So I did an interview for the “Tilting at the Universe” podcast. In it, I describe: the history of dark energy and the expanding universe, how the mystery of dark energy may be solved once we reconcile quantum mechanics and general relativity, how the astrophysics of black holes and neutron stars may help us understand quantum gravity, and how my field of numerical relativity fits in to all of this. I think I did a pretty good job of explaining what excites me about the field. So check it out. The interview is here. In the interview, I mention

# General Relativity

##### Physics / Relativity / Science And Math

# The Direction of LIGO’s Gravitational Waves

On September 14th, 2015, the LIGO gravitational wave observatory network detected the gravitational waves from the merger of two black holes. In moments, the LIGO team estimated (very broadly) where the black holes were located in the sky; these regions are highlighted in figure 1. Today I tell you how they figured this out. And why it’s important. Electromagnetic Counterparts First, let’s talk about why the direction of the waves is important. When LIGO detects gravitational waves, those waves can tell us an awful lot about their source. Just from the waveform, LIGO learned that the waves from December

##### Astrophysics / Physics / Relativity / etc.

# The Black Holes that Created LIGO’s Gravitational Waves

A little over a week ago, the LIGO collaboration detected gravitational waves emitted during the in-spiral and merger of two black holes. And the world’s scientists, myself included, collectively went bananas. Last week, I attempted to summarize the event and capture some of the science, and poetry, that has us so excited. In short, gravitational waves provide us a totally new way to look at the universe. LIGO’s one detection has already provided us with a wealth of information about gravity and astrophysics. Today, I summarize some of what we’ve learned. Black Holes As We Knew Them In the

##### Astrophysics / Physics / Relativity / etc.

# The Poetry of LIGO’s Gravitational Waves

Yesterday the LIGO scientific collaboration announced that they had detected the gravitational waves from the in-spiral and merger of two black holes, shown in figure 1. It would not be an overstatement to say that this result has changed science forever. As a gravitational physicist, it is hard for me to put into words how scientifically important and emotionally powerful this moment is for me and for everyone in my field. But I’m going to try. This is my attempt to capture some of the science—and the poetry—of LIGO’s gravitational wave announcement. The Source About 1.3 billion years ago

##### Astrophysics / Physics / Relativity / etc.

# The Geodetic Effect: Measuring the Curvature of Spacetime

A couple of weeks ago, I described the so-called “classical tests of general relativity,” which were tests of early predictions of the theory. This week, I want to tell you about a much more modern, difficult, and convincing test: A direct measurement of the curvature of spacetime. It’s called the geodetic effect. This is the eighth post in my howgrworks series. Let’s get to it. We know from general relativity that gravity is a distortion of how we measure distance and duration. And that we can interpret this distortion as the curvature of a unified spacetime. When particles travel

##### Physics / Quantum Mechanics / Relativity / etc.

# The Holometer

You may have heard the buzz about the holometer, shown in figure 1, before. It’s a giant laser interferometer, much like those used to search for gravitational waves, designed to detect quantum fluctuations in the fabric of spacetime. At least, that’s the claim. The holometer just released a preprint of their first science paper. And of course, a Fermilab press release appears in Symmetry Magazine. The article is good, and I recommend you read it. And the holometer experiment is good, interesting science. But I have to say, I’m extremely annoyed by how much the holometer team is overselling their

##### Physics / Relativity / Science And Math

# Classical Tests of General Relativity

Last Wednesday, November 25, was the 100 year anniversary of general relativity. It was the precise day that Einstein presented his field equations, shown in figure 1, to the world. In celebration of this anniversary, today I present to you some of the early triumphs of general relativity, classical predictions of the theory that have been precisely tested and where theory has exquisitely matched experiment. This is the sixth instalment of my howgrworks series. Let’s get started. The Perihelion of Mercury Before Einstein, we believed that the motion of planets in the solar system were governed by Kepler’s laws

##### Geometry / Physics / Relativity / etc.

# In-Falling Geodesics in Our Local Spacetime

My previous post was a description of the shape of spacetime around the Earth. I framed the discussion by asking what happens when I drop a ball from rest above the surface of the Earth. Spacetime is curved. And the ball takes the straightest possible path through spacetime. So what does that look like? Last time I generated a representation of the spacetime to illustrate. However, I generated some confusion by claiming that it “should be obvious” that the straightest possible path is curved towards or away from the Earth. When a textbook author says “the proof is trivial”

##### Geometry / Physics / Relativity / etc.

# Our Local Spacetime

General relativity tells us that mass (and energy) bend spacetime. And when people visualize the effect of a planet on spacetime, they usually imagine something like in figure 1, where the planet creates a “dip” in spacetime much like a “gravitational well.” But today I’m going to show you what spacetime actually looks like near a planet… and it doesn’t look anything like the common picture. This is the fifth part in my many-part series on general relativity. Here are the first four parts: Galileo almost discovered general relativity General relativity is the dynamics of distance General relativity is

##### Physics / Relativity / Science And Math

# Distance Ripples: How Gravitational Waves Work

Gravitational waves are “ripples in space time” that propagate through it like waves on water. That’s the common story and, for the most part, it’s right. But what does that mean? This is part four in my many-part series on general relativity. The first three parts introduce general relativity from the ground up. You can find them here: Galileo almost discovered general relativity General relativity is the dynamics of distance General relativity is the curvature of spacetime Okay. Without further ado, gravitational waves! Spooky Action at a Distance First, I want to help you get an intuition for why