Posts Tagged special relativity


Posted by on Tuesday, 19 November, 2013


funny cartoon about time travel


Time is mysterious.

So are cats but – hey! – this isn’t about cats. It’s about time. In this episode of “Five Minute Physics”, Henry Reich explains a bit about time travel. Pay attention to his second point.  Walking is traveling in time.

I bring this up because I intend to use that as a basis for Mister ScienceAintSoBad’s Time Machine.  After the video, keep reading, okay?

I’m back.

Now that you’ve seen the video, here’s my question: Does Einstein’s stuff about relativity mean that star travel isn’t practical because of the speed of light thing?

Not really.

Relativity describes the way things seem from various points of view. It describes what you see when you watch me fly off in my spaceship.

In this “observer” role, you watch me fly off in my ship and you notice that my speed starts to “adjust”  as I close in on the speed of light. You see me getting closer and closer to the speed of light but – damn! – those photons keep on passing me by. I can’t quite seem to quite reach their speed of about 186,000 mph. I’m the poster space ship for how nothing can go faster than the speed of light.

Bummer! It’s a hopeless case.

If we can’t go faster – a lot faster – we’ll never get to more than the few nearby stars. Maybe we could use cryonic suspension or wormholes or teleportation or some other form of cheating but, you know what? That doesn’t impress me because, as a form of travel, that stuff’s more fiction than fact.

So we’re left with the fact  that the speed of light, like you always heard, is the barrier. We’re s-c-r-e-w-e-d.

Here’s the thing though.

Say you, standing on the earth,  could see the clock in my spaceship. You would wonder what’s wrong with it. As the ship goes faster, the clock goes slower. As I get close to the speed of light, the clock moves so slow you wonder if it is moving at all. This is as Einstein said.

I visit my destination and return to Earth.

I land. You’re waiting for me.

Your hair is gray, you use a cane, and you have something going on with your prostate.

Me? I look pretty much the way I did when I left.

You say you’re so glad to see me after 37 years. I say it was only a 3 day mission and I don’t know what you’re talking about.

Why aren’t I older?

My clock.

As I pointed out, the faster I go, the slower goes my clock. The clock, in these examples, isn’t “just a clock”. It’s a way of showing that time, itself, goes slow.

Crazy. But that’s relativity.

That’s why I only age by three days.


You were the “observer”. To you, 37 years – real years- went by. To me, only three days went by. I traveled 37 light years in three days which is a lot faster than the speed of light. For me.  Not for you.

That’s how it works. Speed is my time machine. Go fast enough, and I can go anywhere.

Seriously! I can go anywhere I want, as far as I want, out into space. All I have to do is stick close to the speed of light.  The price I  pay is back home. The faster I go, the greater the difference in our clocks – mine vs those back on Earth. Soon I’m out beyond the lifespan of anyone I know. Eventually? Generations will have passed.  Maybe all of humanity is gone.

Don’t blame this on me. I’m no Einstein.

A final note.

I wrote this to address the misconception that you “can’t go faster than the speed of light”. To explain that, while this is true for the observer, it isn’t true for the traveler. At least, not after the traveler returns to his.her point of departure – an important point to consider.

I wouldn’t want you to try this without checking with me. We don’t have any space ships that could go anywhere near that fast.  And we don’t have a way to handle the radiation which would be absorbed on such a trip. And – even if that weren’t a problem – we would risk a collision with the most minute of particles which, at that speed, would pack enough energy to blow up the ship.

The practical problems of near light speed take it off the menu for us. But don’t blame Einstein.

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The cartoon is mine.