Physics Discussion Thread

UlanBatori · Post by **UlanBatori** » 20 Feb 2016 16:41

Raja Bose wrote:Ah the hand waving (did I say wave? ) is in phultu flow....narayan narayan.....

Et tu, Bosee? And that was the unkindest cut of all.(I have been watching the Timeless Cleopatra(Late E.Taylor)Begum

on METV). There's Gravitational Wave 4 u - when she walks around, all men within 150 meters turn their heads like a Tidally Distorted Moon turning with the Earth.

And there come the Bystanders with the stones! How Galil-e-0, Pythagoras (is that a combo of a python and an Agora aka billi?) and So-cret(in)es and Arch-e-medes lived as long they did, is truly the Great Mystery.

Unlike supersonic flow, the physicists have no valid theory for superlumic propagation, or they would see that there HAVE to be finite limits for everything inside a BH. Their present theories hit the Light Barrier at (what else?) The Event Horizon (lumic equivalent of Mach 1). Until they get away from this BooBoo-e-EkPatthar, they will throw stones at all who question this modern equivalent of the Edge of the Flat Earth. When they come out with valid models and evidence for superlumics I may start agreeing that they are capable of thinking beyond their long strings of unprintable symbols (isn't that String Theory, hain?)

As for the differences between a vortex in a pressure field (what pressure field? vortices can occur in any fluid if there is a sink, pressure field or not, though it certainly helps to have a pressure field) isn't it all in the mind of the observer? As the song "Goodnight Mrs. Robinson" says - or was it "Fifty Ways to Leave Ur Lover"?

Can galaxies not exist, without someone transforming coordinates in some office in an Ivory Tower, hain? What about all those pictures taken by the NASA photographer of the Raasta-e-DUdh holding his camera high about the Galactic Disk? This is the problem that my yakherd-trainer kept telling us, as PIGS:

Nature is not "governed" by equations. Nature does not "obey" equations. Equations are weak attempts to describe Nature while seeing only a tiny, tiny part of it (and seeing it wrong).

So this:

U cannot understand unless U understand the Math

is Non-Arrogant. Non-Pompous. And Non-Pakistan?

member_29325 · Post by **member_29325** » 20 Feb 2016 19:24

UlanBatori · Post by **UlanBatori** » 20 Feb 2016 19:58

I find this notion of the 4000-year Voyage Of Da Photon very interesting. Has anyone identified specific photons as being 4000 years and 8 minutes old as they reached Earth? Is it possible to tell from their energy level (they must be EXHAUSTED, the poor things!) Are they then very red? Infrared?

Doesn't this also mean that we have no clue as to what may have happened inside the Sun, even 1 year ago? Maybe they have had a regime change? Maybe two dumbbells have developed in the Sun's Belly, named Rah-Ul and Abd-Ul? Maybe they are spinning around? Maybe they are going to marry any moment now, with the appropriate belly dance rhythm speeding up in frequency and amplitude?? Maybe the Mother of All Gee-Dubyas is going to come out of there any moment now, taking only 8.1 minutes to reach us?

Thanks a lot! I had insomnia as it was from reading Syria news...

member_29325 · Post by **member_29325** » 20 Feb 2016 20:11

UlanBatori wrote: Doesn't this also mean that we have no clue as to what may have happened inside the Sun, even 1 year ago? Maybe they have had a regime change?

What do you think solar flares are, huh?

Simply put, it is an explosive revolution caused by oppression and suppression into the core of one groups of photons -- at some point, the oppressed photons rise up and overthrow other photons in a glorious infrared/red revolution.

TSJones · Post by **TSJones** » 20 Feb 2016 20:22

I knew the speed of light can be variable depending on the material it is passing through but I had no idea about this:

here's whut NASA says.......

http://image.gsfc.nasa.gov/poetry/ask/a11354.html

According to the famous 'drunkard's walk' problem, the distance a drunk, making random left and right turns, gets from the lamp post is his typical step size times the square root of the number of steps he takes. For the sun, we know how far we want to go to get out....696,000 kilometers, we just need to know how far a photon travels between emission and absorption, and how long this step takes. This requires a bit of physics!

