Physics Discussion Thread

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rsingh
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Re: Physics Thread.

Postby rsingh » 10 Aug 2015 18:08

ArmenT wrote:
rsingh wrote:What happens if you put two bullet in the gun(assuming it is possible) one after another. You fire the gun. First bullet fires the second. Doest it mean that second bullet has double vilocity then the first one?

I see that others have posted a lot of theoretical replies above as to what would happen in this scenario, but allow me to put a bit of practical reality into this:

The situation where there is a bullet in the barrel and a second one is loaded behind it is often caused by what is known as a squib load. If you are ever in this situation, NEVER fire that second cartridge. Why? At best, you may suffer a bulged barrel, at worst, there is a good chance of the gun barrel exploding and injuring yourself and those around you. See the above link for details.

Physics: it's all fun in theory, until someone loses an eye.[/quot

C'est pour ca je dit ......assuming it is possible

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Re: Physics Thread.

Postby Amber G. » 10 Aug 2015 19:11

Interesting note which may apply to some discussion here.. The note is by R. Allain ( I think) I saw recently somewhere..
>>>
Learning Physics Is Tough. Get Used to It

In recent courses, I have noticed two troubling practices of physics students. The first is the student response to homework problems. I hear the following kind of statements all too often:

Oh, you are stuck on homework problem number 13? I found a solution on YouTube. That helped a lot. Just Google it, you can find all the solutions.


The second problem is partially my fault. When I give an in-class assessment, I leave the solution out on the front desk so that students can check their answers when they are finished. Instead of studying this and figuring out their mistakes, students will usually just take a quick picture of the solutions using their phone. Of course they ask if it’s OK to take a snapshot first, and I let them. However, the problem is that they think of the solution as something to collect rather than something to learn from.

Here is the most important lesson for physics students (and really all students). The learning process is difficult. If learning was easy they would call it pie (as easy as pie—although I don’t really understand that line). If a student is doing homework or studying and there is no struggle, there is no learning. Without confusion, the student either already understood it or never tried. This comes back to my favorite line:

Confusion is the sweat of learning.


You can’t just google a physics solution and expect to learn. Imagine if Luke Skywalker had access to the Internet on Dagobah. Here’s what would have happened when his x-wing sunk beneath the water.

Yoda: So certain are you? Always with you what cannot be done. Do you nothing that I say?

Luke: Master moving stones around is one thing, but this is entirely different. But let me just Google “how to lift an x-wing with the Force.” Ah. Here it is.


Of course that’s not what happened .... Yes, students learn physics by working on problems and by failing to solve problems. It’s the journey to the solution that’s important, not the solution itself. Using a video solution would be like using a golf cart to run 5 miles. Sure, you end up in the same place if you run or ride—but they do not produce the same results.

But why do students think this? Why do they think learning is as simple as quick search or a photo with their smart phone? There are likely many reasons for students to hold these learning beliefs. However, I popular media often doesn’t help. Remember this scene from The Avengers?

SHIELD agent Maria Hill asks Tony Stark: “When did you become an expert in thermonuclear astrophysics?” Stark’s answer: “Last night”. This shows that Tony Stark is so awesome he just figured astrophysics out last night. Clearly, students feel that you have to be a special superhero to understand astrophysics. You either get it in one night, or you’ll never get it. I would prefer to have Stark say “Well, I’ve been working in this field for 10 years and I’m just scratching the surface.” Maybe that wouldn’t fit too well in the movie.


Or here’s another good one from Days of Thunder.

Cole pulls up to the race track to test out a stock car.

Harry Hogge: What do you know about stock car racing?

Cole Trickle: Well… watched it on television, of course.

Harry Hogge: You’ve seen it on television?

Cole Trickle: ESPN. The coverage is excellent, you’d be surprised at how much you can pick up.

Harry Hogge: I’m sure I would.

See. Learning is simple. You just need to watch some videos and you’ll be all set—except when you aren’t. Nope. Learning is tough, but it’s totally worth it.

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Re: Physics Thread.

Postby rsingh » 11 Aug 2015 20:03

What do you think of this
https://www.youtube.com/watch?v=GeyDf4ooPdo

It seems to defy gravity.

