matthen:

If a mathematician wants to cross a road, they will think carefully about their optimal path. The total distance of the path should be minimised, but they prefer walking on the sidewalk to the road. If there is no extra discomfort from being on the road, the best path is a straight line, but as it increases it is better to cross the road more directly.  The resulting path is exactly the same as a ray of light refracting through a block of glass [with relative refractive index equal to the ratio of these ‘discomfort levels’]. Fermat’s principle says that light will want to spend less time in the glass (on the road), as it actually travels more slowly in the glass. [video] [code] [more]

distant-traveller:

Question: If 2 black holes get near each other, can they then gravitationally pull matter out of the other black hole & back into “normal” space?

The short answer is no.

A black hole (in the traditional sense) is defined as an object that has collapsed so that its radius is equal to, or less than, the Schwarzschild of the object.

What does this mean?

Every object has a Schwarzschild radius; this is the point at which an object’s mass is so compressed that the gravitational influence overpowers the other forces of nature and it collapses to a singularity.

Of course, not every object is massive enough to collapse to its Schwarzschild radius. The Earth’s Schwarzschild radius, for example, is about the diameter of a small marble. If you were to apply enough energy to the Earth and compress its mass to that size, it would collapse to form a black hole. The same is true for humans, except I’d need to compress you to a point some 10-million times smaller than a marble in order to turn you into a black hole.

So, what is special about the Schwarzschild radius? This is the point at which the escape velocity for the object is equal to the speed of light. Obviously, since you can’t travel ,or faster than, the speed of light you can’t get out of a black hole neither can another black hole pull you out.

It’s important to realize that, outside of the Schwarzschild radius (also known as the event horizon), spacetime is normal. You can interact with a black hole in the same ways you interact with any other object of mass.

Image credit: NASA/CXC/A.Hobart

Article: From Quarks to Quasars

(via science-in-a-jar)

vicen7e:

Carl Sagan’s The Cosmos S1E1

(via science-in-a-jar)

(Source: nokogo, via space-tart)

thescienceofreality:

This Week in Science - May 13 - 19, 2013:

• Magnetar at black hole here.
• Cloned human stem cells here.
• Cell calculators here.
• Music matched to color here.
• Scientists agreeing on climate change here.
• Remote-piloted plane here.
• Earth’s core here.
• Bright lunar explosion here.
• American asteroid sampling here.
• Hofstadter butterfly effect here.
• Electric shocks aid math skills here.
• Printable solar panels here.

(via science-in-a-jar)

thatscienceguy:

This is a simulation of a rotating 4 dimensional Cube, otherwise known as a Tesseract.

What you are seeing is it Rotating. It is not being distorted, reshaped, or anything like that. it is simply Rotating - It appears to be distorted because you are only seeing the ‘projection’ of it. similarly if you rotated a 3D cube infront of lamp the shadow you would see would appear to distort.

(via science-in-a-jar)

carbonstuff:

Let’s talk about the dark night. Yes this post is about Batman.

Our common assumption is that the night sky is supposed to be dark with only few dots of light.

But then, aren’t there supposed to billions upon billions of stars in the night sky emitting light. Yes, they are very far away, but, there is nothing stopping (like air or glass) the light from reaching us. So, shouldn’t all those stars make the night sky (very) bright and not dark ?

This is actually called Olbers’ Paradox. 

Let’s look at the problem in another way. We can divide the universe into a series of concentric shells, being 5 light years thick. Thus, a certain number of stars will be in the shell 1,00,000 to 1,00,005 light years away. If the universe is homogeneous at a large scale (i.e., static), then there would be four times as many stars in a second shell between 2,00,000 to 2,00,005 light years away.

But, the second shell is twice as far away, so each star in it would appear four times dimmer than the first shell (intensity is inversely proportional to the square of distance). Thus the total light received from the second shell is the same as the total light received from the first shell.

Thus, the argument is that if the universe were static and filled infinitely with stars, the night sky should be much brighter than it is now.

I think you guessed the loop hole here. I said if the universe were static, which it clearly isn’t.

The Big Bang explains this paradox by saying that the universe started at a point, and expanded from that point. Thus, it is not static.

We know that the expansion is accelerating. So, two things happen. 

One is that, those stars in the night sky are moving away from us and the distance between them and us increases. This increase the time for to see them and eventually it takes millions of years for the light from those stars to reach us.

Second, which is the more important reason, is that these starts get redshifted away. Redshifting is when the wavelength of an object moving away from us goes towards the red side of the spectrum and eventually, it goes into the infra red, which we cannot see. It is like we listen to a honking truck passing by at great speed. As it moves away from us, the the sound becomes softer and softer and eventually it is inaudible.

So, because of these reasons, we never get to experience the real night sky light. But, it may be a good thing, as otherwise our eyes would be blinded by the light !

Image via Wikimedia Commons

(via science-junkie)