The interior of the sun is a seathing plasma with a central density of over 100 grams/cc. The atoms, mostly hydrogen, are fully stripped of electrons so that the particle density is 10^26 protons per cubic centimeter. That means that the typical distance between protons or electrons is about (10^26)^1/3 = 2 x 10^-9 centimeters. The actual 'mean free path' for radiation is closer to 1 centimeter after electromagnetic effects are included. Light travels this distance in about 3 x 10^-11 seconds. Very approximately, this means that to travel the radius of the Sun, a photon will have to take (696,000 kilometers/1 centimeter)^2 = 5 x 10^21 steps. This will take, 5x10^21 x 3 x10^-11 = 1.5 x 10^11 seconds or since there are 3.1 x 10^7 seconds in a year, you get about 4,000 years. Some textbooks refer to 'hundreds of thousands of years' or even 'several million years' depending on what is assumed for the mean free patch. Also, the interior of the sun is not at constant density so that the steps taken in the outer half of the sun are much larger than in the deep interior where the densities are highest. Note that if you estimate a value for the mean free path that is a factor of three smaller than 1 centimeter, the time increases a factor of 10!

Typical uncertainties based on 'order of magnitude' estimation can lead to travel times 100 times longer or more. Most astronomers are not too interested in this number and forgo trying to pin it down exactly because it does not impact any phenomena we measure with the exception of the properties of the core region right now. These estimates show that the emission of light at the surface can lag the production of light at the core by up to 1 million years.

The point of all this is that it takes a LONG time for light to leave the sun's interior!!

Vayutuvan · Post by **Vayutuvan** » 20 Feb 2016 21:02

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.
... but why let facts get in the way of conspiracy theories..

AmberG ji: How did you produce a CT out of that post? As you know most papers overlap in content. Most of the paper would have been ready even before September. Please give me a break. I bow to you in your Cosmology/HEP knowledge etc. but this is a little too much. While I am at it let me add that I don't believe in earth being flat or moon having a giant rabbit (statue).

Amber G. · Post by **Amber G.** » 20 Feb 2016 21:04

UBji - I was not "allowing" but "encouraging" to carry on...and I see that you have

. I may not have enough time to read and grok all those gems but allow me to just document here one case for the innocents..

The madrasa math is so bizarre, yet no one has corrected/commented on it so just let me do it.
I could have picked 1 out of 87 such items I have seen in the last few pages, but let me just choose one because I referred to it.

UlanBatori wrote:Related pooch that I have: This GW-quake must have ABSOLUTELY shattered things in its general vicinity. I mean, if you were 0.1 light year away, your world would have been torn apart by it. Like an earthquake of magnitude 270 on the Richter Scale. Or 2700. or 270000. Unimaginable.

Wouldn't THOSE have , radiating all sorts of flashes and blinks?

ThiruV wrote:At 0.1 light years away, the earthquake would probably be accompanied by X-ray and gamma ray emissions of fatal proportions and wipe out all life as everything is ripped apart, just like how it was before baby superman was put into a spaceship and sent to Kansas by Richard burton.

Madrasa math at its best!!!

Instead of just throwing number like 270,..270000 why not actually calculate . (Hint: Math is easy , specially if anyone paid smallest attention to a post posted here -- it has been all but done

). So please do the calculation now before you read on.. it ought not to take more than a few seconds to get into right ball park.

And Thiruji - I have seen the movie superman so I wasn't commenting on "joke" ..sheesh.. I was just saying that I was stunned to see some one, with even the most basic understanding of Physics will think something like that an atom is billion times BIGGER than the size of the earth. (and then think the problem is my lack of sense of humor /sheesh/...

Have you finished your calculations? Let me just dot the t's and cross the i's, so to speak..