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Re: Physics Thread.

Postby Amber G. » 12 Aug 2015 01:14

Very Nice!!

rsingh wrote:What do you think of this
https://www.youtube.com/watch?v=GeyDf4ooPdo

It seems to defy gravity.

Except that, of course, it doesn't.

And these kind of experiment are worth performing. And they have been (or ought to be) part of good introductory course in physics for as far back I can remember. (They can be easily rigged, using a bicycle wheel is what I have often seen). I have seen this in quite a few science centers/museums (and they have been favorite of mine whenever I took kids to visit museum).

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Re: Physics Thread.

Postby Multatuli » 19 Sep 2015 11:18

Ultrathin 'Invisibility Cloak' Can Match Any Background

http://www.livescience.com/52216-ultrat ... cloak.html

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Re: Physics Thread.

Postby Amber G. » 06 Oct 2015 21:26

Some brf physics profs may be happy (I hope old brfite still lurks here)..

So atmospheric neutrino oscillations have their Nobel prize! Congrats to Kajita and McDonald.

The Nobel Prize in Physics 2015

You may enjoy the audio of the telephone call.

https://soundcloud.com/nobelprize/i-gave-my-wife-a-hug-arthur-b-mcdonald-on-being-awarded-the-nobel-prize

The other phone call is at https://soundcloud.com/nobelprize/kind-of-unbelievable-takaaki-kajita-on-being-awarded-the-nobel-prize

And the interview:
[url]http://www.nobelprize.org/…/la…/2015/mcdonald-interview.html[/url]

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Re: Physics Thread.

Postby kenop » 13 Nov 2015 05:18

Dark Matter Proof/Clues?
“WHEN you have eliminated the impossible, whatever remains, no matter how improbable, must be the truth.” Though that maxim of Sherlock Holmes would rarely withstand scrutiny in the everyday world, where facts can be fuzzy and the truth is often protean, it is not a bad one for fundamental physics—a field where there really is only one right answer. It has certainly been the approach taken by Dan Hooper and Lisa Goodenough, two hunters of some of physics’s most elusive creatures: the particles of which dark matter is composed. They think they have eliminated all alternative explanations to these particles being the origin of a powerful clutch of gamma rays that come from the centre of the Milky Way, the Earth’s home galaxy, and they have been saying so for several years.

This week the chief remaining group of sceptics—the team that runs the satellite which detected the gamma rays in question—has thrown in the towel and agreed that it, too, can come up with no convincing alternative. Though this concession does not, quite, close the “Case of the missing WIMPS”, it will require a considerable reversal of fortune for Dr Hooper and Dr Goodenough now to be proved wrong.

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Re: Physics Thread.

Postby Amber G. » 05 Dec 2015 23:48

This is about a month old news, but since no one posted it here.. I am posting it.
Amber G. wrote:Some brf physics profs may be happy (I hope old brfite still lurks here)..

So atmospheric neutrino oscillations have their Nobel prize! Congrats to Kajita and McDonald.

The Nobel Prize in Physics 2015..

McDonald (along with several of his colleagues) also got 2016 Breakthrough Prize in Fundamental Physics ($3 million - more money than a Nobel) for investigating neutrino oscillation...

What may be more interesting for brf janta is that a name (or two :) ) of the "co-winners" may be more than familiar to some. Let me congratulate..

The announcement was made about a month ago, but since no one has posted the news I am doing it now. It is not that often that one get informed by a Facebook friend that "hey I may have won something" in a FB post. I think it is also neat to see that smaller collaborators are recognized for their achievements.. and the prize money being shared.

(For those who are not familiar, it is fairly common in high energy physics papers to have hundreds co-authors -- It is some what rare when 100's of odd co-authors are also recognized)
Members of T2K Collaboration awarded Breakthrough Prize
Last edited by Amber G. on 06 Dec 2015 00:12, edited 1 time in total.

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Re: Physics Thread.

Postby Satya_anveshi » 06 Dec 2015 00:06

Congratulations! Knowing Guru ji's interest in Bharat, I can't imagine guru ji is not lurking (particularly when the other blogger's real mukhota is out'ted in full glory for what it is).

