Physics Discussion Thread

[member_22733]

I was thinking about perpetual motion machines and one thought occurred to me: Humans have built them since late 1950s and they are all around us: They are called artificial satellites.

They are also victims of entropy in the long run, but if positioned correctly they can be "almost" perpetual!

[member_28108]

I was thinking about perpetual motion machines and one thought occurred to me: Humans have built them since late 1950s and they are all around us: They are called artificial satellites.

They are also victims of entropy in the long run, but if positioned correctly they can be "almost" perpetual!

The thing is not perpetual motion but generating useful energy more than what is put in.That is the crux.

[member_22733]

Of course, if you extract energy out of satellites they will fall out of the sky I was using "perpetual" in a very narrow sense of the term. They are perpetually in motion

[Vayutuvan]

LokeshC: I realized that the Continuum Mecahnics link doesn't realy answer your question about Langrangian. Since I may be entirely incorrect in my presumption of what you are after, let me give a few more references - all are Dover ppaerbacks and can be had for not more than 15 bucks each.

1. The Variational Principles of Mechanics - Cornelius Lanczos

I find this book to be the best in terms of coverage and clarity. Deals with classical, relativistic mechanics. Noethers principle is also talked about. Maxwells equations and EM is also dealt with.

A side tidbit is that Laczos invented wa tis called the Lanczos Eiegnvalue Algorithm an iterative algorithm that gives more and more lower eigenpairs as the number of iterations go forward. It is supposed to be one of the cleverest eigenpair algorithms SPD matrics. Usually these eigenpairs are used to approximate the behavior of sub-structure embedded in a larger structure in a hierarchical fashion to simulate problems which have hundreds of millions of degrees freedom since low eigenpairs have the maximum impact on the dynamics of a system.

2. Calculus of Variations - Gelfand and Fomin:

I quickly scanned and found it to be more mathematical (read more abstract) but still quite understandable. This is much smaller book than Lanczos (but could be harder to digest as all the math books are). Of course, Gelfand is quite a famous Russian mathematician. There is a chapter on optimal control.

3. Introduction to Applied Mathematics - Francis D. Murnaghan: I have read bits and pieces as on a need basis. This is an old book. I am not sure whether it is in print. But worth a try because Dover started re-issuing a lot of classics. I am not sure how good this book is as my reading was only in sections.

4. Mathematical Physics - Donald H. Menzel

See comments for number 3 above.

Non-dover (Wellesley Cambridge Press) and alomst surely out of print

Introduction to Applied Math by Gilbert Strang: This is a panaromic nook interlinking all the important Aplied Mathematics topics. The only problem is that it has a very conversational tone just like his Linear Algebra book. Some people likw it some people don't. While it is good as an overview, you need to look at the references for more formal treatment (Proposition, lemma, theorem, example, exercise). This bok has enough examples and touches on Linear Programming (both Simplex and Interior point are touched upon but not at any depth - only how or why they work - one would not be able to implement simplex or Interior point algorithms just fromthis book alone), network flows, duality, Lagrange multiplers, KKT conditions all dealt with and also connections physical systems (Elctrical networks, Fluids, Structures) is made.

I think if a quick read of Strang followed by Lanczos would be one possibility.

[member_22733]

Thanks matrimc garu!

Here is more info: Wave propagation along the mooring lines of large structures when (and if) they get loose. Some new type of mooring line designs have some slack built into them and it causes changes in the nature of waves that propagate up and down (can be caused due to currents, temperature differences etc). This impacts tolerance limits on the materials required to build it, which then means we need to go back to drawing board if we make mistakes .

Other than business reasons, I was really curious on how he managed to simulate (a part of) it. Lagrangian techniques were heavily used and hence my interest in them.

Other than 12th grade Newtonian (vector algebra) style physics, I never had heard of the energy-variation style reformulation.

[Amber G.]

x-post
May be of interest to a few hakim sahibs here in this thread.. specially after all this talk of GPS and navigation and things of that nature...

The noble prize in Medicine went for "discoverers of brain’s 'inner GPS'..and navigational system...

Also interesting is the fact - O'Keefe switched to Medicine in school, after jumping from subject to subject including aeronautics at college ...

[Bade]

http://www.slate.com/articles/health_an ... nobel.html

But this year's may go to one or more of the Neutrino Physicists.