The effect of tidal force (due to gravitational waves by the event at 0.1 light years) will be less than a human body being squished/ (or stretched) by the width of a human hair.
(An ordinary comb will have more effect due to static electricity)

(Folks - it will not be wrong to say that the LIGO experiment is nothing but seeing the stress created in a 4 km L shaped body with heavy mirrors -- the effect is exactly like a tidal force -- the amplitude due to event at 0.1 LY will be 10^(-8)m (instead of 10^(-18)m)

What about the tidal force due to gravity (like moon causes tides), if the large BHs were 0.1 light years? (Again the answer about 25 billion times smaller than that of the our moon.
(Don't believe me, just do your own calculation -- after all it is freshman Newtonian physics.

How about gravitational force (measured by effect on earth's orbit): Again do the calculation..about a million times less than Sun's force which keeps earth in the orbit.

(I happened to put a post before, where I imagined the distance of 1 LY and did say that other than asteroids in Oort cloud which will be much near to the BHs, there would be little direct effect on earth)

(Moral: Unlike EM, Gravitational waves can pass through most planets without any getting too much weaker - they do not heat up things (NO TANDOOR as UB's was imagining).. NO tearing up things like super man movies..this is precisely they are so hard to detect)
To understand this, all you need is to take madarasa math with grain of salt and NOT the scientists who actually make sense.
****

May be I will now take a break.. and sit back and enjoy the gaaliyan thrown at traditional science. (I don't expect the usual suspects to retract/edit their posts... madasa mathwala's never do such thing).

Amber G. · Post by **Amber G.** » 20 Feb 2016 21:09

TSJones wrote:I knew the speed of light can be variable depending on the material it is passing through but I had no idea about this:

here's whut NASA says.......

http://image.gsfc.nasa.gov/poetry/ask/a11354.html

According to the famous 'drunkard's walk' problem, the distance a drunk, making random left and right turns, gets from the lamp post is his typical step size times the square root of the number of steps he takes. For the sun, we know how far we want to go to get out....696,000 kilometers, we just need to know how far a photon travels between emission and absorption, and how long this step takes. This requires a bit of physics!

The interior of the sun is a seathing plasma with a central density of over 100 grams/cc. The atoms, mostly hydrogen, are fully stripped of electrons so that the particle density is 10^26 protons per cubic centimeter. That means that the typical distance between protons or electrons is about (10^26)^1/3 = 2 x 10^-9 centimeters. The actual 'mean free path' for radiation is closer to 1 centimeter after electromagnetic effects are included. Light travels this distance in about 3 x 10^-11 seconds. Very approximately, this means that to travel the radius of the Sun, a photon will have to take (696,000 kilometers/1 centimeter)^2 = 5 x 10^21 steps. This will take, 5x10^21 x 3 x10^-11 = 1.5 x 10^11 seconds or since there are 3.1 x 10^7 seconds in a year, you get about 4,000 years. Some textbooks refer to 'hundreds of thousands of years' or even 'several million years' depending on what is assumed for the mean free patch. Also, the interior of the sun is not at constant density so that the steps taken in the outer half of the sun are much larger than in the deep interior where the densities are highest. Note that if you estimate a value for the mean free path that is a factor of three smaller than 1 centimeter, the time increases a factor of 10!

Typical uncertainties based on 'order of magnitude' estimation can lead to travel times 100 times longer or more. Most astronomers are not too interested in this number and forgo trying to pin it down exactly because it does not impact any phenomena we measure with the exception of the properties of the core region right now. These estimates show that the emission of light at the surface can lag the production of light at the core by up to 1 million years.

The point of all this is that it takes a LONG time for light to leave the sun's interior!!

Yes TSJ'ji... I am glad that you did some checking..the 4000 year wasn't pulled out of hat (some people can actually do some math..)..Light from BH takes forever! This is why we are very excited that we have one other way to observe the universe.

member_29325 · Post by **member_29325** » 20 Feb 2016 21:10

AmberG wrote: And Thiruji - I have seen the movie superman so I wasn't commenting on "joke" ..sheesh.. I was just saying that I was stunned to see some one, with even the most basic understanding of Physics will think that an atom is billion times BIGGER than the size of the earth. (and then think the problem is my lack of sense of humor /sheesh/...