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Re: Physics Thread.

Postby SaiK » 07 Dec 2015 00:06

normally I post these in GDF.. trying out here.

http://blogs.scientificamerican.com/dar ... -machines/

Confirmed: Black Holes are Magnetism-Powered Eating Machines

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Re: Physics Thread.

Postby TSJones » 11 Dec 2015 12:46

you say you want some gold?

why sure, we'll whip some up for ya......

https://astronomynow.com/2015/12/09/gam ... -elements/

This was witnessed in 2013 by astronomers led by Edo Berger of the Harvard–Smithsonian Center for Astrophysics in Massachusetts who, after observing the afterglow of the short gamma-ray burst GRB 130603B, estimated that it had produced ten times the mass of the Moon in terms of gold alone.
:eek:

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Re: Physics Thread.

Postby Amber G. » 11 Dec 2015 23:37

TSJones wrote:

why sure, we'll whip some up for ya......
.. GRB 130603B, estimated that it had produced ten times the mass of the Moon in terms of gold alone.


I am sure you know that, some say (remember the movie Space odyssey 2010), Jupiter's core is pure diamond of the size of earth..but until that claim is proved positively, AFAIK the biggest actual diamond ever discovered in our galaxy is a BPM 37093, (constellation Centaurus and only 50 light years from Earth - Credit to ravis Metcalfe/Ruth Bazinet, Harvard-Smithsonian Center for Astrophysics).. of the size of moon, not quite the size of earth but 10,000,000,000,000,000,000,000,000,000,000,000 carats..

(Of course, in our own solar system -- per some Caltech scientist, Uranus and Neptune, are hiding, beneath their dense atmosphere, oceans of liquid diamond, in which float solid diamond icebergs!)



Meanwhile down on earth a few tidbits you may already know:

- In 1940's in Los Alamos lab a guy, had a pure gold hemisphere of the size of soccer ball as a door stopper -- no body paid any attention to it -- no extra security. This was one of the least expensive stuff in the room, not worthy enough to occupy a self space. The self space was occupied by other elements of the periodical table. They were testing all elements for cross-section-area wrt to neutron scattering. ..

- Around the same time in Oak Ridge, the physicists wanted lot of copper wire for windings for the strong electromagnets (to separate U235 using giant mass spectrometers). Due to war copper was very difficult to get. So some one had a bright idea and asked US treasury (mint) if they can borrow some silver. Silver is even better conductor than copper. US treasury did have lot of silver for coins and asked how much they want. The answer was "only about 16,000 metric tons". US treasury told them, "we measure silver in troy ounces, not in metric tons" :-o
(BTW US treasury did provide 16,000 tons to Oak Ridge. After the war, all the coils were melted down and *all* silver was returned to US treasury :) )

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Re: Physics Thread.

Postby Bade » 12 Dec 2015 03:15

AmberG, thanks for pointing out the nuance in Dysons's statement. He is an excellent physicist no doubt and there is always the chance of a misinterpretation from short statements from anyone.

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Re: Physics Thread.

Postby Vayutuvan » 13 Dec 2015 11:46

Physics gurus: what do you make of prof. Ranga-ram chary of caltech's claim that his group measured hotspots in CMB radiation which points to parallel universes? Those universes could have a different fine structure constant tha the universe we - as in we humans - inhabit.

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Re: Physics Thread.

Postby Amber G. » 15 Dec 2015 20:58


Bade
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Re: Physics Thread.

Postby Bade » 17 Dec 2015 09:15

There is some buzz around this....but I have no first hand info from people in the business...
http://www.scientificamerican.com/article/potential-new-particle-shows-up-at-the-lhc-thrilling-and-confounding-physicists1/
From its signature at the LHC, the particle must weigh roughly 750 giga-electron volts (GeV), around 750 times the mass of the proton, and would fall into the class of bosons, meaning its spin has an integer value. Some theorists say the newcomer looks like a heavier cousin of the Higgs boson, which similarly first showed up at the LHC as a highly intriguing blip in the data about four years ago. Or it could be a kind of portal particle into the dark matter sector—because this particle decays almost immediately, on its own it cannot account for the invisible matter that seems to be ubiquitous in space, but it may be a messenger that communicates with the dark matter particle, theorists suggested. Another hypothetical alternative is that it is a graviton, the predicted carrier particle for the force of gravity.

