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: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 29 Feb 2016 11:40

I put a nice (long) post but it went in a bit bucket...:( will post it later)

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 29 Feb 2016 12:04

I don't know if it is worthwhile to reconstruct my long(!) post but let me start by giving some background.. I will post about photon's path in next post but let me just post some thoughts..

Some random points -- needed for background..

- As I said a few posts ago, I will highly recommend Landau's "What is relativity". For those who do not know Lev Landau was one of the greatest mind in physics (many called him Soviet Union's Einstein). For those whose Russian is little rusty, the English translation, (I just checked) is available at Amazon dot com. Among other things, it will explain photons/light and why toll booth model may not be very useful.

***

The photons (light) propagation in air is similar in some ways to sound (and not cars or bullets)... the way they are similar: (Let us assume a fixed frequency for both sound and light)

-- The velocity does NOT depend on the source which generated it. (unlike bullet where the velocity coming out depends on the type of gun etc)

-- Like sound , after the photon (light) passes through a media, it's velocity changes, but when it comes out again in air the velocity resumes to original velocity. (unlike bullet - if a bullet passes through a sand bag it will slow down when it comes out and will remain slow for the rest of the path)

-- The velocity does not depend on the speed of the source.

-- The velocity is same in all directions if the you are at "rest" (Now for sound one can have "rest" defined as "rest with respect to surrounding air",, but for light it presents problem as light can go through vacuum)
(To understand and resolve the difficulty presented by this "rest", one has to understand theory of relativity)

But there are some other ways where photon does not behave like a wave... and more like a bullet.
But you really have to understand before you blindly start applying "toll booth scattering theory" for photons.

***

When one sends a text message (or email), one can do a "tracert" type command to see how the message got from point A to point B. There may not be any SINGLE "electron" or physical particle moved (and got stored and forwarded between intermediate servers) along.. but it still make sense to trace the "message route" and time delay. Same thing for photon ... or energy generated from the core of the sun to coming to a solar panel on earth..

More of this in the next post.

But hope this helps.

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 29 Feb 2016 12:33

For that photon journey...

Let us consider a solar panel on earth.. where does the energy come from. From Sun. More accurately fusion reaction (read all about it in nuke dhaga on how to make fusion bombs :)) where hydrogen fuses into helium. In the process every second about 4 million tons of mass gets converted into energy in the form of photons (gamma rays)..

But let us put a "tracert " on this.. how that energy reaches our solar panel.

But first look at a structure/layer of sun.. for example here:
http://www.nasa.gov/mission_pages/iris/multimedia/layerzoo.html

The Core
All of the energy the Sun eventually radiates is created in the core. The temperature is about 14,000,000° C high enough to fuse hydrogen. Every second the energy produced is about 4000000 tons of matter -- mainly in terms of photons (gamma rays) . Neutrinos are also produced. These do not react with matter and zoom out of the Sun in about a few seconds. The main energy is in terms of photons (gamma rays). Because the Sun's core is very dense (10x lead) and because of the state of the atoms in the core, the photons are not reabsorbed into the core. Instead, they bounce around for a very long time. (This is where 4000+ years etc make perfect sense). Some photons ,after doing enough bouncing go to:

The Radiative Zone
The radiative zone is a layer of highly ionized gas. Because most of the atoms here lack electrons, they can't absorb photons for convection to the surface. Most photons just bounce around. Every once in a while a photon will be absorbed. It will later be re-emitted as a photon with less energy (X-ray or UV ray) Eventually, photons along the entire magnetic spectrum exist in the radiative zone... and we go to:

The Convective Zone
This is like a hot tandoor. In this zone, gases are cool enough and enough of a temperature gradient exists that convection can happen. Also the atoms of this zone can absorb the photons because they are less ionized. So it absorbs energy from the radiative zone. This energy heats it, and it rises to the next layer:

The Photosphere
The photosphere (only about 100 miles deep). Same elements as the radiative zone but temperature =6,000° C.. Black body radiation gives off photons consistent with theory...

These photons (or EM waves if you prefer) travels to the solar panel on earth..

Hope this is useful. Hope it encourages one to read more about it.

UlanBatori
BRF Oldie
Posts: 9077
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby UlanBatori » 29 Feb 2016 16:42

photons are little different than cars and so one has to be little careful applying models which may seem good but do not agree with experimental results. The critical difference is - if a photon(= light) passes through a medium, it slows down, but as soon as it out, it resumes its speed of c.


Another example of thinking-challenge. Dismissing thoughtful argument based on dogma.

A car coming out of a toll booth also accelerates to the speed it had b4 entering the tollbooth. Surely that wasn't so hard to figure out? IOW, the car adjusts to the speed appropriate for the medium where it is propagating. Just like the photon. This is the analogy and it is accurate, I know enough kindergarten physics to have figured that out for myself, no need to sit where generations of physicists sat, etc.

No one is talking of bullets here. HOW does the photon accelerate is a question for which I have no answer. This magic of "Now It Is a Wave, Now It is a Particle", is beyond my poor brain. I honestly do not understand how an e-mag wave exists in a vacuum, unless the wave has some mass associated with it. In which case it must take finite time to accelerate. If someone can explain that without just posting a link to more "4000/71000 years" type garbage I would appreciate it.

