General relativity warps space and time, and astronomers can use that fact to their advantage.
Spin Flip
As two black holes are close to merging, their spins do a gravitational dance that cause them to change direction.
The Strangest Theory We Know Is True
After 99 years, Einstein’s greatest scientific achievement is undefeated.
In the Red
If you toss a ball into the air, it will slow down as it rises. The Earth’s gravity pulls on the ball as it moves upward, causing it to slow down until it comes to a momentary stop at its highest point. Then it will begin to move downward, speeding up as it does. Suppose, then, that you were to shine a flashlight upward. What would happen? You might argue that gravity would pull on the photons, causing them to slow down, but we know that light has a constant speed, and can’t slow down. You might argue that since photons are massless gravity doesn’t affect them, but we know that the Earth’s mass, like any other mass, can cause light to change directions. So neither of these can be the answer. The real answer is pretty interesting, and it turns out to be one of the tests of Einstein’s theory of relativity.
Bend It Like Newton
Yesterday’s post on testing the assumption that photons are massless raised a few questions for readers. One of the most common was the idea that the gravitational lensing of light must mean that photons have mass. After all, if a star or galaxy can deflect light gravitationally, doesn’t that mean the light is gravitationally attracted to it? If that is the case, doesn’t that mean that light has mass?
Down the Rabbit Hole
Black holes are interesting objects, because we know they exist but we don’t know what they are. That isn’t quite true. We know that they are formed from the gravitational collapse of matter, either as supermassive black holes in the centers of galaxies, or as stellar mass black holes from the collapse of a star. We know that they power quasars and radio galaxies, that they can form accretion disks of matter around their equators, and that they can produce powerful jets of matter when they are active. But buried within our understanding of black holes is a fundamental contradiction that we have yet to resolve.
Make It So
In the popular science fiction franchise Star Trek, there are two ways in which a ship can move. Impulse engines, and warp drive. Impulse engines actually exist. Impulse is just a physics term for applying a force over a period of time, so impulse engine is just a fancy term for rockets. In the franchise they are usually assume to be some kind of plasma rocket, but they are still just rockets. In fact, any engine that applies a force over time is technically an impulse engine. So the next time you climb into your car you can “engage impulse engine”.
There And Back Again
When someone mentions time machines, you might think of fantastical machines such as Dr. Who’s TARDIS or the DeLorean in Back to the Future, but several physicists have made a serious study of time machines. Most of this work focuses on “what if” scenarios, which are really about testing the limits of a particular theoretical model, rather than actually engineering a device that can travel to the past.
Cosmic Pi
Today is March 14, which many celebrate as Pi Day since the month and day mark 3.14, which is approximately pi.It is also Albert Einstein’s birthday, so it seems fitting to ask whether π can exist in a universe as Einstein described it. Just for fun, I’m going to outline why the answer is no.
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