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Re: Physics Thread.

Postby Amber G. » 17 Dec 2015 22:20


Bade
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Re: Physics Thread.

Postby Bade » 18 Dec 2015 01:02

This one has a better description of the situation.

http://arstechnica.com/science/2015/12/ ... gravitons/

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Re: Physics Thread.

Postby Vayutuvan » 18 Dec 2015 03:54

Gravitons - does that mean gravity is quantized?

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Re: Physics Thread.

Postby negi » 18 Dec 2015 08:35

Well my understanding is if one uses Quantum mechanics to explain any physical phenomenon then all force fields have to be quantized , to be brutally honest it is a convenient hypothesis too as the concept of dual nature can then be applied to explain things rather more convincingly.

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Re: Physics Thread.

Postby Bade » 18 Dec 2015 09:09

To unify all forces, gravity "needs" to be quantized. But there is no functioning theory where Quantum Mechanics and Gravity meets. No experimental proof for gravitons yet too. Wiki has a simple write up on it.

Look for massless (not massive) spin-2 particles...then you have a graviton candidate.

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Re: Physics Thread.

Postby Bade » 18 Dec 2015 22:28


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Re: Physics Thread.

Postby rsingh » 25 Dec 2015 19:10

What is Fire ? I did some research where they say it is plasma made up of hot gases. Wood is mostly cellulose. cellulose molecule makes chain where is fixed by other molecules. So when we burn wood these intermolecular and intramolecular bond are broken and energy is released. C is left alone in the form of ash. Is there anything else to it?

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Re: Physics Thread.

Postby Prem Kumar » 27 Dec 2015 05:22

Bade wrote:To unify all forces, gravity "needs" to be quantized. But there is no functioning theory where Quantum Mechanics and Gravity meets. No experimental proof for gravitons yet too. Wiki has a simple write up on it.

Look for massless (not massive) spin-2 particles...then you have a graviton candidate.


Something I don't understand in the "quantization of gravity" approach. Einstein's theory has "background independence" - i.e. no dependence on coordinate systems. Space, time & mass are intertwined. QM on the other hand, required a background. Space & time don't "emerge" out of QM.

So, even if a graviton is to be found, how to explain say, the curvature of space-time by the presence of mass?

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Re: Physics Thread.

Postby Vayutuvan » 27 Dec 2015 05:32

ECG has a theory of time being quantized as well. I am not all that familiar with all this hi funda Physics to make out what that means or what do the Gravitons mean. That said, is mass quantized or not? Since one cannot find quarks other than as part of a fundamental particle, all of which have mass even neutrinos, mass is quantized, i.e. mass is not continuous. Or is it?

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Re: Physics Thread.

Postby TSJones » 27 Dec 2015 06:42

if you are thinking classically that space is separate entity, a void, then according to one theory that is an error.

accordingly, space is filled with energy/particles that continuously pop in and out of existence.

there is enough of this energy in a liter size jar of space to boil off the Pacific ocean in a few seconds.

IOWs, the whole universe is a mass energy/particle field.

that's a theory anyway.

but it does help to explain a few things.

also please remember, this universe can change itself depending upon your perspective or as Einstein has taught to us, "reference frame".

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Re: Physics Thread.

Postby Bade » 27 Dec 2015 07:22

Here is a nice write-up from one of the current masters of the field...

http://arxiv.org/pdf/gr-qc/0004005v1.pdf

http://cgpg.gravity.psu.edu/people/Asht ... icles.html

Specifically this from Ashtekar is short and lucid.
http://cgpg.gravity.psu.edu/people/Asht ... ndtime.pdf

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Re: Physics Thread.

Postby Vayutuvan » 27 Dec 2015 11:32

Bade thanks. Heard of Ashtekar. Syrvey/explanation papers are always interesting (for me), especially in an area which is a mystery.

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Re: Physics Thread.

Postby Amber G. » 27 Dec 2015 20:59

VT et all - Can gravity be quantized? I posted it before, but posting it again.. Enjoy.
Bohemian Gravity!

