Spacetime

First, be sure to check out Mars this week. It has just gotten extremely bright, obvious and pale orange, while retrograding to hover now just above the blue star Spica in Virgo. Their combined color contrast is gorgeous. It merits a peek toward the east anytime after 10 p.m. or so.

Now to the weird stuff: Last week’s talk at WAMC’s Linda Auditorium in Albany explored space and time a little bit, and everyone seemed so fascinated that it’s probably worth a little attention here.

We’ve known for a century – thanks to Einstein – that time is not real. Rather, events elapse at different rates depending on the local gravity or the speed of the observer.

Space, too, has no absolute reality. It is not empty (since all space is permeated by microwaves, along with, most likely, a super-powerful, all-pervading vacuum energy).

Moreover, the distance between objects can wildly mutate. We may imagine that there’s a non-variable gap between us and another galaxy, but that separation physically alters depending on various factors. The bottom line (never mentioned on TV science shows) is that the cosmos is fundamentally sizeless.

With space and time each demoted from their previous incorrect status as a kind of framework in which everything dwells, we’re left with a far more astonishing universe. And, as we’ll discuss in a few weeks after the upcoming eclipse, other recent discoveries show that space or distance may not constitute the reliable boundary between events or objects that we used to assume.

What about spacetime? Einstein invented the term to describe mathematically how objects move. He replaced gravity with a kind of geometry, showing that bodies distort their surroundings and thus determine how they and anything else will travel.

A common mistake is imagining spacetime as an actual thing, like pizza – and picturing the universe permeated by this mysterious invisible substance. In truth, spacetime is not an actual entity, but a way of mathematically understanding motion and events. By retaining the traditional view of space and time as separate and independent, and considering both as real and immutable, paradoxes arise at high speeds and in strong gravitational fields. To avoid such contradictions, and also to view all points of view and frames of reference democratically, as equally valid, with no privileged positions in the universe, then time has to warp depending on circumstances; and space, too, must shrink or bend.

This notion was so radical early in the 20th century that nobody could really believe it. Was it possible that a mile of distance to you could be experienced as an inch to me? Could light take a curved path to our eyes through empty space? Could a million years pass on Earth while a mere second elapsed for someone else in the cosmos?

We now know, without any doubt, that the answer to all these is “Yes.” We actually witness the bending of space. We routinely measure the slowing of time. It’s fact, not theory.

To navigate through this strange new universe, Einstein came to our aid with the complex field equations of General Relativity: the Esperanto of the cosmos. But the equations are so tedious, they’re avoided even by NASA when sending spacecraft to other planets. At slow speeds or in relatively weak gravity, Newton’s Laws work just fine, thank you, and are far simpler to use.

In short, spacetime is a mathematical description of how things move, necessary only in conditions that none of us encounter: lethally intense gravity or speeds thousands of times faster than a bullet, or to know why Mercury’s orbit slowly and slightly shifts its orientation over time. But if you obey the speed limit and keep away from the Sun’s subtly space-distorting mass, the need for spacetime will never arise.

Want to know more? To read Bob Berman’s previous “Night Sky” columns, visit our Almanac Weekly website at HudsonValleyAlmanacWeekly.com.