The entry point that I used to break into the Fortresses Of Dogma is Post #53 of the link that A_Gupta posted. I don't know all the basis of the points made there, but the points made sense:
a) Simple conservation of momentum holds for a photon/particle interaction: it is **NOT** a case of energy transfer into a specific energy mode. (why, I don't know). But if this is the case, the electron's kinetic energy surely increased, so did its momentum, like a toll booth pushed down the highway by the SUV that collided head-on.
b) After ~10^-15 seconds a new photon is emitted. (I had thought it was 10^-12 based on some prior Wikipedia entry, but what's a factor of a 1000 in this business?
c) The emitted photon has the SAME MOMENTUM as the incident one (magnitude and direction). Presumably the reaction slammed the electron back to its original momentum.

True to form, the experts here have absolutely not gone and contradicted a (presumed) fellow Physicist (postor of Post 53) but just continued to sneer at me, just parroting stuff from outdated textbooks written by (who else) fellow physicists.

So please tell me that items (a) through (c) are wrong (not just secondary or tertiary effects such as positrons and anti-electrons of which I know nothing) and why, using clear logic, AFTER reading and quoting that Post 53, and I may begin to regain some respect for said physicists. If positrons shoot off during the interaction, then the mass of the whole system (electron+ photon) has reduced, so when the photon is emitted it cannot have the same momentum as the incident photon. Post 53 says this is absolutely not the case.

Please stop the personal attacks, I've been way too patient, does not imply any unilateral disarmament. I too can start grading the professional competence of other postors in public, naming names. No need to bring in Alma Maters (very personal insult to us Mongolians). No need to bring in presumed personal info of postors. These are all losers' strategies employed when logic is seen to be unsustainable. If I want to post deep research findings, I do that in the All-Mongolian Beer-Reviewed Journal of Deep Research, not on Internet fora (that's plural of 'forum' in pucca Latin). :mrgreen:

As for "Measurements always trump dogma", may I point out with all due respect that per Heisenberg's Uncertainty Unprinciple, you cannot measure the position and energy of the tollbooth accurately at the same time? If that's not dogma I don't know what is. Bose-Einstein condensates have stopped whole atoms cold, no pun intended. Position and energy both known, its in that bottle and its stopped. Zero momentum. My Nobel Laureate said so, and he trumps anyone whose texts you have read etc. Live. OK, maybe slightly inebriated, but live. :rotfl:
Last edited by UlanBatori on 29 Feb 2016 17:07, edited 2 times in total.

UlanBatori
BRF Oldie
Posts: 9077
Joined: 11 Aug 2016 06:14

Re: Physics Thread.

Postby UlanBatori » 29 Feb 2016 16:52

The Photosphere
The photosphere (only about 100 miles deep). Same elements as the radiative zone but temperature =6,000° C.. Black body radiation gives off photons consistent with theory...


Solar flaresare tens/hundreds of thousands of miles in extent. 100 miles is rather small to be counted as a region at all, in this context: a body of 696,000 km radius (why not 700,000? It's all gas!) So this model of the Sun as a nice stable sphere is all wrong. It's like dividing the Earth's atmosphere into nice hard layers. 10cm thick.
If one reads a little beyond the parroted headline, motivated by a slight scientific/engineering sense and curiosity, one finds:
The point where it appears to become completely opaque is called the photosphere. Thus, the photosphere may be thought of as the imaginary surface from which the solar light that we see appears to be emitted.


In other words, the claimed thickness of the layer is the depth to which present instruments can see. They could have said more honestly:

V ain't got no clue hwhat's below about 100 km into da Sun 'coz v cyaint see

Bade
BRF Oldie
Posts: 7212
Joined: 23 May 2002 11:31
Location: badenberg in US administered part of America

Re: Physics Thread.

Postby Bade » 29 Feb 2016 17:12

I am sorry but UB you do not want to learn but just argue (as another physicist said for the wrong reasons and end with the wrong conclusions with no supporting data), I am now free to invoke my rights and report you as just a simple troll. Adios !

What a waste of yesterdin it was. :(( :(( like all other threads these days this one too. So I need to find useful things to do than argue with a wall. :rotfl:

A_Gupta
BRF Oldie
Posts: 10297
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 29 Feb 2016 18:35

This magic of "Now It Is a Wave, Now It is a Particle", is beyond my poor brain.


UBji, ultimately, the mathematics is precise and only the mathematics is precise. Human natural language can only be a metaphor for how the photon behaves. A useful shorthand way to think about the photon is that the photon propagates as a wave, but is measured as a particle.

I honestly do not understand how an e-mag wave exists in a vacuum, unless the wave has some mass associated with it.


Can an electric field exist in a vacuum? Can a magnetic field exist in a vacuum? Once we've answered that, the electromagnetic wave becomes trivial.

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 29 Feb 2016 21:34

Few comments: I hoped that my post will encourage people to read up some more and learn..but was not surprised so see UB's post(s) in response ..I too have no particular desire to debate with a wall but these points may be helpful to others..
A car coming out of a toll booth also accelerates to the speed it had b4 entering the tollbooth

Not really. NOT exactly the same speed! That is the point. Unlike cars, photons do not have "traffic jams". A very bright light (lots of photons) is not slower..and unlike a car, the velocity remains constant (VERY CONSTANT) as long as it is passing through vacuum (or same media). BIG difference.

-- I did not name all the layers of Sun. If one is really interested, any good source will tell that:

Photosphere is indeed about 100 miles deep but there are other layers, above photosphere like Chromosphere Transition Region and Corona where flares and other cool (:)) things take place.
Again my point was just to point in the direction where one can read more, explain things to those who are interested in learning things.