One of my favorite from Tim Blais -- a theoretical physicsist and a student of Alex Maloney.

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Re: Physics Thread.

Postby Vayutuvan » 27 Dec 2015 22:58

Video is nice. But I think one needs a passing knowledge of String Theory - what is a kahler manifold? - to understand the song.

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Re: Physics Thread.

Postby Amber G. » 07 Jan 2016 20:23

This could be very significant for India, in managing nuclear waste or production of heavy water (probably reducing cost to produce heavy water by 10x in very near future - the process is more efficient than any other I know of)
Graphene sieves deuterium from hydrogen
The researchers’ measurements show that graphene and boron nitride exhibit an isotope enrichment factor of about 10 for heavy water mixed with normal water. That is in contrast to the Girdler sulfide process, which has an enrichment factor of about two to three, up to 10 for electrolysis or a little over one for distillation. The preference of the graphene and boron-nitride sieves for hydrogen over deuterium is thought to be due to hydrogen’s greater vibrational energy, which allows it to ‘jump’ over the materials’ energy barriers.



Details in Science paper: http://www.sciencemag.org/content/351/6268/68.abstract?sid=c37a0d9d-1c5c-4c8e-98d3-4f70950a0e57

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Re: Physics Thread.

Postby Vayutuvan » 09 Jan 2016 00:44

From Physics World: These are a list of popular Physics books.
Book of the Year 2015

It's been another fine year for physics books, which makes it tough to pick just one as Physics World's Book of the Year 2015. Listen as we discuss a few of our favourites from the 10-strong shortlist and announce our choice of the year's finest popular-physics book


Shortlist for Physics World's Book of the Year 2015 (alphabetical by author)
  • Life on the Edge: the Coming of Age of Quantum Biology Jim Al-Khalili and Johnjoe McFadden
  • Physics on Your Feet: Ninety Minutes of Shame but a PhD for the Rest of Your Life Dmitry Budker and Alexander Sushkov
  • Half-Life: the Divided Life of Bruno Pontecorvo, Physicist or Spy Frank Close
  • Trespassing on Einstein's Lawn: a Father, a Daughter, the Meaning of Nothing and the Beginning of Everything Amanda Gefter
  • Beyond: Our Future in Space Chris Impey
  • The Water Book: the Extraordinary Story of Our Most Ordinary Substance Alok Jha
  • Monsters: the Hindenburg Disaster and the Birth of Pathological Technology Ed Regis
  • Tunnel Visions: the Rise and Fall of the Superconducting Super Collider Michael Riordan, Lillian Hoddeson, Adrienne Kolb
  • The Copernicus Complex: the Quest for our Cosmic (In)Significance Caleb Scharf
  • Atoms Under the Floorboards: the Surprising Science Hidden in Your Home Chris Woodford

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Re: Physics Thread.

Postby member_29058 » 13 Jan 2016 01:08

http://www.sciencedaily.com/releases/20 ... 144845.htm
Dirt-cheap catalyst may lower fuel costs for hydrogen-powered cars
'Green' process relies on sunlight

Sandia National Laboratories researchers seeking to make hydrogen a less expensive fuel for cars have upgraded a catalyst nearly as cheap as dirt -- molybdenum disulfide, "molly" for short -- to stand in for platinum, a rare element with the moonlike price of $1,500 a gram.

Sandia-induced changes elevate the plentiful, 37-cents-a-gram molly from being a welterweight outsider in the energy-catalyst field -- put crudely, a lazy bum that never amounted to much -- to a possible contender with the heavyweight champ.

The improved catalyst, expected to be the subject of an Oct. 7 Nature Communications paper, has already released four times the amount of hydrogen ever produced by molly from water.

To Sandia postdoctoral fellow and lead author Stan Chou, this is just the beginning: "We should get far more output as we learn to better integrate molly with, for example, fuel-cell systems," he said.

An additional benefit is that molly's action can be triggered by sunlight, a feature which eventually may provide users an off-the-grid means of securing hydrogen fuel.

Hydrogen fuel is desirable because, unlike gasoline, it doesn't release carbon into the atmosphere when burned. The combustion of hydrogen with oxygen produces an exhaust of only water.