[Vayutuvan]

No wonder women are not interested in physics. Just two woman Nobel laureates ever! Not saying that they should get even if not deserving. It might be a case of self fulfilling prophecy.

[Amber G.]

http://www.slate.com/articles/health_an ... nobel.html

But this year's may go to one or more of the Neutrino Physicists.

Nice article. This year's went to Blue LED ..(The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2014 to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura

Few comments/tidbits - Goeppert-Mayer’ visited IIT Kanpur where I first saw her. Mildred Dresselhaus, was my son's UG adviser.

Also, the list does not mention, people like Rosalyn Sussman Yalow, or Irene Curie whose work can easily be classified as in Physics.

Interesting that people like Lalitha Chandrasekhar (who was a very good Physicist, was a graduate student of C.V Raman), or Mayer above, while doing first class physics research, had no official position at U of Chicago, in those days - other than "wife" of a professor)--

[Bade]

Blue LED being selected is a total surprise. Did you have any hints to that AmberG ?

The next big one for particle physics anytime soon will have to do with Neutrino masses, which might also open up new insights to other areas begging an answer. SUSY models which I do not understand much about, seem to be going with nothing to show so far both at the Tevatron and LHC energy scales. Hints of mass to neutrinos (via oscillations) breaks the Standard Model assumptions, but no further peek give by nature to the human mind/machine.

It is sad that SSC was not built. So many years would not have been wasted in the SUSY searches, and Higgs would have been found too much earlier by the SSC.

[SaiK]

heard that on NPR todin morning drop to school that means we can get bright white light from LEDs now! (RGB)? wasn't blue LED already out in the market? is this work done long time back?

i think this will have great impacts on night lighting and products.

===

ps: ignore.. moorkh me.. i just read about it 20 years back! something was behind me telling i'm stupid.

[Bade]

Nobels are rarely given for recent work. I think in recent times the prize for Josephson Junction was an exception.

[Amber G.]

I had no idea or hint about Nobel going to LED before the announcement.

[SaiK]

http://www.frontline.in/science-and-tec ... epage=true

X-rays and Synchrotron
A national need

Much of the global efforts using X-rays are based on synchrotron radiation, and India has to depend on state-of-the-art facilities abroad. Therefore, setting up a new synchrotron must be seen as part of the larger national scientific endeavour. By M. VIJAYAN
THE United Nations has declared 2014 the Year of Crystallography. Diffraction of X-rays by crystals was discovered by Max von Laue and his colleagues at the University of Munich, Germany, in 1912, and 2012 marked the centenary of this discovery. The first structure that Lawrence Bragg determined using X-ray diffraction in 1913, marking the birth of X-ray crystallography, was that of sodium chloride. The year 2013 was celebrated as the centenary of this important event. These two centenary years are now followed by the U.N. Year of Crystallography.

The progress registered using X-ray diffraction during the past century has been truly spectacular. Much of what we know about the structure of matter has been revealed using X-ray crystallography. A large number of Nobel Prizes have been awarded for these efforts. The first structure to be determined using X-ray crystallography contained just two independent atoms. The biggest one, that of ribosome determined recently, an effort for which Venkatraman Ramakrishnan, Tom A. Steitz and Ada Yonath were awarded the Nobel Prize, contains a couple of hundred thousand atoms. That is a measure of the progress of X-ray crystallography in the past one hundred years.

India has a long and distinguished tradition in crystallography, starting with the pioneering efforts of K. Banerjee, a student of C.V. Raman, in Calcutta (now Kolkata) in the 1930s. The pioneers in the area in the country included G.N. Ramachandran and S. Ramaseshan, both students of Raman at the Indian Institute of Science (IISc) in Bangalore, and Ajit Ram Verma. Crystallographic research now constitutes an important component of the scientific efforts in India. It encompasses inorganic and organic chemistry, materials science and biology. X-ray spectroscopy also has grown hand in hand with crystallography. X-rays have other widespread industrial and medical applications, too. The most spectacular applications of X-ray crystallography in recent decades have been in the field of structural biology, which is concerned with the structure and structure-function relationships of biological macromolecules like proteins. These applications are often collectively referred to as macromolecular crystallography.