PS - UBji, I too have reported a few of your posts as I think enough is enough, may be this trolling is not as cool as you think.

sudarshan
BRFite
Posts: 1660
Joined: 09 Aug 2008 08:56

Re: Physics Thread.

Postby sudarshan » 29 Feb 2016 22:00

Ultimately, what happened with the random walk? Is it a valid model for photon transport in the solar interior, or is it not? :-? Can somebody give me a succinct explanation for either case without dripping sarcasm and a whole lot of obscure witticisms?

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 29 Feb 2016 22:10

UlanBatori wrote:
The Photosphere
The photosphere (only about 100 miles deep). Same elements as the radiative zone but temperature =6,000° C.. Black body radiation gives off photons consistent with theory...


Solar flaresare tens/hundreds of thousands of miles in extent. 100 miles is rather small to be counted as a region at all, in this context: a body of 696,000 km radius (why not 700,000? It's all gas!) So this model of the Sun as a nice stable sphere is all wrong. It's like dividing the Earth's atmosphere into nice hard layers. 10cm thick.


NOT really. Sun has been studied for years, any good text book can explain it further but the layers are fairly accurately described. Including what they are made out of. This is NOT just theory but experimental observation gathered by many different methods. And as my post said flares are not really a part of photosphere but rather considered part of other outer layers. But then, if you were really interested in learning, you could have found this out by reading any good source.

If one reads a little beyond the parroted headline, motivated by a slight scientific/engineering sense and curiosity, one finds:
The point where it appears to become completely opaque is called the photosphere. Thus, the photosphere may be thought of as the imaginary surface from which the solar light that we see appears to be emitted.


Nothing "imaginary" about it in the way you think. "opaque" may be in the sense that you can not "see" in visible wave lengths below this, but we observe cosmic rays, neutrinos etc.. have pretty good idea of what's inside.

In other words, the claimed thickness of the layer is the depth to which present instruments can see. They could have said more honestly:

V ain't got no clue hwhat's below about 100 km into da Sun 'coz v cyaint see


More apt will be for you to say that you have no clue as to how scientific method works. One does not have to go to the Sun, or even "see" in visible light to learn about layers.

For example, read up, how Helium was discovered. It was discovered on Sun (by looking at spectra) before one found it on earth.

Physics is not endless story telling about green goo and mocking scientists that "they don't have a clue".. it is not even looking up wiki to score a debating point...
As I said
Learning Physics Is Tough. Get Used to It

I hope you have some respect left for other forum members to thank me for all the time I have taken.

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 29 Feb 2016 22:22

sudarshan wrote:Ultimately, what happened with the random walk? Is it a valid model for photon transport in the solar interior, or is it not? :-? Can somebody give me a succinct explanation for either case without dripping sarcasm and a whole lot of obscure witticisms?


I don't know exactly which model you are talking about. if you are referring to TSJ's original post, I think it is a fairly good and valid model. Remember, it is just a model, and as long as the result is within the range the model claims it ought to be, it is good. In my humble opinion, and given that I have just glanced at it, it's quite valid and giving results consistent with observational data.

(What makes the model valid that in the core (see my previous message) the state of the matter is such that photons are not absorbed and thus the random walk type model has validity. In outer layers of the sun, it won't be as valid, and convection type heating model may be more valid in Convective Zone where photons are easily absorbed)

But critical part here is NOT to take my (or anyone else's) word alone for this, just check out the mathematical consistency etc.

UB's interpretation, and toll booth model do not make any sense. It is not mathematically consistent within even the same post... he does not even mention or give precise value of the energy of gamma rays at any particular stage or check if the math is even valid...

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

Re: Physics Thread.

Postby member_22733 » 29 Feb 2016 22:49

UlanBatori wrote:
No one is talking of bullets here. HOW does the photon accelerate is a question for which I have no answer. This magic of "Now It Is a Wave, Now It is a Particle", is beyond my poor brain. I honestly do not understand how an e-mag wave exists in a vacuum, unless the wave has some mass associated with it. In which case it must take finite time to accelerate. If someone can explain that without just posting a link to more "4000/71000 years" type garbage I would appreciate it.

The entry point that I used to break into the Fortresses Of Dogma is Post #53 of the link that A_Gupta posted. I don't know all the basis of the points made there, but the points made sense:


A_Guptaji has given a good analogy above on the wave/particle stuff.

QM is wierd, i.e. the wave function is a wave that propagates in a completely deterministic fashion, you can predict the time evolution of the wave function very exactly.

But the wave function is an abstract concept (IMVVVHO, although some people are calling it real), and it is also not directly observable. The only thing you can do with it is to perform measurements on it, and you do that by running operators.

Position is one operator, momentum is another. Now these operators have a special property, they are continous functions and are fourier transforms of each other. That creates a familiar problem (to atleast us Electrical engineers), you have a sharp window of measurement for position, your momentum measurement goes out of whack (fourier transform of an impulse == sinusoid over the entire range). Vice versa.

What you intend to measure is important in QM. If you intend to measure momentum accurately, you sharpen you momentum measurement window and your position operator cannot function.

Moreover, once you measure it, the wavefunction is detroyed and a new one takes its place. In all this none of the symetry laws are broken. (atleast I remember that from my QM courses eons ago).

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 29 Feb 2016 23:32

A_Gupta wrote:
I just learned this: the Kelvin-Helmholtz timescale is the time for the sun to radiate away all its energy if we can imagine its fusion reaction shuts down. This is of the order of 10^7 years, precisely because of radiative diffusion. Some good slides are here:
http://www.astro.caltech.edu/~george/ay ... -Lec7x.pdf


Thanks, indeed some good material.