But here's the rub: While the edges of these nanostructures match platinum in their ability to catalyze hydrogen, the relative immense surface area of their sliding interiors are useless because their molecular arrangements are different from their edges. Because of this excess baggage, a commercial catalyst would require a huge amount of molly. The slender edges would work hard like Cinderella, but the stepsister interiors would just hang out, doing nothing.

Chou, who works on two-dimensional materials and their properties, thought the intent should be to get these stepsisters jobs.


"Why Stan's work is impactful is that there was so much confusion as to how this process works and what structures are actually formed," said Kaehr. "He unambiguously showed that this desirable catalytic form is the end result of the completed reaction."

Said Sandia Fellow and University of New Mexico professor Jeff Brinker, another paper author, "People want a non-platinum catalyst. Molly is dirt cheap and abundant. By making these relatively enormous surface areas catalytically active, Stan established understanding of the structural relation of these two-dimensional materials that will determine how they will be used in the long run. You have to basically understand the material before you can move forward in changing industrial use."

Kaehr cautions that what's been established is a fundamental proof of principle, not an industrial process. "Water splitting is a challenging reaction. It can be poisoned, stopping the molly reaction after some time period. Then you can restart it with acid. There are many intricacies to be worked out.

"But getting inexpensive molly to work this much more efficiently could drive hydrogen production costs way down."

'Green' inorganic photosynthesis

Not requiring electricity to prompt the reaction may be convenient in some circumstances and also keep costs down.

"A molly catalyst is essentially a 'green' technology," said Chou. "We used sunlight for the experiment's motive power. The light is processed through a dye, which harvests the light. A photocatalytic process stores that energy in the chemical bonds of the liberated hydrogen molecule.

"It's a kind of photosynthesis, but using inorganic materials rather than plants," Chou continued. "Plants use enzymes powered by sunlight to break up water into hydrogen and oxygen in a delicate process. We're proposing a similar thing here, but in a more rapid reaction and with sturdier components."

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Re: Physics Thread.

Postby member_28638 » 13 Jan 2016 20:47

Scientists struggle to stay grounded after possible gravitational wave signal

http://www.theguardian.com/science/2016 ... ed-science


Why is this famous physicist tweeting rumors about gravitational waves?


https://www.washingtonpost.com/news/spe ... nal-waves/


Scientists may have just discovered Einstein’s gravitational waves

https://www.rt.com/news/328632-ripples- ... -einstein/

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Re: Physics Thread.

Postby Amber G. » 12 Feb 2016 06:06

Some pretty big physics news today ...
http://physics.aps.org/articles/v9/17
https://www.youtube.com/watch?v=n5Ycv2yYNG8
Scientists make first direct detection of gravitational waves
^^^ From MIT tech news writeup >>>

Almost 100 years ago today, Albert Einstein predicted the existence of gravitational waves — ripples in the fabric of space-time that are set off by extremely violent, cosmic cataclysms in the early universe. With his knowledge of the universe and the technology available in 1916, Einstein assumed that such ripples would be “vanishingly small” and nearly impossible to detect. The astronomical discoveries and technological advances over the past century have changed those prospects.

Now for the first time, scientists in the LIGO Scientific Collaboration — with a prominent role played by researchers at MIT and Caltech — have directly observed the ripples of gravitational waves in an instrument on Earth. In so doing, they have again dramatically confirmed Einstein’s theory of general relativity and opened up a new way in which to view the universe.

But there’s more: The scientists have also decoded the gravitational wave signal and determined its source. According to their calculations, the gravitational wave is the product of a collision between two massive black holes, 1.3 billion light years away — a remarkably extreme event that has not been observed until now.

The researchers detected the signal with the Laser Interferometer Gravitational-wave Observatory (LIGO) — twin detectors carefully constructed to detect incredibly tiny vibrations from passing gravitational waves. Once the researchers obtained a gravitational signal, they converted it into audio waves and listened to the sound of two black holes spiraling together, then merging into a larger single black hole.

“We’re actually hearing them go thump in the night,” says Matthew Evans, an assistant professor of physics at MIT. “We’re getting a signal which arrives at Earth, and we can put it on a speaker, and we can hear these black holes go, ‘Whoop.’ There’s a very visceral connection to this observation. You’re really listening to these things which before were somehow fantastic.”