What is wrong with you? When did I write any of that? You seem to be a little slow on the uptake when it comes to jokes, but that's okay and not a crime. Pretending that you understand the joke and then analyzing the joke for scientific accuracy is pretty silly, unless you are on some sort of a measuring contest here. Half these posts are not entirely serious, esp. UB's, and you don't have to be a master in physics to comprehend that.

Amber G. · Post by **Amber G.** » 20 Feb 2016 21:40

^^^ThiruV - I confess "What's wrong with you" type comment was not I was expecting. (I thought you will be find something valuable in my post)

My singular point was to point out that the tidal force due to a BH type event will NOT (in any stretch of imagination) would cause the type of damage you though it would cause.

It seems that you have missed the whole point by a light year; so sorry if that is the case, and if I hurt your feelings sorry again . .. Ignore my posts if you think they are not valuable to you.

Over and out.

member_29325 · Post by **member_29325** » 20 Feb 2016 22:12

AmberG. wrote: ^^^ThiruV - I confess "What's wrong with you" type comment was not I was expecting. (I thought you will be find something valuable in my post)
My singular point was to point out that the tidal force due to a BH type event will NOT (in any stretch of imagination) would cause the type of damage you though it would cause.

I thought you were mocking that post all over again. But you seem to insist my post was serious, so be it. This is not about my feelings -- always the willing student, and you and others provide lots of good material. I have written other posts here that are factually and scientifically correct, so if you choose to evaluate that one post as an indicator of what I know, that is just great. There is nothing you have said that I did not know before, but thanks for the explanation anyway.

UlanBatori · Post by **UlanBatori** » 20 Feb 2016 22:23

The actual 'mean free path' for radiation is closer to 1 centimeter after electromagnetic effects are included. Light travels this distance in about 3 x 10^-11 seconds. Very approximately, this means that to travel the radius of the Sun, a photon will have to take (696,000 kilometers/1 centimeter)^2 = 5 x 10^21 steps. This will take, 5x10^21 x 3 x10^-11 = 1.5 x 10^11 seconds or since there are 3.1 x 10^7 seconds in a year, you get about 4,000 years.

This high-funda math completely went around my head like an infrared photon around a nanometer-sized particle. Exactly where is the delay in the photon's propagation in the above? ( No, I haven't done the math, the calculator is too far for me to reach from my chair..)

When I look at the line of ants going from the dead insect to the antihill, each ant interacts with the next one it meets for an instant, then moves on. But it still goes in an approx. straight line. So if its velocity is 3x10-3 meters per second, and it has to go 3 meters, it would take nominally take 1000 seconds. But due to the interactions, of which there may be 1000 if the ants are 6 mm apart, (phew! that took an hour to figure out! Mean Free Path is 3mm) then Mr. Ant encounters 1000 encounters. If each encounter took 0.5 seconds, Mr. Ant's journey takes 1000 + 0.5x1000 = 1500 seconds. Not a big deal.

So what is that calculation saying about the time for a photon/particle interaction? That it is >>>>>> vacuum transit time? Pls explain, that completely misses me.

Also, the interaction between a photon and a particle depends on the ratio of wavelength to particle size. When that is large, the photon/particle interaction is Rayleigh scattering - scatters a bit in all directions but essentially the photon goes on mostly unaffected. A visible light photon has a wavelength of ~ 0.5 micrometer, i.e., 500 nanometers. A proton is, what? << 1 nanometer? So the ratio in this case is around 500 - definitely Rayleigh scattering. I think a proton is <<1 nanometer, in fact.

So, what is the interaction time? Very interesting question indeed. I could not find it in the calculation above.

Also, if this 'interaction' is an absorption and then an emission, then is it the same photon traveling for 4000 years?
Reminds of of the story of George bin Washington's axe - the one he used to cut the cherry tree and got spanked. Remains intact today - OK, the blade has been changed 150 times, and the handle 340 times. 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?

member_29325 · Post by **member_29325** » 20 Feb 2016 22:57

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?

