Ask Ethan: Is Spacetime Really A Fabric?

[Judi Lynn]

Aug 11, 2018, 10:00am

Starts With A Bang
Ethan Siegel Contributor
Starts With A Bang



Gravity might have been the first fundamental force ever discovered, but in many ways, it remains the least-well understood. We know that it's always attractive, and that any two masses in the Universe, no matter where they are, will experience its force. When Einstein concocted his general theory of relativity, one of the great advances was to recognize that space and time were combined into a single entity: spacetime. Another was that the presence of matter and energy curved the very fabric of this spacetime, and that curved spacetime, in turn, dictated how matter moved. But is this picture right? Mariusz Wroblewski is skeptical, asking:

I'd like somebody to finally acknowledge and admit that showing balls on a bed sheet doesn't cut it as a picture of reality.

I freely acknowledge and admit it. As ubiquitous as pictures of bent sheets or coordinate systems are, they aren't exactly reflective of the reality we inhabit.

If you've ever seen a picture of a bent, two-dimensional grid with masses on it representing space, you'll know this type of illustration is extremely common. It appears to depict the fabric of space as being curved by the presence of mass, and therefore, any other particle traveling along this fabric will have its path bent towards this gravitational source. The larger the mass and the closer you get to it, the larger the curvature, and therefore, the larger the bending.

More:
https://www.forbes.com/sites/startswithabang/2018/08/11/ask-ethan-is-spacetime-really-a-fabric/#4645a4a297fc

[JayhawkSD]

1. Just watched Deja Vu with Denzel Washington

Not really on topic, I guess, but this is a wonderful movie which has an entertaining and marvelously adept handling of time warp. It twists and turns and is both suspenseful and delightful. Denzel's character goes batshit when he realizes a time warp is in play and, among other things, smashes a computer and asks if it is broken or not. "It did not," he rants, "transition itself into a different state of entropy, so is it broken or is it not broken?"

It's about the third time I've watched this movie and, even knowing what's coming, I'm delighted by it and always just slightly surprised.

[Duppers]

2. "When Einstein *concocted*!

Last edited Sun Aug 12, 2018, 08:06 AM - Edit history (2)

"Concocted"?! What a word choice. Einstein spent 15yrs developing his Theory.