FTL Travel and the Rear of the Moon

Adam Hrankowski

2 Thought Experiments To Mess With Your Head

For our first demonstration you will need your cat, a laser pointer and the Moon.

Place your cat on the Moon. (Take necessary precautions to ensure the well-being of your cat.) Fire up the laser pointer and point it towards the Moon. (You will need a strong battery or a stronger imagination. Both, if you have them.)

Your cat will recognize her nemesis, the Glowing Red Spot of Doom (GRSD) and launch an attack.

Your cat is fast. But can she outmanoeuvre the GRSD?

It’s doubtful.

The distance between the Earth and the Moon magnifies the slightest motion in the laser pointer. You can easily nudge that pointer so the GRSD moves faster than the speed of light.

To drive this point home, place another moon (if you have one) in orbit around the Earth. While the (capital M) Moon is in the east, and the other (lower-case m) moon is in the west, flip the pointer back and forth between them.

The two satellites (Moon and moon) are separated by more than 800,000 kilometres. Yet, the GRSD traverses that distance in a fraction of a second. (Try it!) The speed of light is (only) 300,000 kilometres per second.

Even a thought-experiment cat can’t travel faster than light. How does the Glowing Red Spot of Doom achieve faster than light travel?

While you are pondering this question, return your (frustrated) cat to Earth. Place her in a sunny spot just before a total solar eclipse. You want her to cast a crisp shadow on the ground.

Place a small object in that shadow. A mouse will do.

Now that your cat is casting a shadow on the mouse, wait for the Moon to obscure the sun.

During the total eclipse, which shadow is on the mouse?

Is it still the cat’s shadow? The cat is in total darkness. How is it casting a shadow?

It must be the Moon’s shadow. But how can the mouse be in the Moon’s shadow? The Moon is behind the cat. Do we say that during an eclipse we are in the shadow of the far side of the Moon?

During the dark of night, would you say that Mount Everest (or some other object on the other side of the planet) is casting a shadow on you?

Both of these scenarios describe what might be called a thought illusion. It’s easy to think of a shadow as a thing, so that’s what we do. But a shadow isn’t a thing. That’s a convenient fiction, until we push it beyond its capability. Then we have to deal with a lunar shadow traveling through a cat and hitting a mouse. Or a darkened cat casting a shadow.

Likewise, the Glowing Red Spot of Doom isn’t a thing. Nothing is moving faster than light.

To drive that idea home, imagine the Spot somehow carrying information from your cat to the other moon. Suppose your cat wants to tag the Spot with a message for a mouse on the other moon. The Spot isn’t a thing, so your cat can’t do it.

However, if your cat ever claims to have caught the Spot, give her lots of praise. And a (catnip) mouse.

[Originally published by the Author on Medium]

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I thought I was a renaissance man. Turns out I have ADHD.


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