying photons (gamma rays etc -- it does not matter what we call) originated from interior of the Sun. (This is how we know, our sun is fusion reactor etc).
But at present, what we know is how Sun was some few hundred/thousands of years ago.

Now if some how, we can hear gravitons, (that is measure GW) the time delay will shorten to about 8 minutes even for interior of Sun.

This is the critical point in understanding. Not drunken pathans, or Bakistani bums or Rajadhani express.

Hope this helps.

Amber G.
BRF Oldie
Posts: 6985
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 23 Feb 2016 01:17

vayu tuvan wrote:
A_Gupta wrote:Equations for stellar interior:
https://en.wikipedia.org/wiki/Stellar_s ... _structure

Four linked first order DEs can be solved quite easily, no? Numerically I mean. But there seems to be lot of assumptions and simplifications while arriving at those equations. Have they simplified far too much (to channel Einstein)?


VT A small anecdote - Recently I was talking to a relative of CV Raman and we happened to talk about Kameshwar Wali's biography of Chandrasekhar. This is when I was told of this, and it was mentioned that NO book or article has mentioned this anecdote of CV Raman. CVR was extremely good in judging potential of young students.

A very young student showed his work to CVR (work about stellar structure but using very simple calculation involving Compton scattering to predict some important stuff). CVR was impressed and said"
"This person is genius, and going to be a great physicist"

The boy was his nephew and did turn out to be a great physicist. (1983 Nobel - Chandra). All his work about Stellar structure has been confirmed by experiments.

(The person who told me, (himself a very bright physicist) heard the story first hand from some one who was present when that conversation took place, was interviewed for Wali's book but the story did not make into Wali's book)

Amber G.
BRF Oldie
Posts: 6985
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 23 Feb 2016 01:22

deejay wrote:I am not sure I should be posting this here plus I might be interfering but unexplained noises heard by Apollo 10 crew have been declassified

https://www.rt.com/usa/333184-apollo-nasa-tapes-declassified/



Hope it is not a spoof.

FWIW, IMO it is a spoof but I guess many (at least in brf :P ) will fall for it.

UlanBatori
BRF Oldie
Posts: 14045
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby UlanBatori » 23 Feb 2016 03:00

Now if some how, we can hear gravitons, (that is measure GW) the time delay will shorten to about 8 minutes even for interior of Sun. This is the critical point in understanding. Not drunken pathans, or Bakistani bums or Rajadhani express.


NOW v r coming to grips with the central issue. If there is a huge event inside the Sun (otherwise why would there be measurable Gee-Dubyas even in theory?) then WILL it take 1,71,000 years for the info to reach the surface and cause massive flares/sunspots etc? Wouldn't the info propagate as a shock wave? I am too far gone after long travels across the Mongolian Steppe, to try finding my calculator to try figuring out the shock speed, but I am guessing it should be AT LEAST Mach 5 by earth standards, which is about 1.5km/s. The radius of the Sun is 696,000km? :shock: so let's say 750,000 to divide easily with my groggy brain, gives 500,000 seconds. That's around 100 hours. When that gets to the surface, even if all the gamma rays are wandering around drunk around the Dancing Dumbbells, the info has reached the surface, and a swift 8-minute flight to zap Pakistan (and everyone else - this is the Mother of All VBIEDs).

4000 years later, the remaining Chief Scientist of the Termites, the ruling species on Earth, will sagely shake her antennae and say:

AHA! I told you so! It was a Gravitational Event! Look at those broken Interferometer arms swinging in the 800-degree breeze!


So I have to ask again about the claim that Gee-Dubya holds the key to such crucial applications. Maybe something else, but certainly not this.

ramana
Forum Moderator
Posts: 54175
Joined: 01 Jan 1970 05:30

Re: Physics Thread.

Postby ramana » 23 Feb 2016 03:11

Folks stop the BENIS/Pingrej language.
I see no need for it.

So one more will lock this thread up.
Sorry for headmaster tone.

A_Gupta
BRF Oldie
Posts: 11638
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 23 Feb 2016 03:44

vayu tuvan wrote:
A_Gupta wrote:Equations for stellar interior:
https://en.wikipedia.org/wiki/Stellar_s ... _structure

Four linked first order DEs can be solved quite easily, no? Numerically I mean. But there seems to be lot of assumptions and simplifications while arriving at those equations. Have they simplified far too much (to channel Einstein)?


The four DEs in Wikipedia are certainly a first order apprroximation, if you search around there is a vast amount of research going on.