Technological advances have had a great effect on the progress of crystallography. For example, crystallographers were among the first scientists to take to computation. As far as macromolecular crystallography is concerned, it is often said that two “rings” contributed substantially to the progress of the field in recent years. One is the plasmid ring used in genetic engineering, which has enabled crystallographers to produce macromolecular samples in quantities sufficient for crystallisation through cloning. Cloning techniques also allow scientists to elucidate the roles of individual links in the protein chain through mutations of different kinds. These techniques, often collectively referred to as molecular biology techniques, are widely used in India. The second ring is the “synchrotron ring”. India is not in an enviable position in relation to this ring.

Pushing X-ray limits
Conventionally, X-rays are produced by bombarding an appropriate metallic target with fast electrons under high vacuum. However, only about 2 per cent of the energy of the electrons is converted into X-rays. The rest is converted into heat. Therefore, the target has to be continuously cooled. But cooling efficiency is limited. Consequently, the energy of the electrons and hence the flux of the X-rays produced cannot be arbitrarily increased. Rotating anode X-ray generators were developed to improve the intensity of X-rays. As the anode is constantly rotating, no region of it is continuously bombarded by electrons. The energy of the bombarding electrons can then be substantially increased, resulting in a higher-intensity X-ray beam. For logistical reasons, the size of the rotating anode cannot be arbitrarily increased. Therefore, there are limits to the intensities of X-rays produced by rotating anode generators. This is where things stood nearly half a century ago.

High energy physics involves the use of particle accelerators in which charged particles are accelerated to relativistic velocities, often in a circular path. Acceleration of charged particles results in the emission of electromagnetic radiation. It was the realisation that the intensity of this radiation from particle accelerators in the X-ray range could be very high that led to the development of synchrotron X-ray sources. A synchrotron source consists essentially of a circular “storage” ring, typically of a couple of hundred metres diameter, in which electrons are accelerated to relativistic velocities using magnets. High-speed electrons are initially injected into the storage ring using a “booster”. A synchrotron source produces a continuous spectrum of electromagnetic radiation. The peak of the intensity distribution is in the X-ray range when the energy of the electrons is in the gigaelectronvolt (GeV) range. The peak occurs in the soft X-ray/ultraviolet region when the energy is a few hundred mega-electronvolts (MeV). Unless stated otherwise, the word synchrotron often refers to storage rings with energies in the GeV range.


The intensity of X-rays produced by a synchrotron source is often several orders of magnitude higher than that of the radiation produced by the best rotating anode home sources. Conventional X-ray generators produce high intensities only at certain specified wavelengths determined by the electronic structure of the target material. A synchrotron source, on the other hand, produces radiation of a much higher intensity over a range of wavelengths. One can pick and choose any wavelength from this range. This “tunability” confers great advantage on synchrotron radiation. In what are called third-generation synchrotrons, “insertion devices” are also used to enhance the intensity of the radiation produced.

Yet another important beneficial property of synchrotron radiation is its small angular divergence. In a typical synchrotron ring, X-rays are tapped tangentially at dozens of locations around the periphery of the ring. “Beamlines” are set up at each of these locations to bring radiation to experimental stations. Thus, dozens of experiments are simultaneously performed on a synchrotron facility.

A synchrotron source is a truly multipurpose facility. The beneficial properties of synchrotron radiation make it an ideal tool for a variety of applications in widely different fields. Much of the spectacular applications in macromolecular crystallography have been made possible through the use of synchrotron facilities. This is substantially true of other areas of crystallography as well. Materials science is another area in which the facilities are extensively used. Spectroscopic experiments of different kinds are successfully conducted using synchrotron radiation. Synchrotron facilities have added a new dimension to the medical and industrial uses of X-rays.

Globally, synchrotrons began to be operative in the 1970s. There are now close to 50 synchrotron facilities operating in different parts of the world, including in countries like China, Brazil and South Korea. Even Thailand has a small one. Many countries have more than one synchrotron facility. Much of the global efforts using X-rays are now based on synchrotron radiation.