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

Re: Physics Thread.

Postby member_22733 » 29 Feb 2016 23:43

^^^ It explains stuff so lucidly :). I have not struggled with one equation in that stuff so far. Very good indeed (especially for a layman nobody like me).

sudarshan
BRFite
Posts: 1660
Joined: 09 Aug 2008 08:56

Re: Physics Thread.

Postby sudarshan » 29 Feb 2016 23:48

AmberG, thanks ma'am. The random walk had to do with modeling photon travel with multiple collisions in the path. Like a drunkard goes one step forward, one to the right, then forward, left, backwards.... I'm sure you know that distance from the initial point will increase (statistically) as square root of time in this case.

So when people model this and say "photons take on average 4000 years to reach the surface of the sun from the center," that is a very crude estimate, and of course we have only models to predict what happens in the sun (with some observations). 4000 years is just the prediction from one pretty simplistic model, and it's to be taken with a dose of salt. Don't know why that had UB saab flying off the handle.

Bade
BRF Oldie
Posts: 7212
Joined: 23 May 2002 11:31
Location: badenberg in US administered part of America

Re: Physics Thread.

Postby Bade » 01 Mar 2016 00:09

If I may, the only crude part of the estimate is perhaps the width of each layers of the sun to be used...but otherwise it is a standard approach to calculate a random phenomena (assuming a gaussian distribution). We do not know exactly what each photon is doing, but statistically one can estimate and cross check with other data how long it takes.

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 01 Mar 2016 00:38

sudarshan wrote:AmberG, thanks ma'am. The random walk had to do with modeling photon travel with multiple collisions in the path. Like a drunkard goes one step forward, one to the right, then forward, left, backwards.... I'm sure you know that distance from the initial point will increase (statistically) as square root of time in this case.

So when people model this and say "photons take on average 4000 years to reach the surface of the sun from the center," that is a very crude estimate, and of course we have only models to predict what happens in the sun (with some observations). 4000 years is just the prediction from one pretty simplistic model, and it's to be taken with a dose of salt. Don't know why that had UB saab flying off the handle.

Essentially correct, it is a very crude estimate, and if I understood A_Gupta's post, it was given as a home work problem. Of course there are much more detailed models and may require more complicated math but 'random walk' type approach is quite powerful. (And yes, as you said, the distance goes as square root of the number of steps*average steps).

Since there is so much confusion created, and in spite of Bade and others attempts to point out that photon's in the core (gamma rays) and environment in the core make those electron photon scattering type explanations of TUT no sense.

Without going in too much math - (Again this can be confirmed by any good source) this is what happens inside the core -- put in simple terms but still useful in understanding fundamentals :

(I am putting some quantitative numbers for perspective, they may not be exact but are close to actual values for Sun. One can easily read up good source for more clarity)

At the core there is nuclear fusion. Every second about 600 million tons of hydrogen fuses into helium loosing about 4 million tons in the process and thus creating some 400 billion billion megawatts of power. Let us explore this -- again I will keep it simple..

This is proton-proton reaction (involves H+ ions). Two protons collide. It takes about 7 BILLION years on average for a proton to find another proton but there are many protons inside the core. When they collide they are moving with high velocity (remember both protons are +ively charged so they must be really fast to overcome the electric force and collide head on). Only a few protons collide (if there are too many collisions sun will explode) but they fuse.

The two-proton nucleus is very unstable, so one of the protons immediately decays into a neutron, neutrino and a positron. The positron eventually collides with an electron and they both turn into gamma rays (photons). The neutrino leaves the Sun at nearly light-speed, taking only a few seconds.

The new proton-neutron nucleus, (a deuterium) is very reactive, and it takes only a few seconds for it to collide with a proton. This collision releases another gamma ray. The new nucleus has two protons and one neutron.
This nucleus takes - on average - 400,000 years to find another nucleus just like it. These two collide, forming a nucleus with four protons and two neutrons. But two protons get knocked off by the force of the collision, leaving a stable helium nucleus with two protons and two neutrons.

The helium nucleus weighs only 99.3 percent as much as the four protons that went into the reaction to create it. The missing .7 percent gets converted into energy (E=mc^2)..

And the model of random walk still produces excellent results without taking into account all that..:)

(Hope this helps, if nothing else it may encourage some to read up on it.. there are many good books)

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 01 Mar 2016 02:39

Meanwhile in the news:

India to have lab for studying gravitational waves: PM Modi in 'Mann Ki Baat'
8) 8)

New Delhi: India has decided to establish a Laser Interferometer Gravitational-Wave Observatory (LIGO) where gravitational waves can be studied, Prime Minister Narendra Modi announced on Sunday.

In his monthly radio programme Mann ki Baat, Modi said Indian scientists were also in the research team that studied gravitational waves.

The laboratory will be third of its kind in the world after Hanford in Washington and Livingston in Louisiana, both in the US.

"Recently the Gravitational Waves have been discovered by the scientific community of the world, which is indeed a major achievement. We should be proud of the fact that Indian scientists were also part of it. Keeping this in mind, we have taken a decision to open a LIGO (Laser Interferometer Gravitational-Wave Observatory) in India," said Modi.

LIGO is a national facility for gravitational-wave research, providing opportunities for the broader scientific community to participate in detector development, observation, and data analysis.