By further analyzing the gravitational signal, the team was able to trace the final milliseconds before the black holes collided. They determined that the black holes, 30 times as massive as our sun, circled each other at close to the speed of light before fusing in a collision and giving off an enormous amount of energy equivalent to about three solar masses — according to Einstein’s equation E=mc2 — in the form of gravitational waves.

“Most of that energy is released in just a few tenths of a second,” says Peter Fritschel, LIGO’s chief detector scientist and a senior research scientist at MIT’s Kavli Institute for Astrophysics and Space Research. “For a very short amount of time, the actual power in gravitational waves was higher than all the light in the visible universe.”

These waves then rippled through the universe, effectively warping the fabric of space-time, before passing through Earth more than a billion years later as faint traces of their former, violent origins.

“It’s a spectacular signal,” says Rainer Weiss, a professor emeritus of physics at MIT. “It’s a signal many of us have wanted to observe since the time LIGO was proposed. It shows the dynamics of objects in the strongest gravitational fields imaginable, a domain where Newton’s gravity doesn’t work at all, and one needs the fully non-linear Einstein field equations to explain the phenomena. The triumph is that the waveform we measure is very well-represented by solutions of these equations. Einstein is right in a regime where his theory has never been tested before.”

The new results are published today in the journal Physical Review Letters.

“Magnificently in alignment”

The first evidence for gravitational waves came in 1974, when physicists Russell Hulse and Joseph Taylor discovered a pair of neutron stars, 21,000 light years from Earth, that seemed to behave in a curious pattern. They deduced that the stars were orbiting each other in such a way that they must be losing energy in the form of gravitational waves — a detection that earned the researchers the Nobel Prize in physics in 1993.

Now LIGO has made the first direct observation of gravitational waves with an instrument on Earth. The researchers detected the gravitational waves on September 14, 2015, at 5:51 a.m. EDT, using the twin LIGO interferometers, located in Livingston, Louisiana and Hanford, Washington.

Each L-shaped interferometer spans 4 kilometers in length and uses laser light split into two beams that travel back and forth through each arm, bouncing between precisely configured mirrors. Each beam monitors the distance between these mirrors, which, according to Einstein’s theory, will change infinitesimally when a gravitational wave passes by the instrument.

“You can almost visualize it as if you dropped a rock on the surface of a pond, and the ripple goes out,” says Nergis Malvalvala, the Curtis and Kathleen Marble Professor of Astrophysics at MIT. “[It’s] something that distorts the space time around it, and that distortion propagates outward and reaches us on Earth, hundreds of millions of light years later.”

Last March, researchers completed major upgrades to the interferometers, known as Advanced LIGO, increasing the instruments’ sensitivity and enabling them to detect a change in the length of each arm, smaller than one-ten-thousandth the diameter of a proton. By September, they were ready to start observing with them.

“The effect we’re measuring on Earth is equivalent to measuring the distance to the closest star, Alpha Centauri, to within a few microns,” Evans says. “It’s a very tough measurement to make. Einstein expected this to never have been pulled off.”

Nevertheless, a signal came through. Using Einstein’s equations, the team analyzed the signal and determined that it originated from a collision between two massive black holes.

“We thought it was going to be a huge challenge to prove to ourselves and others that the first few signals that we saw were not just flukes and random noise,” says David Shoemaker, director of the MIT LIGO Laboratory. “But nature was just unbelievably kind in delivering to us a signal that’s very large, extremely easy to understand, and absolutely, magnificently in alignment with Einstein’s theory.”

For LIGO’s hundreds of scientists, this new detection of gravitational waves marks not only a culmination of a decades-long search, but also the beginning of a new way to look at the universe.

“This really opens up a whole new area for astrophysics,” Evans says. “We always look to the sky with telescopes and look for electromagnetic radiation like light, radio waves, or X-rays. Now gravitational waves are a completely new way in which we can get to know the universe around us.”