Efforts in India
Discussions on synchrotron facilities in India started in the late 1970s. The most definitive meeting on the subject took place in 1984 at the Bhabha Atomic Research Centre (BARC), Mumbai. At the meeting, P.K. Iyengar represented the Department of Atomic Energy (DAE), S. Varadarajan the Department of Science and Technology (DST), and Rais Ahmed the University Grants Commission (UGC). Many of us potential users also participated in the meeting. It was decided in that meeting that the DAE would undertake to construct simultaneously a low-energy Indus-1, which is of limited use, and a high-energy Indus-2, which is what most of us were concerned with. The hope then was that the facilities would become available within a reasonable time frame. Work on the facilities began at the Centre for Advanced Technology (CAT), Indore, which was subsequently rechristened Raja Ramanna Centre for Advanced Technology (RRCAT), in 1986. The 450 MeV Indus-1 was commissioned in 1999.


The main machine, Indus-2, did not appear to be anywhere near the horizon at that time. In the meantime, efforts that depended on synchrotron facilities gathered momentum in the country. Macromolecular crystallography came of age by the turn of the century. Organised efforts in materials science spread to different parts of the country. There were also other areas that could benefit through the use of synchrotron facilities. In response to the increasing need for synchrotron radiation, the DST made some arrangements for Indian scientists to access facilities abroad such as Elettra in Italy. These arrangements, though welcome, were inadequate to meet the growing requirements in India. They were in no way a substitute to having such facilities in India. Therefore, the user community began to grow restive. That resulted in a meeting of representative synchrotron users in Hyderabad in 2004, convened by Seyed E. Hasnain, the then Director of the Centre for DNA Fingerprinting and Diagnostics (CDFD), and Kota Harinarayana, the then Vice-Chancellor of the University of Hyderabad, with Shekhar Mande, then at CDFD, as the main organiser. This writer was asked to chair the meeting.

The Hyderabad meeting recommended the setting up of a new synchrotron facility in addition to expediting the work at the RRCAT. R. Chidambaram, Principal Scientific Adviser (PSA) to the Government of India, and Vinod Sahni, the then Director of the RRCAT, were kept informed about the deliberations of the Hyderabad meeting. Subsequently, some of us visited the RRCAT and had detailed discussions with Sahni and his colleagues. That was the beginning of extensive interactions between the user community and colleagues at the RRCAT. That also gave an additional fillip to the work on Indus-2.

By now, synchrotron facilities had become a topic of active discussion in the scientific community. The issue figured in the 2006 report of the Steering Committee on Science and Technology for the Eleventh Five-Year Plan. A major recommendation of the committee, which was implemented, was to lease/set up beamlines in synchrotron facilities abroad. In pursuance of this recommendation, a materials science beamline was set up at Photon Factory, Tsukuba, Japan, with funds from the DST. The Department of Biotechnology (DBT) funded part-leasing of the macromolecular beamline BM14 at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The DST made a contribution to the setting up of Petra at Hamburg, Germany, for assured Indian access to the facility. It also funded the setting up of a macromolecular crystallography/high-pressure beamline with partial Indian ownership at Elettra. These beamlines have certainly raised the synchrotron-based efforts in India to a higher level.

Indus-2

In 2009, P. Balaram, the then Director of the IISc, proposed the setting up of a synchrotron facility at its newly acquired land in Chitradurga. The proposal was discussed at a meeting of the Scientific Advisory Committee to the Cabinet (SAC-C) in August 2009. Soon afterwards, the PSA constituted a Committee of Experts, with S.K. Sikka, formerly of the BARC, and this writer as co-chairmen, with a broad mandate on synchrotron facilities. It considered a proposal submitted by D.D. Sarma, on behalf of the IISc, to set up a 3 GeV synchrotron. Another proposal, for a 6 GeV machine, was submitted by Milan Sanyal, the then Director of the Saha Institute of Nuclear Physics (SINP), Kolkata. The SAC-C commended both the proposals to the Planning Commission.

In the meantime, work on Indus-2 at the RRCAT, now headed by P.D. Gupta, was progressing well with the full support and encouragement of the Committee of Experts referred to above. It is difficult to pinpoint the exact period during which it became operational, as the work went through several stages. In any case, it was ready for reasonably trouble-free data collection by 2012-13. That was an achievement to rejoice in. India had at last its own operational synchrotron source.