Don't think anyone can make a claim about a specific photon and prove it, but these are just estimates based on how close particles are packed inside a star. We can only measure aggregate effects, which are good enough for the most part. Talking of specific photons in a domain where statistical math and analysis is central to validating most theories does not make sense. IMO etc. with respect to the LIGO results, my current understanding is that the gravitational waves get a headstart over the gamma radiation emitted from the event (collpsing black holes) and the lag gives an idea of the density of the black holes, working backwards from the lag. All of this is legit, since we can only infer all of this based on proven existing theories. No one gets to travel or make measurements any other way.

Amber G. · Post by **Amber G.** » 20 Feb 2016 23:09

ranjan.rao wrote:Amber G, one question that I have is that are these waves also going to have impact on time part. So far I see only space part being talked about.

Very nice question, Let me take a stab, assuming I understand what you are asking. Please do reply if more clarity is needed, or if I am wrong or unclear. (Of course, good text books can be of help and you may already have your answer)

The "ripples" due to GW is not "ripples" in coordinate system so to speak (like longitude/latitude lines on a 2-D globe). Actually Einstein in 1916 paper was not very clear (in my opinion) and and so he was not sure that GW can be detected by LIGO type experiment.

It was, if I am not mistaken, around 1950's Feynman (and may be some others, I think) gave more clarity and if you see my previous post the GW will can be measured as forces like Tide will "bent" the masses a little. (This was actually the principle behind Weber bar type apparatus to measure GW -- which has been unsuccessful for last 50 years). There "arms" of LIGO are long (4Km) with masses (mirrors on the end), hence one was able to measure the change in distance.

This is not unlike EM waves which can cause electrons to oscillate in a dipole antena and one can receive radio signal.

The difference is that there are particles with + charge, neutral or even -ive charges, so the relative motion can be huge and easier to detect. This is how one can listen to radio much easier using EM waves.

Hope this helps.

member_29325 · Post by **member_29325** » 20 Feb 2016 23:15

UlanBatori · Post by **UlanBatori** » 20 Feb 2016 23:32

ThiruV wrote:
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?
Don't think anyone can make a claim about a specific photon and prove it, but these are just estimates

All understood, I know what "Mean Free Path" means - as in the ant example. But where is the delay induced by this interaction? It is like saying, Rajdhani express travels at 160kmph, but it stops at 100 stations for 1 minute each, so that's 100 minutes added. In the case of trains, add 2 mins delay for acceleration/deceleration which takes a long time, not so with light. So a) if AmberG is claiming that interaction time for photo/proton or photon/electron is long, then it cannot be the same photon traveling (relay race analogy).
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) 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...

member_29325 · Post by **member_29325** » 20 Feb 2016 23:49

TSJones · Post by **TSJones** » 20 Feb 2016 23:57

does not space time depend upon the conditions of the observer? just asking stupid question.......

member_29325 · Post by **member_29325** » 21 Feb 2016 00:06

member_22733 · Post by **member_22733** » 21 Feb 2016 00:16

Relativity of simultaneity is what you guys are talking about. Any two spatially separated events ocuring "simultaneously" in our (inertial) reference frame, will be non simultaneous in some other reference frame. So you can find an inertial reference frame for which any two spatially and temporally separated events in your reference frame appear to occur temporally at the same time in that reference frame.

Basically, velocity rotates the co-ordinate axis and there is one rotation where any two points appear perpendicular to the "t" axis.

member_29325 · Post by **member_29325** » 21 Feb 2016 00:26

UlanBatori · Post by **UlanBatori** » 21 Feb 2016 00:59

Hey, when the Sun comes up out of the ocean past the edge of the flat Earth tomorrow in its daily journey around the Earth, pls ask yourself: Is that photon that just reached your eyes time-dilated? Is there a 4000-year bureaucracy operating inside that red ball? Coordinate system is based on the straight line from your eye to the center of the Sun, OK, refracted by the atmosphere. I think that what looks like 4000 years to the photon inside the Sun (and can you blame it for wanting to get out, hain, there are Dumbbells doing a belly-dance there!**) is actually only 2.5 seconds to the observer outside. The time compression occurs when one accelerates AWAY from earth, not towards it, hain? And here there is no compression. Light starts travelling at local c, then becomes vacuum c.

