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Prasanna Bhogale
Works at Universität zu Köln
Attends University Of Cologne
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Prasanna Bhogale

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awesomeness with +Nima Doroud !!
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yes please !
 
This is a campaign to get Google+ to support the LaTeX markup language for the purpose of posting to the stream.

1) From your home page click on the gear icon in the top right corner
2) Choose 'Send Feedback'
3) Type in something to the affect of "Please support LaTeX on Google+"
4) Drag the dialog box over your stream and click 'Submit'
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Prasanna Bhogale

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why ?
just, why ?
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Hmph!  Why did I watch this video? 
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this is so cool. 
Why did I not study planetary/solar system science again ?
 
Jupiter and the Sun are the two largest objects in our Solar System, and as they orbit around one another, they create regions where their gravity roughly cancels out. These are the Lagrangian points, created whenever two objects orbit one another: places where gravity is such that another small object can follow along in the orbit without being pulled in or out. And since things aren't getting pulled out of there, they get stuck in there as well: and so we have two large clumps of asteroids (and miscellaneous smaller space debris) in Jupiter's orbit. These are called the Trojan Asteroids; the group ahead of Jupiter is known as the Greek Camp, and the group behind it the Trojan Camp, with the asteroids in each camp being named after famous people in that war. Together, these two camps have as many asteroids as the Asteroid Belt.

Other stable patterns are possible, too: another one is what's called a 3:2 resonance pattern, asteroids whose motion gets confined to a basically triangular shape by the combined pull of Jupiter and the Sun. This group (for Jupiter) is called the Hilda Family, and their route forms a triangle with its three points at the two Lagrange points and at the point on Jupiter's orbit directly opposite it from the Sun. 

None of these orbits are perfectly stable, because each of these asteroids is subject to pulling from everything in the Solar System; as a result, an asteroid can shift from the Lagrange points to the Hilda family, and from the Hilda family to the Asteroid Belt (not shown), especially if it runs into something and changes its course. 

The reason that Pluto was demoted from planet to dwarf planet is that we realized that these things are not only numerous, but some of them are quite big. Some things we formerly called asteroids are actually bigger than Pluto, so the naming started to seem a little silly. So our Solar System has, in decreasing order of size, four gas giant planets (Jupiter, Saturn, Neptune and Uranus); four rocky planets (Earth, Venus, Mars, and Mercury); five officially recognized dwarf planets (Eris, Pluto, Haumea, Makemake, and Ceres); and a tremendous number of asteroids. (We suspect that there are actually about 100 dwarf planets, but the job of classifying what's an asteroid and what's actually a planet is still in progress -- see the "dwarf planet" link below if you want to know the details)

Ceres orbits in the Asteroid Belt, about halfway between Mars and Jupiter, just inside the triangle of the Hilda Family; Pluto and Haumea are both in the distant Kuiper Belt, outside the orbit of Neptune but shepherded by its orbit in much the same way that the Hildas are shepherded by Jupiter; Makemake is what's called a "cubewano," living in the Kuiper Belt but unshepherded, orbiting independently; and Eris is part of the Scattered Disc, the even more distant objects whose orbits don't sit nicely in the plane of the Solar System at all, having been kicked out of that plane by (we believe) scattering off large bodies like Jupiter.

But mostly, I wanted to share this to show you how things orbit. This picture comes from the amazing archive at http://sajri.astronomy.cz/asteroidgroups/groups.htm, which has many other such pictures, and comes to me via +Max Rubenacker

More information about all of these things:
http://en.wikipedia.org/wiki/Lagrangian_point
http://en.wikipedia.org/wiki/Trojan_(astronomy)
http://en.wikipedia.org/wiki/Hilda_family
http://en.wikipedia.org/wiki/Dwarf_planet
http://en.wikipedia.org/wiki/Kuiper_belt
http://en.wikipedia.org/wiki/Scattered_disc

#ScienceEveryDay
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look at Jupiter ... its like a Big Daddy watching all the kids play
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Prasanna Bhogale

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super cool stuff... a black hole is a LOT bigger on the inside than on the outside.
 
Black holes - bigger on the inside

Guess what: black holes are bigger inside than they look - and they get bigger as they get older! 

For example, take the big black hole in the center of our galaxy, called Sagittarius A*.  It's about 2 million kilometers across.  That's pretty big - but the orbit of Mercury is 60 times bigger.  This black hole is old, roughly a billion years old.  And here's the cool part:  it's been growing on the inside  all this time!  

How is this possible?  Well, since spacetime is severely warped in a black hole, its volume can be bigger than you'd guess from outside.  And its volume can change.  Since we understand general relativity quite well, we can calculate how this works!  But nobody thought of doing it until last year, when Marios Christodoulou and my friend Carlo Rovelli did it.   

How big is the black hole at the center of our galaxy?  On the inside, it can hold a million solar systems!  Its volume is about 10^34 cubic kilometers!   And it's growing at a rate of about 10^25 cubic kilometers per year!