The prime minister announced that within its limited resources India will also participate and contribute in the research through the LIGO.

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 01 Mar 2016 03:34

https://soundcloud.com/narendramodi/pm-modis-mann-ki-baat-february-2016
Extremely impressed with NaMo's Mann ki baat, the above link is original but I am sure the translation in your own language is available.

He talks about National Science Day, ( Feb 28, Anniversary of the discovery of Raman Effect), scientific methods, how curiosity makes a scientist etc.. and it looks like he was very well briefed when he talked about Discovery of Gravitational Waves and LIGO.

Worth Listening or looking up the text. (The total length is about 30 minutes, last 5 minutes is about science).

Raja Bose
BRF Oldie
Posts: 19481
Joined: 18 Oct 2005 01:38

Re: Physics Thread.

Postby Raja Bose » 01 Mar 2016 04:06

UB, Amber G, Bade JohneeG - agree to disagree and call it quits please. You guys can fill another 100 pages and still not agree on anything so let's just put an end to this and just agree that mongolians and physicists do not see eye to eye without poking out each other's eyes. Very unlike the good ol' days when SN Bose wrote in chaste Bengali to my grandpa (a non-physicist) to inquire about his chai biskoot with Einstein while vising IAS and didn't forget to ask how he was managing the toilet paper situation. (found that airmail letter last week).

TLDR; ADMIN NOTE: Further arguments will invite bans coz the time for warnings is long past after people did not listen to ramana's polite request.

Neshant
BRF Oldie
Posts: 4220
Joined: 01 Jan 1970 05:30

Re: Physics Thread.

Postby Neshant » 01 Mar 2016 05:09

UlanBatori wrote:A car coming out of a toll booth also accelerates to the speed it had b4 entering the tollbooth. Surely that wasn't so hard to figure out? IOW, the car adjusts to the speed appropriate for the medium where it is propagating. Just like the photon. This is the analogy and it is accurate, I know enough kindergarten physics to have figured that out for myself, no need to sit where generations of physicists sat, etc.



Not that I know a thing about physics... but I don't think this is an accurate analogy.

Light does not accelerate or decelerate. Its speed is a constant. So unlike a car that accelerates upto a certain speed, light is always c.

I think what happens when light goes through a medium is that it is absorbed and retransmitted many many times. That's what slows it down - not the time it takes to accelerate upto c (its always c!). Between the re-transmission and re-absorption within the material, its speed is c (for a very very short distance).

That's the only way I can think of how the speed of light through a medium can be slower than in a vacuum... and yet not violate the principle that the speed of light is a constant. Can there be any other way? I doubt.

Anyway can we leave this matter aside and move onto more important matters - like the Bob Lazar interview I posted 8)

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

Re: Physics Thread.

Postby TSJones » 01 Mar 2016 06:44

Sri Neshant,

the speed of light slows down to about 200,000 km/sec going through glass.

if photons are absorbed how do they transmit the view from the other side of the glass?

serious question, Neshantji.

thanks in advance......

Amber G.
BRF Oldie
Posts: 5978
Joined: 17 Dec 2002 12:31
Location: Ohio, USA

Re: Physics Thread.

Postby Amber G. » 01 Mar 2016 07:21

This is most likely my last message in this thread. I have put many posts in this thread for years and I am glad that many found my posts useful and thanked me over the time. But now I see there is no point to continue, specially when I see:

Raja Bose wrote:UB, Amber G, Bade - agree to disagree and call it quits please. You guys can fill another 100 pages and still not agree on anything so let's just put an end to this and just agree that mongolians and physicists do not see eye to eye without poking out each other's eyes. Very unlike the good ol' days when SN Bose wrote in chaste Bengali to my grandpa (a non-physicist) to inquire about his chai biskoot with Einstein while vising IAS and didn't forget to ask how he was managing the toilet paper situation. (found that airmail letter last week).

TLDR; ADMIN NOTE: Further arguments will invite bans coz the time for warnings is long past after people did not listen to ramana's polite request.


Speaking for my self, I have no intention of poking anyone's eye and frankly have not seen any one else here even remotely poking at each others eyes. As to Ramana's polite request, the above post, more than any other, is the one which is off-topic.. while the following uses funny language in addition of being off-topic:
Raja Bose wrote:Ah the hand waving (did I say wave? :eek: ) is in phultu flow....narayan narayan.....


I am reporting the above messages as I think those are off topic, if not trolling and rude. It does not contribute anything positive to the thread.

Folks - Even for the recent topic -- I put the news item for GW wave, copied PRL paper, gave mine and other scientists perspective, as an expert answered people's questions, put news item about LIGO in India. I used my considerable time, putting some excellent posts -- especially after the request of Ramana I gave some more useful info in layman's language. I appreciate the thanks I received.

Similarly Bade have put some excellent resources, explained some excellent points in clear terms. He deserves our thanks and not a brf admin's rebuke.

Brf should be grateful to contributors like me, Badeji, and and others and there is no need to be rude.

It will be helpful if this brf admin actually points out (with pm or here - either is fine) which posts are problems for him. No one is trying to convince anyone of any particular thing. My posts had VERY GOOD technical information, were educational and most were put in the hope that people will be encouraged to learn more. I have nothing to sell. We certainly do not deserve RB's rude remarks.

As a brf oldie I would find it unfortunate if brf does not remain a forum where one can discuss technical topics.

So I will wait at least till brf admin brings some clarity. Wish you all well.

