Tighten your seatbelts!

You’re just not going to believe what we’re going to do today! We’re going to venture into the Fourth Dimension, the dimension of space-time. This is going to be fun!

Getting there is a bit simpler than you might imagine.

First of all, we’re going to eliminate the clumsy and distracting hyphen; from now on it will be spacetime. See, it’s simpler already.

Second, we’re going to take notice that we operate in spacetime without even realizing it. Here is a spacetime coordinate:

“Meet me in the building at the northeast corner of Broadway and Main Street in Suite 901 at 7 PM.”

From this, we know that we have to go to the corner of Main and Broadway, which are dimensions on a grid of length and width. We also know that Suite 901 will be on the 9^th floor, a dimension of height. Finally, the 7 PM coordinate is the dimension of time. Guess what? You’ve entered the fourth dimension—spacetime.

Been here all along and just didn’t realize it, huh?

What is different when considering spacetime is that it defines events. So it is not a measure of abstract concepts, but of occurrences at specific places at specific points in time, or the assumption of such occurrences, even if they are imaginary.

It is complicated a bit when you stop to consider that time is not constant. As Albert Einstein proposed in his theory of Relativity, and has since been demonstrated in experiments, time can be dilated, or expanded, by speed, also called velocity.

I’m sure we’ve all seen the educational programs on TV that explain how an astronaut, traveling in space at a very high rate of speed, would experience much less time than would his twin brother who remained on the earth. Depending how close to the speed of light the astronaut was traveling, he might return to earth to find his twin an elderly man while he remained much younger.

Okay, that part I’m not even going to try to explain. First off, I’d have to understand it. And then, I’d have to learn to use PowerPoint. In broad terms, though, it makes events in spacetime subject to some complex formulas that are peculiarly significant in various realms of physics.

And while we’re on the subject, gravity can affect spacetime, too.

But right now, let’s have some fun with time dilation. Consider this:

1. The earth makes one revolution on its axis every 24 hours.
2. At the equator, a midpoint line furthest from the axis, the circumference of the earth is about 25,000 miles.
3. At the 45^th Parallel, a line halfway between the equator and the North Pole that runs through parts of the northern United States and southernmost Canada, the circumference of the earth is only about 12,500 miles.
4. Therefore, in a 24-hour rotation, people on the equator travel about twice as far (25,000 miles) as people at the 45^th Parallel (12,500 miles).
5. And so, people on the equator age more slowly than people of the north because they’re traveling faster at the equator. Just keep in mind that the difference is so infinitesimal it would not really be noticeable in human terms. You really have to be traveling much closer to the speed of light (186,000 miles per second) to make a significant difference.

But what’s really fun is this: because of the earth’s rotation, residents of Canada age faster than residents of the United States! Hah! Take that to your crummy government-controlled socialist healthcare clinics, Comrades, and wait in line to see if you can get that cured.

Actually, Canada’s healthcare system makes a lot more sense than ours. The problem is, they know it and are laughing at us behind our backs because we believe all the false accounts the right wingers put out. So let the Canadians age faster! That’ll teach them to snicker at The Greatest Country in the World!

And that’s how spacetime works.

Any questions?

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Let's get started

Word has it that the universe is expanding.

My question is, expanding into where, exactly?

I thought the universe, by definition, included EVERYTHING EVERYWHERE. So you can imagine my surprise to learn that there may be some places that everything everywhere does not include.

It may be just a matter of semantics. Apparently universe has different definitions, one or two of which are of fairly recent invention.

For instance, it has been proposed that the universe should only include those parts of intergalactic space with which we have at least the potential of interacting. For these purposes, potential is limited only by the speed of light and interacting includes any form of perception. By this definition, the universe would have a radius of about 46 billion light years. Beyond that distance, objects are moving away so fast that light from them would never reach us.

Now that's all well and good for some astrophysicist stuck in some lab or observatory, but I'm a traveling man, and I throw a pretty wide loop. If it's out there, whether I can see it or not, it's in my universe.

Then there is the definition which finds our universe to be just one of a potentially infinite number of universes which are unable to interact. This is the multiverse theory. Well, I say hah! to that, and see above.

One of the reasons that the multiverses cannot interact is due to their probable operation on entirely different and incompatible physical laws. Our laws of physics now envision a continuum of space and time; these two concepts are just different ways of describing the same thing. (That almost makes it sound like I understand that, doesn't it?) Notably, this would mean that space-time is contained within our universe; outside of our universe, space-time may not exist.

Neat. I can see the billboards just beyond the edge of our expanding universe:

Somewhere without time. Interesting thought. Seems like that's how I got started on this whole business, kneeling in church oh so many years ago, thinking about the meaning of eternity.

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