Indus-2 can be described as a second-generation synchrotron. Most of the well-known sources around the world are third-generation machines. Therefore, it is not a state-of-the-art facility. However, it has been a great technology demonstrator. The experience gained from constructing it will stand us in good stead. Many scientists have already profitably used Indus-2 for their research. However, that does not obviate the need for a state-of-the-art Indian synchrotron source. The DAE itself recognised this need in 2013. Later that year, the Scientific Advisory Committee to the Prime Minister (SAC-PM) also recommended the setting up of a new facility. Subsequently, in March this year, a meeting at the Planning Commission chaired by K. Kasturirangan endorsed the proposal for a new facility.

The national dimension
Thus, a broad consensus on the need for a state-of-the-art Indian synchrotron facility exists. The question is how to translate this consensus into reality. In my view, a synchrotron facility has a national dimension that transcends the requirement of the users for powerful X-ray beams with appropriate properties. A major problem with the Indian economy is the weakness of the manufacturing sector. This weakness is partly due to the inadequacy of instrumentation capability in the civilian sector. Competence of a high order in instrumentation exists in the strategic sector involving the DAE, the Department of Space (DoS) and the Defence Research and Development Organisation (DRDO). By the very nature of the strategic sector, this competence cannot easily percolate into the public domain.


On the other hand, the non-strategic sector is relatively open. However, most research and educational institutions in the country in the non-strategic sector are bereft of any significant instrumentation capability. One way of building up this capability across the board is for institutions in the strategic and the non-strategic sectors to undertake mega projects jointly. Synchrotron facilities lend themselves to such joint efforts. One is certainly likely to encounter turf problems as well as institutional and individual egos. With sustained efforts these problems can be overcome.

Synchrotron technology and the science based on it are developing continuously. Setting up a synchrotron facility is not a one-off process. Development in the area needs to be pursued continuously. Therefore, the setting up of a new synchrotron facility should be looked upon as one step in a continuous process. A given synchrotron facility is used simultaneously by workers belonging to widely different disciplines and it is an ideal medium for promoting multidisciplinary interactions. Thus, the move to set up a new Indian synchrotron facility should be looked upon not only as an effort to provide beamlines for individual groups of users but also as part of a larger national endeavour.

A consensus has been reached only on the need for a new synchrotron source in the country. Still, there is no clarity as to who will take up the responsibility. The location is yet to be decided. The specifications are yet to be worked out. Then, of course, there is the major issue of funding. As was suggested at the meeting at the Planning Commission referred to earlier, deliberations on these issues should be initiated jointly by the DAE and the DST or, more generally, the Ministry of Science and Technology. Currently, the DAE is the only agency that has hands-on experience in setting up a synchrotron facility. However, the stakeholders are mostly those who do research using grants from the departments under the Ministry of Science and Technology.

The DAE and the DST have a long tradition of working together and they should have no difficulty in spearheading the synchrotron effort together. That would also enable the strategic and the non-strategic sectors. In due course, other strategic and non-strategic agencies should also be brought into the deliberations. Irrespective of which agency/agencies or institution(s) incubate it, eventually the new synchrotron facility should be an autonomous entity. In the context of India’s overall scientific performance and in relation to the global situation, India has lagged behind in its synchrotron efforts. The earlier it move towards a state-of-the-art Indian synchrotron, the better it will be.

M. Vijayan is INSA Albert Einstein Research Professor, Molecular Biophysics Unit, Indian Institute of Science, Bangalore.

[SaiK]

http://blogs.scientificamerican.com/obs ... -security/
What It’s Like to Carry Your Nobel Prize through Airport Security

Your life does change overnight,” recalled astrophysicist Brian Schmidt, who won the 2011 Nobel Physics Prize for co-discovering dark energy—the mysterious element of the universe that is causing the expansion of spacetime to speed up. “It’s not like you get advanced warning, they just sort of call you up, in my case, in the middle of cooking dinner. ‘Hello? By the way, you’ve won the Nobel Prize.’”

“When I won this, my grandma, who lives in Fargo, North Dakota, wanted to see it. I was coming around so I decided I’d bring my Nobel Prize. You would think that carrying around a Nobel Prize would be uneventful, and it was uneventful, until I tried to leave Fargo with it, and went through the X-ray machine. I could see they were puzzled. It was in my laptop bag. It’s made of gold, so it absorbs all the X-rays—it’s completely black. And they had never seen anything completely black.