Bade
BRF Oldie
Posts: 7212
Joined: 23 May 2002 11:31
Location: badenberg in US administered part of America

Re: Physics Thread.

Postby Bade » 01 Mar 2016 07:49

Amber_G, as a significant contributor here in this thread, I would say soldier on. The barbs need to be warded off for the good of society. Cannot lose this fight to be free to reason logically to the dark forces. Too many threads have fallen prey to this of late.

Many have mistaken the exchanges in this thread as debating points. Far from it. As for me, it never was to win a debating point, but to learn and share what I know. False ideas need to be called out as they sow even more confusion in gullible minds.

Neshant
BRF Oldie
Posts: 4220
Joined: 01 Jan 1970 05:30

Re: Physics Thread.

Postby Neshant » 01 Mar 2016 09:33

TSJones wrote:Sri Neshant,

the speed of light slows down to about 200,000 km/sec going through glass.

if photons are absorbed how do they transmit the view from the other side of the glass?

serious question, Neshantji.

thanks in advance......


There is no way light "slows down". From what I understand, its speed is always a constant.

What takes time for light to propagate through a medium like glass is the absorption and retransmission of a photon as it goes from one atom to another. Kind of like a relay race where each atom is passing the baton (photon) to the next atom. Except the baton (or photon in this case) that entered the glass is not the same one that leaves the glass.

Essentially the energy level of the atom is raised when the photon is absorbed. Since that configuration is unstable the energy level falls back to its normal state and the photon is re-transmitted.

That's my lay man's understanding of what's going on.

To say that light "slows down" is a violation of Einstein's claim that light is the only thing of constant speed in the universe. Constant meaning constant everywhere and always with no exceptions.

Vayutuvan
BRF Oldie
Posts: 9849
Joined: 20 Jun 2011 04:36

Re: Physics Thread.

Postby Vayutuvan » 01 Mar 2016 09:36

Two things electron positron pairs immediately annihilate and release energy (in the form of gamma rays? What frequency?). Secondly my money is on NIF. That's what Modi ji need to fund. Definitely more fusion bang for the buck instead of waiting for a century or more for the returns if any. LIGO shouldn't have been funded, IM very HO.

Outta here for the moment.

Suraj
Forum Moderator
Posts: 11427
Joined: 20 Jan 2002 12:31

Re: Physics Thread.

Postby Suraj » 01 Mar 2016 13:08

Admin Note

This thread is being locked for the time being, until it's decided what to do about it.

Raja Bose
BRF Oldie
Posts: 19481
Joined: 18 Oct 2005 01:38

Re: Physics Thread.

Postby Raja Bose » 02 Mar 2016 04:02

Admin Note

@Bade I meant to informally warn JohneeG rather than you in my previous post. My apologies.

---

@Amber G.

You are skating on very very thin ice here and have been warned. You are a regular member of BRF just like the rest of us here however much you crave some exalted status where others will genuflect and bow to your knowledge and credentials. This is the 2nd time I have seen you troll admins in recent memory and after discussing with others, apparently its an old habit with you. If I see you pull one more stunt like this and observe you indulge in this pompous self-appointed admin act of yours on BRF in the future, I will ban you. 3 strikes out - no questions asked. How is that for clarity?

This thread will stay locked for a few days while folks cool down and are able to resume discussion in a civilized manner again.

Neshant
BRF Oldie
Posts: 4220
Joined: 01 Jan 1970 05:30

Re: Physics Thread.

Postby Neshant » 15 Mar 2016 06:43

Interesting documentary from the 80s on an inventor trying to develop an "anti-gravity" machine.

It looks to be some kind of gyroscopic mechanism where the net force of two spinning gyros are channeled forward - for forward (or upward) momentum. This is as opposed to combustion propellant process which powers all gasoline/rocket engines where something has to come flying out the back to propel the object forward. In this case, nothing comes out the back.

The machine (which sounds rather simple) is described. What do you physics pros think of it?

India needs such "mad scientist" types which the west has in great abundance - at least until recent times when banking crooks started up with their scams of indenturing/impoverishing productive people into perpetual debt slavery schemes.

Anti-Gravity Machine (part one)


Anti-Gravity Machine (part two)

Mort Walker
BRF Oldie
Posts: 6766
Joined: 31 May 2004 11:31
Location: The rings around Uranus.

Re: Physics Thread.

Postby Mort Walker » 15 Mar 2016 08:53

^^^This sort of stuff has been around for several decades. Remember energy is conserved and the 2nd law of thermodynamics is always valid.

In India, we've had charlatans like this too. Remember the herbal petrol fellow in Tamil Nadu about 16 years back?

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

Re: Physics Thread.

Postby member_22733 » 15 Mar 2016 09:00

OMG. This thread again.... :mrgreen:

There was a Russian Ceramics guy who took a superconducting ceramic disk and rotated it at like 6000rpm and "discovered" that things weigh a little lighter above such things.

http://www.wired.com/1998/03/antigravity/

However, its likely that no one ever managed to reproduce it (and is likely a crackpot idea). NASA had a "secret team" working on this project (if they did see any progress they probably have kept it secret :) )

Yayavar
BRF Oldie
Posts: 4761
Joined: 06 Jun 2008 10:55

Re: Physics Thread.

Postby Yayavar » 15 Mar 2016 09:06

^^in fluid or vaccuum ?? :D

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

Re: Physics Thread.

Postby member_22733 » 15 Mar 2016 09:18

:lol: in vacuum.

