Geometry / Physics / Relativity / etc.

Our Local Spacetime

Gravity Probe B circling Earth

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

Astrophysics / Physics / Relativity

The Curvature of Spacetime

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

Condensed Matter / cosmology / Physics / etc.

BICEP2, Primordial Gravity Waves, and Cosmic Inflation

“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

cosmology / Geometry / Mathematics / etc.

For There We Are Captured—The Geometry of Spacetime

All about me there are angles— strange angles that have no counterparts on the earth. I am desperately afraid. ~Frank Belknap Long, The Hounds of Tindalos Whoever…proves his point and demonstrates the prime truth geometrically should be believed by all the world, for there we are captured. ~Albrecht Durer I was recently asked: What does it mean when we say spacetime is “curved” or “flat?” The answer lies in the interface between differential geometry and physics. This is the latest in many articles I’ve written on Einstein’s relativity, so you might want to check out my series on faster-than-light

Geometry / Mathematics / Physics / etc.

FTL Part 3: General Relativity Lets us Take Shortcuts

People assume that time is a strict progression of cause to effect, but actually, from a non-linear non-subjective viewpoint,it’s more like a big ball of wibbly-wobbly, timey-wimey… stuff. ~The Tenth Doctor (David Tennant) This is part three of a multipart series on faster-than-light travel. In the first part of the series, I explained why the speed of light is constant, no matter the observer. In part two, I explained why this invariance prevents us from going faster than light. This time, I’ll explain how we might use general relativity to get around this restriction. Fair warning: although general relativity