“They’re like, ‘Sir, there’s something in your bag.’
I said, ‘Yes, I think it’s this box.’
They said, ‘What’s in the box?’
I said, ‘a large gold medal,’ as one does.
So they opened it up and they said, ‘What’s it made out of?’
I said, ‘gold.’
And they’re like, ‘Uhhhh. Who gave this to you?’
‘The King of Sweden.’
‘Why did he give this to you?’
‘Because I helped discover the expansion rate of the universe was accelerating.’
At which point, they were beginning to lose their sense of humor. I explained to them it was a Nobel Prize, and their main question was, ‘Why were you in Fargo?’”

[Bade]

Track Cosmic Rays with Smartphone Apps.

http://www.scientificamerican.com/podca ... phone-app/

Physicists don’t know for sure where cosmic rays come from, but they suspect supernovae and powerful black holes are involved. Although we’re bombarded with the particles, the very highest energy cosmic rays are rare. Studying them has therefore been difficult. But it turns out that smartphone cameras are actually good at detecting them.

When these especially energetic rays hit Earth’s atmosphere they create a shower of other charged particles. These particles hit a camera’s sensor, resulting in one bright pixel against a dark background. If enough phones in the same area see particles, scientists can recreate the cosmic ray’s path through space.

You can take part in the project through an app called CRAYFIS (for Cosmic Rays Found in Smartphones). [Daniel Whiteson et al, Observing Ultra-High Energy Cosmic Rays with Smartphones]

[Yayavar]

Intriguing. I was wondering how one would know what to look for and share the info - this is not there in the linked article. Turns out they have written a CRAYFIS app; and one can read the paper here http://crayfis.ps.uci.edu/

[SaiK]

http://timesofindia.indiatimes.com/home ... 577152.cms

something to irk our fizzic friends here

[gakakkad]

http://timesofindia.indiatimes.com/home ... 577152.cms

something to irk our fizzic friends here

god..toilet is projecting cern like bcci...

[Amber G.]

http://timesofindia.indiatimes.com/home ... 577152.cms

something to irk our fizzic friends here

".

..Pakistan-beats-India-in-race-to-become-Cern-associate-member..

Along with India, Pakistan also "beats" Japan, Russia, Canada and the USA.. (Who have same status of "membership" as India..)... What a dorky ddm..

BTW..Some one should put a headline in Paki newspaper(s)... Israel was the latest "member".. a "status" above Pak's "associate member"

[rsingh]

Saw intersteller yesterday. Hoa come there was a planet near the blackhole(right on the edge of horizon) and and was auitable for life? Secondly there was foam on the waves in sea which was devoid of organic life.

[member_22733]

That is because of the peculiar nature of the blackhole : It rotates at near light speed, so it has a gravimetric drag frame-drag that "rotates" the surrounding space time which counter-acts with the pull of the blackhole (or some such complicated thing). But its mathematically feasible and has been accepted in peer-reviewed physics papers.

Also some blackholes (supermassive blackholes especially) can shine brighter than many many million stars. Stars obey the Eddington Limit (i.e. the limit where the radiation pressure == gravitational pull). Black holes dont obey that limit because of almost infinite gravity.

The foam is an interesting loophole, however can not organic molecules themselves cause foam?, they set out searching for planets with potential to harbor life so presence of organic molecules is a big plus. Disclaimer: Neither a biologist nor a physicist.

Here is another loophole (I think) that I found in the movie (xpost from Nukkad):

One plot hole that I found in Interstellar was that it ignored the "red shift" phenomena. i.e. the "ocean planet" that they landed initially where "signals were still coming from" is hokum.

The landing craft was destroyed a few minutes after landing (due to enormous tidal waves miles high) but it kept sending the beacon signals, that much is physically plausible. But it gets slightly implausible after that : since the time slows down on the planet surface (1 hour on the surface == 7 years on a gravitation free field), it would have "red shifted" the radio signals that were sent from the planet.

I.e. lets say there was a 1kHz beacon that was beamed off the planet :- it would have been received as a 1/(613200) kHz. The unless the receiver was tuned to receive it, they would have missed the signal. BTW: 613200 is approx number of hours in 7 years.

Basically thats what happens when you fall into a black hole, whatever signals (i.e. energy ) that holds you together (i.e. your information content) gets red-shifted to approach zero. But before you reach 0 redshift the black hole evaporates due to Hawking radiation. Before you reach the center of the Black hole the universe would have gone into heat death and the blackhole itself would have evaporated (scattering you into subatomic particles in the process).