A_Gupta
BRF Oldie
Posts: 11638
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 23 Feb 2016 03:51

UlanBatori wrote:
Now if some how, we can hear gravitons, (that is measure GW) the time delay will shorten to about 8 minutes even for interior of Sun. This is the critical point in understanding. Not drunken pathans, or Bakistani bums or Rajadhani express.


NOW v r coming to grips with the central issue. If there is a huge event inside the Sun (otherwise why would there be measurable Gee-Dubyas even in theory?) then WILL it take 1,71,000 years for the info to reach the surface and cause massive flares/sunspots etc? Wouldn't the info propagate as a shock wave? I am too far gone after long travels across the Mongolian Steppe, to try finding my calculator to try figuring out the shock speed, but I am guessing it should be AT LEAST Mach 5 by earth standards, which is about 1.5km/s. The radius of the Sun is 696,000km? :shock: so let's say 750,000 to divide easily with my groggy brain, gives 500,000 seconds. That's around 100 hours. When that gets to the surface, even if all the gamma rays are wandering around drunk around the Dancing Dumbbells, the info has reached the surface, and a swift 8-minute flight to zap Pakistan (and everyone else - this is the Mother of All VBIEDs).

4000 years later, the remaining Chief Scientist of the Termites, the ruling species on Earth, will sagely shake her antennae and say:

AHA! I told you so! It was a Gravitational Event! Look at those broken Interferometer arms swinging in the 800-degree breeze!


So I have to ask again about the claim that Gee-Dubya holds the key to such crucial applications. Maybe something else, but certainly not this.


1. Solar neutrinos produced in fusion reactions should also be detectable with only the speed-of-light delay, as they also mostly sail through matter.

2. You are absolutely right that a large event in the core of the Sun will produce shock waves, etc., that will propagate much, much faster than diffusion. Diffusion is what is happening in a state of almost thermal equilibrium. A large event, almost by definition, is a huge deviation from equilibrium.

3. You are also right that it is very unlikely that gravitational waves will tell us anything about the interior of the Sun. But remember that tidal locking we talked about with regard to the moon? That is complicated because the moon and earth are made up of a variety of rocks, and iron cores and so on. But imagine two neutron stars in a tight orbit around each other. They are, we think, made up of homogenous neutronium; and we can detect gravitational waves from this orbiting pair. The poorly knowns are the equation of state of neutronium and tidal dissipation in neutronium; and maybe gravitational waves by giving us another handle on their orbits will enable us to deduce properties of neutronium; or discover internal structure of neutron stars, or something.

TSJones
BRF Oldie
Posts: 3022
Joined: 14 Oct 1999 11:31

Re: Physics Thread.

Postby TSJones » 23 Feb 2016 05:18

we receive info about stars from seismic waves created inside the star that makes them vibrate which is seen by the Kepler space scope which detects the vibration from the star's light.

what creates the seismic waves is the pounding of erupting material rising up and falling back down onto the star as well as the plasma moving about inside the star..

also double star systems work on each other as well and gives us a lot of seismic info.

this possibility of seismic info was was first suggested by a Danish astronomer after the vibrations were observed by the Kepler scope in its search for planets.....

Amber G.
BRF Oldie
Posts: 6985
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 23 Feb 2016 06:08

Good points..but just to add..
A_Gupta wrote:1. Solar neutrinos produced in fusion reactions should also be detectable with only the speed-of-light delay, as they also mostly sail through matter.

Yes, neutrinos travel near the speed of light, not exactly but there is more..I am not sure they will be too useful to cary the information about fusion reactions... Solar neutrino's (or neutrino's in general) are quite hard (VERY hard) to detect any way, and to learn anything from that (to know precise nuclear reaction(s) as one can study from gamma rays)is still harder. In fact, there was big discrepancy and confusion about even the predicted and measured flux of solar neutrinos. I will not go in details here but one can read more about it about this as 2015 Nobel Prize was related some explaining this (why no/few tau neutrinos were observed at Super-Kamiokande) -- For details see McDonald's work . I have mentioned this news in physics dhaga as that work (investigating neutrino oscillation) also got 2016 Breakthrough Prize in Fundamental Physics ($3 million - more money than a Nobel) (see for more detail mine or Bade's post https://forums.bharat-rakshak.com/viewtopic.php?p=1965935#p1965935

(Neutrinos are not massless like photon's and gravity effects them too .. but that is besides the point)

Special for brf jingo's - India is seriously interested in for both INO and LIGO. 8)

2. You are absolutely right that a large event in the core of the Sun will produce shock waves, etc., that will propagate much, much faster than diffusion. Diffusion is what is happening in a state of almost thermal equilibrium. A large event, almost by definition, is a huge deviation from equilibrium.