** Explanation by Physicist based on Deep Mathematics. Not subject to question by mere mortals.

TSJones · Post by **TSJones** » 21 Feb 2016 02:29

UlanBatori wrote:Hey, when the Sun comes up out of the ocean past the edge of the flat Earth tomorrow in its daily journey around the Earth, pls ask yourself: Is that photon that just reached your eyes time-dilated? Is there a 4000-year bureaucracy operating inside that red ball? Coordinate system is based on the straight line from your eye to the center of the Sun, OK, refracted by the atmosphere. I think that what looks like 4000 years to the photon inside the Sun (and can you blame it for wanting to get out, hain, there are Dumbbells doing a belly-dance there!**) is actually only 2.5 seconds to the observer outside. The time compression occurs when one accelerates AWAY from earth, not towards it, hain? And here there is no compression. Light starts travelling at local c, then becomes vacuum c.

** Explanation by Physicist based on Deep Mathematics. Not subject to question by mere mortals.

uh, whatever you say, boss........head spinning....

member_22733 · Post by **member_22733** » 21 Feb 2016 02:51

"A Photon" does not take 4000 years to reach the sun's surface from its center. No time dilution filution here

.

A nuclear reaction usually involves energies in the gamma radiation range. That means ALL energy generated at the center of the sun is in gamma form initially. That then impacts the plasma surrounding the core, part of the energy is absorbed and transmited at a lower frequency. That then impacts some other part of the plasma, again part of it gets absorbed and then part gets transmitted, ad infinitum. At the surface of the sun it turns into a black body radiation type of thing (it thermalizes so to speak).

So to rephrase "a single photon" does not live long inside the sun, instead part of the "energy" produced at the nuclear core of the sun takes 4000 years to exit the surface "on an average" since there will be a tiny energy in the tail of the black-body spectrum which corresponds to gamma rays which may have found a hole in the plasma to exit directly outside.

If this process does not occur i.e. if sun's plasma layers do not interact with gamma rays, we would have been roasted out of existence long long time ago.

A_Gupta · Post by **A_Gupta** » 21 Feb 2016 02:55

UlanBatori wrote:
A_Gupta wrote:Nothing to do with mass distribution.
https://en.wikipedia.org/wiki/Tidal_locking
Ah! A classic case of dismissive non-pompously-arrogant Physics paper-parroting with technobabble in lieu of the sane, E-Z-2-samajh explanations that are a trademark of UBCN: If you read under your link, you might have found this:
Q and k_2 are generally very poorly known except for the Moon, which has k_2/Q=0.0011.

Yes, I read through. The paper from which that formula comes is here:
http://www.math.cornell.edu/~rand/randpdf/gladman.pdf

Reading on, we see that it is "tidal distortion", IOW, the tide pulls the surface of the Moon down towards it. Works for rubber balls, but the Moon is a bit rigid. Or something else that causes a slowdown in every rotation.

This is actually 19th century classical Newtonian physics. The gravitational stress is calculable to high accuracy, the strain and dissipation, however are strongly dependent on the material composition of the planet and satellite. Is the satellite rocky? does it have a fluid core? etc. etc. With the Earth-Moon system Q and k_2 are directly measurable. The tidal deformation is also measurable - the moon's surface deforms by as much as 10 centimeters, and the Earth's surface by as much as 50 centimeters. Since the Earth's diameter ~ 12,800 kilometers the strain is 0.5 meter/1.2 * 10^7 meter ~ 0.4 * 10^-7 which is a tiny strain; it is measurable because the earth is huge.

For other celestial systems, such measurements are not available.

What the Authority I mentioned, mentioned, was that they used all these sophisticated pissikobabble in lengthy Simulations lasting many years, and found that eventually it locked the Moon with the denser side (call it the Physicist Side because of the sheer Weightiness of it) facing the Earth. Have you found some evidence that it is the non-dense aka YakDung-head side that faces the Earth?