[SaiK]

how the heck cooper jumps into singularity, and wakes up at an haspataal at satrun's earth station. 125 years!?

also, they show the worm hole entrance very close to saturn. so the wormhole and blackhole are close by to the solar system?

[gakakkad]

>>also, they show the worm hole entrance very close to saturn. so the wormhole and blackhole are close by to the solar system?
nearest black holes are several thousand light years away...(thankfully) ..there is no observational or experimental evidence to prove existence of a wormhole...presently they exist theoretically onlee...

[SaiK]

understood, but theoretically how can those planets in the solar system -i.e, saturn, uranus, neptune and pluto would not have got sucked into the worm hole at some orbital point. or was this wormhole on 90* azimuth to orbital plane?

ps: may be the wormhole is only for worms!

[SaiK]

http://fouriestseries.tumblr.com/post/8 ... al-systems

The Lagrangian points are the five locations in an orbital system where the combined gravitational force of two large masses is exactly canceled out by the centrifugal force arising from the rotating reference frame.

At these five points, the net force on a third body (of negligible mass) is 0, allowing the third object to be completely stationary relative to the two other masses. That is, when placed at any of these points, the third body stays perfectly still in the rotating frame.

interesting!

[SaiK]

Sterile Neutrinos Still Theoretical
Seven-month long neutrino experiment finds no signs of the rumored sterile neutrino
http://www.scientificamerican.com/artic ... SA_Twitter

[Amber G.]

From the GDF's physics dhaga -

Amazing stuff. Anyone know how it works? All the write-ups are very vague other than calling it a magnetic effect.

<youtube link of the hovercraft>

Amazing indeed. It won one of Time magazine's 25 Best Inventions of 2014, and fun to see. They also has a "white box" which you can order and play with I assume to see how it works

Physics of the above (Hendo Hoverboard) is easy, the engineering/technological aspect is the one which is challenging.

I am replying the physics related stuff in T&E forum's Physics thread for general interest.

Explaining it in a simpler but accurate way -

Basically, known since Faraday - if there are two coils, and if an alternating current is passed in one coil, there is an induced current, again alternating, in the other coil, and this will cause a repulsion between the two coils. Now the other "coil/loop" can be replaced with a metal plate (It must be non-ferromagnetic - like copper). - It is as simple as that.

In theory if the Hoverboard, has coils/loops (called the "four" engines) with large alternating current, and the bottom sheet (ground) is copper. The technological challenge is to produce such a large current (and high frequency) with batteries.

For perspective, when one demonstrates this in a typical physics UG lab, the typical current needs to be a few hundred amperes, very high frequency to lift a Kg of metal plate. The induced current makes the the plate hot unless one deals with super conductor. This is why, this kind of "levitation" is a very popular demonstration when one is showing super conductors. The difference for the hovercraft is that the current flows in coils on the hover craft and ground is copper plate.

The following youtube explains the above physics part and hopefully of the interest.


There are other ways, fairly well known and easy to understand physic wise, to levitate (for example using diagrammatic materials etc.

Added later, I looked at the original patent for the above. Looks like instead of large current in coil, they are using rotating permanent magnets..Here is all the details if some one is interested..
Patent

[Amber G.]

May be of interest ... (and may not be known to many - I always had fun teaching this while teaching Electricity-magnetism physics theory)

Magnetic levitation, (a stable magnetic levitation), if you have strong enough magnets (IOW super conducting ones) and some diamagnetic material... and creativity to use them properly.

Of course, human body is a diamagnetic material so, if you get a strong enough magnet you can levitate!

(At present, for demo, we can only use frogs )
For those who are interested the basic physics theory, Here is one paper from Applied Physics Journal :Diamagnetic levitation: Flying frogs and floating magnets

[Neshant]

Lifter technology has been known since the 1920s.

Passing a very high voltage through some aluminum foil craft causes the craft to take off looking like anti-gravity.

Supposedly its caused by ion wind or something. Pretty interesting stuff.

[rsingh]

We know evaporation cools the surface but why?

[member_22733]

For a liquid to evaporate, there must be transfer of heat from somewhere, it is usually obtained from the surface that the liquid sits on thus cooling the surface down. The surface must necessarily be at a higher temperature than the boiling point of the "coolant" liquid.