Actually, this paper shows a way on how such anti-gravity claims can be verified, including a theoretically valid way to create an artificial perturbation of gravity (section V)

http://arxiv.org/pdf/1504.00333v3.pdf

Basically have a modified interferometer (with millions of passes over the supposed altered gravity field).

Neshant
BRF Oldie
Posts: 4220
Joined: 01 Jan 1970 05:30

Re: Physics Thread.

Postby Neshant » 16 Mar 2016 00:59

What I found interesting is his claim that a space craft could be moved and accelerated without stuff shooting out the back.

If an on-board nuclear reactor was spinning those gyros in the way he described, could it actually generate forward momentum. Does it not need something to react against.

I can't think of any other way a craft could be moved forward in space without something shooting out the back unless its large sails catching the solar winds or some laser from earth pushing it forward (i.e. something external). Yea you can sling shot the craft around a planet but that won't get as much speed as gradual and constant acceleration.

That being said, no "conventional" apparatus has ever broken the laws of Thermodynamics.

Also please don't bring up other stuff like "herbal petrol". Everything deserves to be analysed and debunked on its own merit. Straw man arguments citing something else to debunk or justify doesn't lend validity to the argument.

One great thing about the west is these "mad scientists" are always trying something new. Chances of any great breakthrough no doubt approaches zero - especially if its some simple mechanical device claiming to do the extra-ordinary. But the mere process of experimenting & tinkering around is what innovation & creativity is all about. It sure beats banking & bullshitting which is a 100% useless activity.

Prem
BRF Oldie
Posts: 20734
Joined: 01 Jul 1999 11:31
Location: Weighing and Waiting 8T Yconomy

Re: Physics Thread.

Postby Prem » 17 Mar 2016 04:14

http://www.mirror.co.uk/news/technology ... -dazzling-
Black hole spotted emitting dazzling red flashes with the power of 1,000 suns
In June 2015, a black hole called V404 Cygni underwent dramatic brightening for about two weeks, as it devoured material that it had stripped off an orbiting companion star.V404 Cygni, which is about 7,800 light years from Earth, was the first definitive black hole to be identified in our galaxy and can appear extremely bright when it is actively devouring material.In a new study, published in the journal Monthly Notices of the Royal Astronomical Society, an international team of astronomers, led by the University of Southampton, report that the black hole emitted dazzling red flashes lasting just fractions of a second, as it blasted out material that it could not swallow.The astronomers associated the red colour with fast-moving jets of matter which were ejected from close to the black hole.These observations provide new insights into the formation of such jets and extreme black hole phenomena.Dr Poshak Gandhi, associate professor at the University of Southampton, said: "The very high speed tells us that the region where this red light is being emitted must be very compact."Piecing together clues about the colour, speed, and the power of these flashes, we conclude that this light is being emitted from the base of the black hole jet. The origin of these jets is still unknown, although strong magnetic fields are suspected to play a role."Furthermore, these red flashes were found to be strongest at the peak of the black hole's feeding frenzy. We speculate that when the black hole was being rapidly force-fed by its companion orbiting star, it reacted violently by spewing out some of the material as a fast-moving jet.

Mort Walker
BRF Oldie
Posts: 6766
Joined: 31 May 2004 11:31
Location: The rings around Uranus.

Re: Physics Thread.

Postby Mort Walker » 18 Mar 2016 04:41

Neshant wrote:What I found interesting is his claim that a space craft could be moved and accelerated without stuff shooting out the back.

If an on-board nuclear reactor was spinning those gyros in the way he described, could it actually generate forward momentum. Does it not need something to react against.

I can't think of any other way a craft could be moved forward in space without something shooting out the back unless its large sails catching the solar winds or some laser from earth pushing it forward (i.e. something external). Yea you can sling shot the craft around a planet but that won't get as much speed as gradual and constant acceleration.

That being said, no "conventional" apparatus has ever broken the laws of Thermodynamics.

Also please don't bring up other stuff like "herbal petrol". Everything deserves to be analysed and debunked on its own merit. Straw man arguments citing something else to debunk or justify doesn't lend validity to the argument.

One great thing about the west is these "mad scientists" are always trying something new. Chances of any great breakthrough no doubt approaches zero - especially if its some simple mechanical device claiming to do the extra-ordinary. But the mere process of experimenting & tinkering around is what innovation & creativity is all about. It sure beats banking & bullshitting which is a 100% useless activity.


A nuclear reactor would work, but remember to get torque it would need to use a turbine or motor mechanism which introduces inefficiencies. The device would have to generate enough acceleration to achieve escape velocity.

I brought up herbal petrol not as a strawman, but for the very fact it was debunked because it violated the conservation of mass.

Yes, if a society has a certain level of technical capability, you will have the development of new inventions. It has been in the west since the industrial age. We see it in India too where necessity is the mother of invention.

SriKumar
BRFite
Posts: 1577
Joined: 27 Feb 2006 07:22
Location: sarvatra

Re: Physics Thread.

Postby SriKumar » 18 Mar 2016 08:41

I have a question about more earthly stuff, literally and figuratively speaking. I am trying to understand how the 'Rashivalaya Yantra' in the Jaipur Jantar Mantar works, and more importantly: "How does one USE it to determine the position of sun in the zodiac constellation".

Background:
Rashivalaya yantra is a set of 12 sun-dial-like structures with a sloping 'staircase' (called gnomon) located in close proximity to each other. Their purpose (as I understand it) is to tell the location of the constellation in which the sun resides, at any time of the year. The question is: 'How do you use this set of 12 instruments to determine the constellation of sun'. See picture below of the Rashi-valaya yantra.