The asymmetry of the moon is a topic of ongoing research, e.g.,
http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2750.pdf

A_Gupta · Post by **A_Gupta** » 21 Feb 2016 03:01

About the time for photons to get from the Sun's interior to the surface, what LokeshC wrote.

member_29325 · Post by **member_29325** » 21 Feb 2016 03:05

Thanks, LokeshC, A_Gupta. And thanks to Amber G. for references and links.

OT: sucks that some of the PRL papers are priced 25$ per paper.

member_29325 · Post by **member_29325** » 21 Feb 2016 03:25

This one from 2008 explains what the LIGO detectors were designed to detect (different from other detectors that exist in Japan and EU). There are apparently 6 to 100 such events every year, though it is not necessary that the LIGO is sensitive enough to be able to detect all of them. Feels like I am back in +2 again.

http://arxiv.org/pdf/gr-qc/9501027v1.pdf

Vayutuvan · Post by **Vayutuvan** » 21 Feb 2016 06:13

AmberG ji: please answer my question - onlee.

UlanBatori · Post by **UlanBatori** » 21 Feb 2016 06:31

A_Gupta wrote:The asymmetry of the moon is a topic of ongoing research, e.g.,
http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2750.pdf

It may be a subject of research, but the point I made is very clear, from the same LPI paper:

Furthermore, this asymmetry is made more pronounced by the Moon’s center of mass (COM) being about 2 km closer to the Earth than its center of figure (COF) [1]

Q.E.D.
The asymmetry of the Moon is the cause of the troubles that ppl have, orbiting the Moon: there is huge g-jitter, much more than for Earth orbit.

johneeG · Post by **johneeG** » 21 Feb 2016 07:55

Amber G. wrote: Let me just add a trivia here. Which will send madarasa mathwala in a tizzy but ask any physics professor or do your own calculations . . 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.

Distance between Earth and Sun - 150 * 10^6 Km
Radius of Sun(distance between center of Sun and surface of sun) - 696,000 km

The time taken for light to travel from center of Sun to surface of sun - 4000 years = 4000 * 365 * 24 * 60 minutes = 2102400000 minutes.
The time taken for light to travel from surface of sun to Earth - 8 minutes 20 seconds.

The distance between earth and sun is more than the radius of Sun by - 215 times.

Time taken to travel lesser distance is 262800000 times more than the time taken to travel more distance.

Yea, apparantly, light takes more time to travel lesser distance. It seems that a photon takes 4000 years to travel the lesser distance and 8 minutes to travel 215 times more distance. Woah! If this is not nonsense, I don't know what is.

vishvak · Post by **vishvak** » 21 Feb 2016 08:04

Some details about photon diffusion time scale for the sun: link
Page 759, 760 - can be clicked on the left side. Per this, the diffusion time is about 17,000 years on average.

TSJones · Post by **TSJones** » 21 Feb 2016 08:08

johneeG wrote:
Amber G. wrote: Let me just add a trivia here. Which will send madarasa mathwala in a tizzy but ask any physics professor or do your own calculations . . 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.

Distance between Earth and Sun - 150 * 10^6 Km
Radius of Sun(distance between center of Sun and surface of sun) - 696,000 km

The time taken for light to travel from center of Sun to surface of sun - 4000 years = 4000 * 365 * 24 * 60 minutes = 2102400000 minutes.
The time taken for light to travel from surface of sun to Earth - 8 minutes 20 seconds.

The distance between earth and sun is more than the radius of Sun by - 215 times.

Time taken to travel lesser distance is 262800000 times more than the time taken to travel more distance.

Yea, apparantly, light takes more time to travel lesser distance. It seems that a photon takes 4000 years to travel the lesser distance and 8 minutes to travel 215 times more distance. Woah! If this is not nonsense, I don't know what is.