Ignore the djinn phyjigs above.

[member_22733]

That said, ablative cooling is the one that i am a little confused about . Dont completely understand the thermodynamics of that one.

Added later: Appears that I dont understand evaporative cooling either. There is a hole in my understanding of Thermodynamics

[johneeG]

It seems to me that motion and energy are interlinked. So, whenever there is any motion, there seems to be some kind of energy. Whenever there is any energy, there seems to be some kind of motion. I don't think its possible to create motion without energy or to create energy without motion.

So, when and how did this cycle of energy and motion start? Because they seem to be interdependent. I mean, one needs energy for motion and one needs motion for energy. If energy always existed, it means motion also must always exist, isn't it? So, what kind of energy and motion existed when the universe came into being?

[Amber G.]

We know evaporation cools the surface but why?

Physics does not answer "Why".. but FWIW, hope the following adds to little more physics understanding...

1. Heat (as we understand from Kinetic Energy of Heat) is nothing but the Kinetic Energy of atoms (or molecules - which is nothing but group of atoms). For gas, on one hand, each molecule is free to roam (there is little interaction between molecules as they are far away from each other) and (1/2 mv^2) is KE.
The solids on the other hand, the molecules just vibrate with fixed mean positions. Liquid is some where in the middle, molecules can move but there is interaction between two molecules.. etc..

2. Heat is *average* KE... some molecules are fast (higher energy) some are slow...When two molecules collide (or come near each other) they exchange energy.. (faster molecule becomes slower and slower molecule become faster).. the average energy (in close system) remain the same. (For perspective, the typical velocity of an air molecule at room temperature (or water for that matter in an ocean ) is of the order of thousands of Km/Hr)

3. If a solid (surface) is wet the KE of water and surface molecule on average is equal (they are at the same temperature). (The argument is same, if you have a cup of water, and water "evaporates" from liquid surface).

4. If a water molecule leaves (it evaporates).. normally it means it has higher energy (moving faster than average) so when it leaves, the average energy of surface is now less than what it was before.
(Some thing akin to - if a few richer people leave a group - the group (on average) is now poorer)

(The critical part: in water, there are some faster (than average) molecules.. if they come close to surface, the attractive force of other molecules is not able to prevent them from "leaving" the water body..- they are now water vapor escaped in the atmosphere..water (on average) becomes cooler.. the air above becomes warmer..)
Hope this helps.

[SriKumar]

A follow-up question.....if there is a layer of water over a flat surface, e.g. say someone pours a cup of water on stone surface; Assume air, water and the stone surface are all at the same temperature (30 C, say). Would we expect the water to evaporate?

I'd say, 'yes' even though the air and water are at the same temperature (but the degree of evaporation would depend on the humidity of air). In the process of this vaporization, can we expect the temperature of the stone surface (on which this water was poured on) to reduce...i.e. can it go below 30 C? If the answer is yes, it seems to suggest that heat flowed from a cooler surface to warmer surface. If the answer is 'no', the question is 'can evaporation take place with no change in temperature of the substrate'?

Following are some relevant observations: (i) if one sprinkles water on a surface and it evaporates, the area feels cooler after some time. (ii) Water stored in a desi matka (earthen pot) is definitely cooler than water in a glass/cup, and this, as I understand, is due to the evaporation of water from the matka surface....(so some capillary effect is also at work here).

[member_22733]

^^^ I was thinking of that too (after I posted by djinn ideas yesterday): What conditions are needed for evaporative cooling to work properly (low humidity is one of them), and how can heat flow from a "cooler object" to a hotter object (2nd law of thermodynamics)?

Question to ask is: What are the reservoirs here and what is the "work done"? The surface is the "hotter reservoir", but what I am confused about is the cooler reservoir: is it the vapor of the evaporating material, or the air around in general ?

[Vayutuvan]

In my experience, the cooling (reduction in temperature) is directly proportional the surface area of the evaporating water.

[Vayutuvan]

Only if there is air circulation that is moving the water vapour away form the surface will be there cooling, right? Else the air would get saturated and no evaporation.

[member_22733]

^^^ Yes, thats why I hate humid areas. I sweat like a monster and it takes forever to dry up. I was not designed to be in Humid areas.