Image

What I could figure out based on internetting around:
There are 12 zodiac constellations (Leo, Scorpio, Libra etc. etc.) in the sky which form the backdrop of sun as the earth orbits around the sun. This means that the sun 'spends' roughly 1 month 'within' each of these constellations- as seen by a viewer on earth.

The problem is that one cannot see the constellation when the sun is on (too bright, even with sun shades), so ...enter the Rashivalaya yantra (RY).

The rashivalaya yantra has 12 'sub-yantras (see picture). Each of the 12 sub-yantras is a sun-dial unto itself. The sun will cast a shadow on each of the 12 RY sun-dials. There are 12 zodiac constellations, and 12 sub-yantras, with each sub-yantra associated with one constellation. One could posit that the sub-yantra which gets a perfectly aligned shadow at 'noon-time', the constellation associated with that specific sub-yantra is the constellation of the sun. This is at best a working hypothesis and not an explanation- there are several objections to this.

The sun will cast a 'perfectly aligned' shadow with the gnomon (the staircase like structure) with several sub-yantras in the course of a day- so which one is it? Is it when the sun is at the highest point in the sky during that day?

If so, how do we interpret the 'capricon' and 'cancer' yantras? They have the exactly same alignment (albeit different slopes for the gnomon- see below) and will definitely cast the same aligned shadow on their respective dials.

Also, the gnomon of each of the 12 sub-yantras has a different slope to it. What is the significance of this?

For the solar sun-dial i.e. samrat yantra, the gnomon is aligned at an angle equal to the latitude of Jaipur- 26 degrees. As I understand it, this slope allows the gnomon to cast a shadow on its dial which would move linearly with time i.e. the scale on the dial can be linear. I dont understand the need for a dial (the curved structure) in the 12 sub-yantras- so what additional information does the dial give?

If one had to instruct a 7th class kid- this is what you need to do to tell the constellation of the sun, what instructions would you give the kid. This instruction set is what I am trying to determine.

There is some explanations on the web but most of them relate to the construction of the devices. One report from N.Univ. Singapore has tried to figure this out, the students did a very commendable job, but I did not fully understand it. TIA.

A_Gupta
BRF Oldie
Posts: 10297
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 18 Mar 2016 10:10

Perhaps Ramanujan’s struggle to find an audience for his work and the hardship he underwent to be taken seriously by the mathematics establishment of his time informs Dr. Bhargava’s relatively tolerant take on the inclusion of sessions on ancient Indian science in the proceedings of the Indian Science Congress. Last year, an ex-pilot made the apocryphal claim that an ancient Indian sage had laid down detailed plans of ancient airplanes; this year, too, a bureaucrat successfully submitted in the environmental sciences sub-conference a ‘research paper’ on how Lord Shiva was a “great environmentalist” — though he didn’t go on to present it.

To Dr. Bhargava, this is “fringe” science, though he adds that it’s in the very nature of science congresses the world over to occasionally entertain speculative claims and “fringe” science. The key, according to him, is that fringe science be treated as such and not be given greater space than actual scientific discussions or talks. “I was upset at the last Congress [in Mumbai] that the fantastic achievements of the ISRO (Indian Space Research Organisation) were barely covered in the media and all space was taken up by those discussions. Real scientists there were wondering, ‘Hey, what about us?’” he says. Moreover, he adds, at the International Congress of Mathematicians (ICM), there were always claims that someone had solved the Riemann hypothesis [a bedevilling maths problem, nearly a century old, whose solving guarantees a million dollars in prize money from the Clay Mathematics Institute]. On the other hand, the solution to another tricky problem — of rapidly testing whether a given number was prime — was proffered by an Indian computer scientist, Manindra Agrawal and his two graduate students. “They are computer scientists and not professional mathematicians. Imagine if their work wasn’t accepted at an ICM… solutions can from anywhere,” he reasons, “Science marches ahead when as many ideas are allowed to be communicated.”


http://www.thehindu.com/opinion/manjul- ... 086197.ece

A_Gupta
BRF Oldie
Posts: 10297
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 18 Mar 2016 10:18

SriKumar wrote:The sun will cast a 'perfectly aligned' shadow with the gnomon (the staircase like structure) with several sub-yantras in the course of a day- so which one is it? Is it when the sun is at the highest point in the sky during that day?


It makes sense to use the sun at the highest point in the sky during that day, i.e., noon of the solar day. It is determinable without a highly accurate clock.

A_Gupta
BRF Oldie
Posts: 10297
Joined: 23 Oct 2001 11:31
Contact:

Re: Physics Thread.

Postby A_Gupta » 18 Mar 2016 10:21

SriKumar wrote:There are 12 zodiac constellations (Leo, Scorpio, Libra etc. etc.) in the sky which form the backdrop of sun as the earth orbits around the sun. This means that the sun 'spends' roughly 1 month 'within' each of these constellations- as seen by a viewer on earth.

The problem is that one cannot see the constellation when the sun is on (too bright, even with sun shades), so ...enter the Rashivalaya yantra (RY).


Sorry for the piece-meal attempts to answer the questions. Without such yantras, the constellation that the sun is in would be determined, e.g., by observation of the stars just before sun-rise.


Return to “Technology & Economic Forum”

Who is online

Users browsing this forum: No registered users and 17 guests