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:

Gamma rays are produced by nuclear fusion in stars including the Sun (such as the CNO cycle), but are absorbed or inelastically scattered by the stellar material before escaping and are not observable from Earth.

the surface of the sun is heated up and viola! there is light.

works for me for all i know. it's above my pay grade and not my MOS.....

this is the last message from me.......

johneeG · Post by **johneeG** » 21 Feb 2016 08:14

TSJones wrote:
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:

Gamma rays are produced by nuclear fusion in stars including the Sun (such as the CNO cycle), but are absorbed or inelastically scattered by the stellar material before escaping and are not observable from Earth.
the surface of the sun is heated up and viola! there is light.

works for me for all i know. it's above my pay grade.....

this is the last message from me.......

We are talking about the age of the photon which has travelled to earth from the center of the sun. So, this photon takes 4000 yrs to travel from the center to surface and then takes 8 minutes to travel from surface of the sun to the earth even though the radius of sun is 215 times shorter than the distance between sun and earth!!!

UlanBatori · Post by **UlanBatori** » 21 Feb 2016 08:22

Maybe it is Pathan, not Photan. Walks. 696000 km in 4000 years. Or, 174 km per year. One step in front of the other.

vishvak · Post by **vishvak** » 21 Feb 2016 08:23

Yes, johneeG sir, very well known phenomena called photon diffusion time scale. Some even claim that it takes millions of years for photons, formed at the center, to travel to the surface, by which time the gamma rays have lost a lot of energy and are not harmful anymore.

johneeG · Post by **johneeG** » 21 Feb 2016 08:41

The distance between the center of the sun and the surface of the sun - 696,000 Km - 696,000,000 m.
The time taken for the photon to travel from the center of the sun to the surface of the sun - 4000 yrs = 4000 * 365 * 24 * 60 * 60 seconds.

Then, the speed of photon(gamma ray or whatever) inside the sun is: 0.0055 m/s
Now, the constant speed of light(photon) outside the sun - 299,792,458 m / s

So, the speed of photon outside the sun is 299,792,458 m/s while the same photon traveled at the speed of 0.0055 m/s. So, suddenly, the photon increased its speed from 0.0055 to 299,792,458. That means the speed of photon increased 54 * 10^9 times suddenly as soon as it got out of the sun's surface. Oh, btw, no one has ever been inside the sun, so all these are speculations. Infact, 4000 years is just one of those speculations. There are other speculations which say that this photon actually could take 100 times longer(yep, 100 times longer than 4000 years) to travel from the center to the surface of the sun.

----
vishvak saar,
so they are basically saying that the photons are like drunkard as long as they are inside the sun. They are very slow and erratic. But, as soon as they outside the sun, they become very disciplined. They are not drunk anymore and their speed also increases by many times. It seems sun is like a bar for the photons where they get drunk and don't want to leave the place.

johneeG · Post by **johneeG** » 21 Feb 2016 08:49

UlanBatori wrote:Maybe it is Pathan, not Photan. Walks. 696000 km in 4000 years. Or, 174 km per year. One step in front of the other.

Then, once they leave the sun, photons become Usain Bolt. They cover a distance of 150 * 10^6 Km in just 8 minutes 20 seconds.

NRao · Post by **NRao** » 21 Feb 2016 08:50

Yea, apparantly, light takes more time to travel lesser distance. It seems that a photon takes 4000 years to travel the lesser distance and 8 minutes to travel 215 times more distance. Woah! If this is not nonsense, I don't know what is.

Is someone saying it takes that long to travel within the Sun? Is it due to the density or because the photons do/can not travel in a straight line?

Also, the 4000 years must be an average? So, a photon could zip in the fast lane and take a few years, while some could take eons. All ave 4000?

member_22733 · Post by **member_22733** » 21 Feb 2016 09:02

Photon has no age, since it travels at the speed limit, time and age are not meaningful properties of a photon. The only thing meaningful is the age and position of the event that caused the photon to come into existence, I.e. a point in spacetime of our reference frame.

When we detect a photon, we are detecting an event in spacetime of whose light cone we fall into. I.e photons are information carriers about changes in the universe. Ofcourse, by detecting that event we "destroy" the photon, I.e. the information is "scattered" away. Can also be viewed as the detector interacting with the event that created the photon.

The low probability of such interactions is what makes gravitational waves so important.

IMVVVHO.