Or suppose you have an ordinary star that turns into a black hole.  This black hole will last a long time before it evaporates due to Hawking radiation.  Christodolou and Rovelli estimate how big its volume will get before this happens.  And it gets really big - bigger than the current-day observable universe!

Before you get too excited, remember: people falling into the black hole will not have time to do anything fun inside.  They will hit the singularity in a short time.  Very very roughly speaking, the problem is not the shortage of space inside the black hole, it's the shortage of time.  

If you fall into the black hole at the center of our galaxy, it will be about 1 minute, at most, before you hit the singularity.   You will not get to see most of the space inside the black hole!   The singularity is not in the 'middle' of the black hole - it's in your future.  You will hit it before you can reach the 'middle'.  So, you will only get to see part of the 'edge regions' inside the black hole.

The 'middle regions' can only be seen by people who fell in much earlier.  And they can't see the 'edge', where you are!

And now for the serious part. 

The hard part of this problem is defining the volume inside a black hole. 

If you choose a moment in time, the black hole's event horizon at that moment is a sphere.  There are infinitely many ways to extend this sphere to a solid ball.  In other words: there are many ways to choose a slice of space inside the black hole whose boundary is your chosen sphere. 

The slice can bend forwards in time, or backwards in time.  We can choose a wiggly slice or a smooth one.  Each slice has its own volume.  

How do you choose one, so you can calculate its volume? Christodoulou and Rovelli choose the one with the largest volume. This may sound like it's cheating.  But it's not.

Think of a simpler problem one dimension down.  You have a loop of wire.  You ask me: "What's the area of the surface whose boundary is this loop?" 

I say: "That's a meaningless question!  Which surface?  There are lots!"  

You say: "Pick the best one!"

So, it's up to me.   I take some soapy water and make a soap film whose boundary is that loop.  That's the surface I use.   If the loop of wire is not too crazy in its shape, this surface is uniquely defined.   In some sense it's the "least wiggly" surface I could choose.

This surface minimizes the area.  A more wiggly surface would have more area.

Christodoulou and Rovelli are doing the same thing.  But spacetime is different than space!   If you choose a wiggly 3-dimensional spatial surface in spacetime, it will have less volume than a flatter surface with the same boundary!  

So, the way to pick the flattest, nicest spatial surface inside our black hole is to pick the one that maximizes the volume. 

If you tried to minimize the volume, you could get it as close to zero as you wanted.  And this would have nothing to do with black holes!   This would be true even in your living room.

Puzzle: why?

Here's the paper:

• Marios Christodoulou and Carlo Rovelli, How big is a black hole?, http://arxiv.org/abs/1411.2854.

#spnetwork arXiv:1441.2854 #generalRelativity  
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this. is. brilliant. 
Van Gogh, you beauty. 
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One expects a space research organization to be less parochial.
 
Statement regarding suspension of some NASA activities with Russian Government representatives:

Given Russia's ongoing violation of Ukraine's sovereignty and territorial integrity, NASA is suspending the majority of its ongoing engagements with the Russian Federation.  NASA and Roscosmos will, however, continue to work together to maintain safe and continuous operation of the International Space Station. NASA is laser focused on a plan to return human spaceflight launches to American soil, and end our reliance on Russia to get into space.  This has been a top priority of the Obama Administration’s for the past five years, and had our plan been fully funded, we would have returned American human spaceflight launches – and the jobs they support – back to the United States next year.  With the reduced level of funding approved by Congress, we’re now looking at launching from U.S. soil in 2017.  The choice here is between fully funding the plan to bring space launches back to America or continuing to send millions of dollars to the Russians.  It’s that simple.  The Obama Administration chooses to invest in America – and we are hopeful that Congress will do the same.
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Yes.
 
Doesn’t the stuff you keep online deserve the same protection as the stuff you keep offline? Under a law called ECPA, government agencies in the U.S. can see what you’ve written and stored online without a warrant. Sign this petition to the White House and tell the government to get a warrant!
http://goo.gl/ecAjrS 
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Have him in circles
408 people
Sushma Kulkarni's profile photo
suthar suresh's profile photo
Sai krishna's profile photo
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Marta Luksza's profile photo
Sanjay bhat's profile photo
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  • Universität zu Köln
    PhD research, present
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An observer of humanity and the universe.
Education
  • University Of Cologne
    Theoretical Physics - phd, 2010 - present
  • U. Waterloo/Perimeter Institute of theoretical Physics - PSI
    Theoretical Physics, 2009 - 2010
  • University of St. Andrews
    Photonics, 2008 - 2009
  • Universiteit Gent
    Photonics, 2007 - 2008
  • Vrij Universiteit Brussel
    Photonics, 2008 - 2008
  • NITK - Surathkal
    Electronics and Communication, 2003 - 2007
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