Again, not quite..most, if not all of our knowledge about nuclear reactions inside the Sun comes from those "photons". The significant point here is, 4000 years, in sun's life (>4 000,000,000 years), is something like a heartbeat. The delay in Sun's case really does not matter as precise nature of nuclear reaction is not changing that rapidly. I don't know what is a "large event" -- which can magically appear -- but some one exploding a suicide vest inside is not really likely :)

3. You are also right that it is very unlikely that gravitational waves will tell us anything about the interior of the Sun.


Actually this will another avenue to learn more and MOST likely tell us more about interior of stars.. specially neutron stars, black holes etc where EM radiation is just one side of the story.

Hope this helps.
Last edited by Amber G. on 23 Feb 2016 07:50, edited 2 times in total.

A_Gupta
BRF Oldie
Posts: 11638
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 23 Feb 2016 06:46

John J. Bahcall about Solar neutrinos:
http://www.sns.ias.edu/~jnb/Papers/Popu ... /paper.pdf

More is known about the Sun than about any other star and the calculations of neutrino emission from the solar interior can be done with relatively high precision. Solar neutrino experiments test in a direct and rigorous way the theories of nuclear energy generation in stellar interiors and of stellar evolution. These tests are independent of many of the uncertainties that complicate the comparison of the theory with observations of stellar surfaces. For example, convection and turbulence are important near stellar surfaces but unimportant in the solar interior. Hence, the solar neutrino discrepancy puzzled (and worried) astronomers who want to use neutrino observations to understand better how the Sun and other stars shine. Prior to June 2001 (see discussion of SNO experiment below), the solar neutrino problem seemed to most (but not all)
physicists to indicate that astronomers did not understand the details of the solar nuclear fusion reactions that produce neutrinos.




The SNO and Super-Kamiokande measurements together established two
extraordinarily important conclusions. 1) Physics not included in the standard model of particle physics occurs. Neutrinos change their type. 2) The neutrino measurements confirm the theoretical model of how the Sun shines. The measured flux of neutrinos from 8B {Boron 8} beta-decay, which depends approximately on the 25th power of the central temperature of the Sun, is in good agreement with the theoretical calculations. In short, the solar neutrino experiments showed that the standard model of particle physics is incomplete and the standard solar model is vindicated


Popular article from 2010: Neutrinos are a practical tool for astronomy (beyond the abstract, behind a paywall): http://www.scientificamerican.com/artic ... rino-eyes/

2. A moderately slowly moving low mass blackhole zipping through the Sun might be a large event. But barring stuff like that, nothing is going to produce a quadrupole mass moment large enough and moving violently enough to produce detectable gravitational waves.

3. "Actually this will another avenue to learn more and MOST likely tell us more about interior of stars.. specially neutron stars, black holes etc. "

Forgive me, I distinguish between the Sun on the one hand and neutron stars and black holes on the other; and non-binary stars from which you're not going to get detectable gravitational waves on the one hand and binary stars from which you might get gravitational waves on the other.

I also now see why people get irritated with our resident recognized and respected physicist. Nothing that I wrote was wrong, but was pedantically "corrected" anyway. Bye-bye from this thread!

PS: some fun stuff:
http://arxiv.org/abs/1511.08813
Order-of-magnitude physics of neutron stars
We use basic physics and simple mathematics accessible to advanced undergraduate students to estimate the main properties of neutron stars. We set the stage and introduce relevant concepts by discussing the properties of "everyday" matter on Earth, degenerate Fermi gases, white dwarfs, and scaling relations of stellar properties with polytropic equations of state. Then, we discuss various physical ingredients relevant for neutron stars and how they can be combined in order to obtain a couple of different simple estimates of their maximum mass, beyond which they would collapse, turning into black holes. Finally, we use the basic structural parameters of neutron stars to briefly discuss their rotational and electromagnetic properties.


PPS: Here is something very relevant to our previous discussion of the opacity of the sun's interior:
http://astrobites.org/2015/01/30/the-su ... iron-fist/

and an overview of the Standard Sun Model: http://www.ap.stmarys.ca/~guenther/evol ... s_ssm.html


Return to “Technology & Economic Forum”

Who is online

Users browsing this forum: Google [Bot] and 19 guests