Tiny detection, massive payoff

LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of some 950 scientists at universities around the United States, including MIT, and in 15 other countries. The LIGO Observatories are operated by MIT and Caltech. The instruments were first explored as a means to detect gravitational waves in the 1970s by Weiss, who along with Kip Thorne and Ronald Drever from Caltech proposed LIGO in the 1980s.

“This has been 20 years of work, and for some of us, even more,” Evans says. “It’s been a long time working on these detectors, without seeing anything. So it’s a real sea change and an interesting psychological change for the whole collaboration.”

“The project represents a triumph for federally funded research,” says Maria Zuber, vice president for research and E. A. Griswold Professor of Geophysics at MIT. “LIGO is an example of a high-risk, high-return investment in discovery-driven science. In this case the investment was major and sustained over many years, with a successful outcome far from assured. But the scientific payoff is shaping up to be extraordinary. While the discoveries reported here are already magnificent, they represent the tip of the iceberg of what will be learned about fundamental physics and the nature of the universe.”

The LIGO Observatories are due for more upgrades in the near future. Currently, the instruments are performing at one-third of their projected sensitivity. Once they are fully optimized, Shoemaker predicts that scientists will be able to detect gravitational waves emanating “from the edge of the universe.”

“In a few years, when this is fully commissioned, we should be seeing events from a whole variety of objects: black holes, neutron stars, supernova, as well as things we haven’t imagined yet, on the frequency of once a day or once a week, depending on how many surprises are out there.” Shoemaker says. “That’s our dream, and so far we don’t have any reason to know that that’s not true.”

As for this new gravitational signal, Weiss, who first came up with the rudimentary design for LIGO in the 1970s as part of an experimental exercise for one of his MIT courses, sees the tiny detection as a massive payoff.

“This is the first real evidence that we’ve seen now of high-gravitational field strengths: monstrous things like stars, moving at the velocity of light, smashing into each other and making the geometry of space-time turn into some sort of washing machine,” Weiss says. “And this horrendously strong thing made a very tiny effect in our apparatus, a relative motion of 10 to the minus 18 meters between the mirrors in the interferometer arms. It’s sort of unbelievable to think about.”

This research was funded by the National Science Foundation.

Amber G.
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Re: Physics Thread.

Postby Amber G. » 12 Feb 2016 08:06

^^^ On India's contribution .. tweet from PM Modi
Hope to move forward to make even bigger contribution with an advanced gravitational wave detector in the country.

https://twitter.com/narendramodi/status/697809783445856258?ref_src=twsrc%5Etfw

deejay
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Re: Physics Thread.

Postby deejay » 12 Feb 2016 08:46

Thank you for the report on the Gravitational Field announcements Amber G. Was following it yesterday.

Amber G.
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Re: Physics Thread.

Postby Amber G. » 12 Feb 2016 20:34

^^^ Thank you. I am glad that this was helpful.

I am posting the PRL article, for those who might be interested but do not have access. An article in PRL generally has a 5 page limit but in this case they let if go and allowed more than 5 pages.
https://dl.dropboxusercontent.com/u/18133796/PhysRevLett.116.061102%20%281%29.pdf

SriKumar
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Re: Physics Thread.

Postby SriKumar » 13 Feb 2016 03:55

Some general questions on this topic:

1. Are these gravitational waves the same that which causes the force of gravity between masses? Or are these a different kind of gravity waves.

2. The principle for detection is (as I understand it) interference of light, producing dark patches if they interfere destructively, or a bright spot if they interfere constructively. The interference is caused by a difference in distance traversed by the 2 light beams. How is such a sensitive apparatus (which can detect displacements of 10e-18 m) not be vulnerable to vibrations from various sources e.g. from within earth's crust (vibrations from plate movements for example).

3. Can this apparatus detect changes in gravitational forces due to, say, planets moving around the solar system over time as they revolve?

4. How do they calibrate an instrument like this i.e. what is a 'resting' state where it is deemed to be free of gravitational influences, or atleast, in some sort of an equilibrium?

disha
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Re: Physics Thread.

Postby disha » 13 Feb 2016 08:50

Status of Third LIGO in India.

https://dcc.ligo.org/public/0075/M1100296/002/LIGO-India_lw-v2.pdf

Significant contribution from Indians.


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