Relativity

Geometry / Mathematics / Physics / etc.

General Relativity is the Curvature of Spacetime

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Einstein rings are awesome!

Figure 1 shows light from a distant blue galaxy that is distorted into a so-called Einstein ring by the curvature of spacetime around a red galaxy. This is called gravitational lensing and today we’ll learn how it works. This is part three of my many-part series on general relativity. Last time, I told you how general relativity is the dynamics of distance, which we know is a consequence of the fact that gravity is the same as acceleration. This time, I describe the consequences of the fact gravity warps distance. And in the process, we’ll learn precisely why gravity

Physics / Relativity / Science And Math

General Relativity is the Dynamics of Distance

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kogler crazy art installation

This is part two in a many-part series on general relativity. Last time, I described how Galileo almost discovered general relativity. In particular, I told you that gravity isn’t a force. In fact, gravity is the same as acceleration. Now, this is a completely crazy idea. After all, we’re all sitting in the gravitational field of the Earth right now, but we don’t feel like we’re moving, let alone accelerating. But let’s take this crazy idea at face value and see where it leads us. (Of course, the Earth is spinning, which is an acceleration. And it’s orbiting the sun,

Physics / Relativity / Science And Math

Galileo Almost Discovered General Relativity

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Hipster Galileo

We all know the (probably apocryphal) story. Galileo Galilei, all around physics bad-ass, went up to the top of Leaning Tower of Pisa and dropped stuff off the top. He found that objects of vastly different weights, like bowling balls and feathers for example, would fall at exactly the same rate and hit the ground at exactly the same time. Air resistance gets in the way, of course. But if you perform the experiment in vacuum, as these guys did, then you do find the bowling ball and the feather land at exactly the same time: This leads to

Astrophysics / Geometry / Mathematics / etc.

Speculative Sunday: Can a Black Hole Explode?

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Cassiopeia A Spitzer Image

Nothing can escape the gravitational pull of a black hole, not even light. That’s why they’re, well, black. (Of course, as I’ve described before, black holes can glow very brightly, thanks to all the in-falling matter. Sometimes they even produce gamma rays. I’m also ignoring the negligible amount of Hawking radiation that black holes theoretically produce.) Once you pass the event horizon of a black hole, you cannot ever escape. Escape is simply forbidden by the laws of physics. That is, of course…if there actually is an event horizon, not just something that looks like one. Carlo Rovelli ,

Astrophysics / Physics / Relativity

The Curvature of Spacetime

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Abell 2218

Spacetime is curved. We’ve all heard the line. But what does it mean? Well on the largest scales, the curvature of spacetime is abundantly clear as the warped fabric of the universe distorts images of distant objects. The image below is of the Abell 2218 galaxy cluster, taken by the Hubble Space Telescope. The cluster is very massive so it warps the spacetime around it. This warped spacetime acts as a lens so that light light coming from galaxies behind Abell 2218 is spread out much more than it should be. The result is that images of galaxies behind

History / Physics / Relativity

The Men Who Weighed Mountains

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 In 1687, Sir Isaac Newton published the Philosophiæ Naturalis Principia Mathematica, his magnum opus describing the laws of motion and the secrets of the universe. One such secret is Newton’s law of universal gravitation, which states that the same gravitational force that pulls us down to the Earth holds the planets in their orbits around the sun. Indeed, every mass attracts every other mass through gravity. This means that not only are we pulled downwards towards the Earth, but we are pulled towards pieces of the Earth. We are all gravitationally attracted to mountains. In fact, this is an excellent test of Newton’s

Astrophysics / Physics / Relativity / etc.

Simulating Gamma Ray Bursts

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It was the mid 1960s. The United States and the Soviet Union had recently signed the Partial Nuclear Test Ban Treaty, which forbid the detonation of nuclear weapons except underground. Since neither nation trusted the other, each was carefully monitoring the other for non-compliance. In particular, the United States feared that the soviets might be, I kid you not, testing bombs behind the moon. Vela The United States solved this problem with the Vela satellites. When a nuclear bomb goes off, it emits a short burst of gamma rays, which are rays of extremely high energy light. The Vela

Astrophysics / cosmology / Physics / etc.

The Universe Is an Inside-Out Star

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the CMB on our sky

No, not really. But as we’ll see, it’s a useful analogy. Today we’ll learn about sound waves in the sun and how, if we imagine that the universe is the sun but inside-out, these are the same as the sound waves that filled the early universe. DISCLAIMER: This is a pedagogical exercise only! I am not claiming the universe is ACTUALLY an inside-out star or that scientists think of it as one. Sound Waves in the Sun I’m sure you won’t be surprised when I say that the sun is a complicated beast. A nuclear furnace burning at tens

Astrophysics / Physics / Relativity / etc.

What Space Projects Excite Me: Multi-Messenger Astronomy

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The remnants of a supernova found in 1987

A few weeks ago, awesome blogger and space advocate Zain Husain asked me to contribute to a roundup post he wrote. He contacted a bunch of people (most of them much more prestigious than me) and asked them one question: What NASA or space project are you most excited about and why? You can (and should) read everybody’s response to Zain’s question on his blog, here. However, I wanted to expand on part of my answer and tell you why I’m excited about multi-messenger astronomy. Supernova Supernova It all starts with the title image above. That’s an image of

Condensed Matter / cosmology / Physics / etc.

BICEP2, Primordial Gravity Waves, and Cosmic Inflation

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“Like the microscopic strands of DNA that predetermine the identity of a macroscopic species and the unique properties of its members, the modern look and feel of the cosmos was writ in the fabric of its earliest moments, and carried relentlessly through time and space. We feel it when we look up. We feel it when we look down. We feel it when we look within.” ~Niel Degrasse Tyson There was some very big news today! If you haven’t already heard, the BICEP2 research group at Harvard has found evidence of ancient gravitational waves in the sky. A lot