Thought Problem

[Swindle1984]

I hope this is the right forum for this.

I've got a thought problem. I'm wondering if any of you guys, being a little geekier than I am about this sort of thing, can figure it out.

You are trapped inside a spaceship that is traveling at one gee. There are no doors or windows, and you have no way of contacting anyone outside (no radios, phones, etc.). You're being watched covertly and are not allowed to leave the spaceship until you can prove you're in space and not on earth. How do you prove that you're in space and not on earth?

So far, I suggested using a compass (which, unless I made some horribly stupid mistake, should either detect that there is no magnetic north or the spaceship's hull should provide uniform interference, resulting in about the same thing.) to get a decent idea, if not proof. I also suggested using a scintillator to pick up cosmic rays, which should be more abundant in space than on earth.

Some other idiot said watch which way the toilet flushes because of the coriolis effect.

Someone else suggested using a laser and firing it at a specific point at the top of the ship (or building, if you're really on earth and not in space) from the bottom. If you're in a ship accelerating, supposedly the laser will either take slightly longer to hit the target or will hit slightly off target. I don't get how you're supposed to measure the difference in the time it takes the laser to hit or why it would hit slightly off-target if the ship is accelerating in a straight line.

The only other thing anyone came up with is that the gravity felt at the top of the ship should be slightly less than at the bottom of the ship (but wouldn't that be true in a really tall building on earth too?). Nobody could think of a way to measure that, though I suppose using a measuring board and high speed camera (used to determine the velocity of an object) could help you detect a difference in the acceleration of an object dropped from the top of the ship and an object dropped at the bottom.

I dunno. IS there a way to prove that you're in a spaceship and not on earth?

[Surlethe]

If your spaceship is small enough (practically, building-sized fits the bill), there is no way to use gravitational acceleration alone to distinguish between being trapped in a spaceship-like house on Earth and being trapped in a house-like spaceship in outer space travelling at 1G. That is the whole point of the local equivalence between acceleration and gravitation.

If you had extremely sensitive equipment, however, you could measure tidal forces. Their presence or absence would confirm whether you were in a gravitational field or simply in a linear accelerator. You might also be able to measure the field difference between the top of the spaceship and the bottom, as suggested; it's there, if you're on Earth. It is, however, extremely small, just like the tidal forces; to measure either would require, as I said, very sensitive, precise equipment.

The easiest idea is probably the compass. You could also maybe use temperature to check, too.

[Ariphaos]

The first method that came to my mind was to build a pendulum to check for rotation. Amusingly, you can place a person on Earth somewhere where the compass or pendulum will not work, but never both.

Naturally, you can also very slightly rotate the cabin to deal with this, but there are more sensitive means that would pick out the improper rotation more clearly.

[GrandMasterTerwynn]

A loaded .44 Magnum ought to demonstrate whether or not you're in a spaceship. Though they could prevent you using this method in the same way they could stop you from spotting any higher cosmic radiation flux than what you might see atop a particularly tall mountain on Earth (which is to encase your habitat in the ship's water tank, or in enough paraffin and other non-metallic materials.) And there is the slight problem that this is a destructive test and you ought to have some epoxy and a fairly rigid patch on-hand if it turns out that you're aboard a spaceship.

[Ender]

A dosimeter or gamma or neutron radiac to tell the difference in background radiation.

[Kuroneko]

I was typing an expose on tidal forces, but then I saw that Surlethe already mentioned that. This kind of question is very open-ended in that we don't know the expected specs of the spaceship. For most realistic shapeships, you could pick up on the time-dependent variations of acceleration even easier than tidal forces. That aside, I kind of like Xeriar's Foucault's pendulum idea.

[Mad]

Someone else suggested using a laser and firing it at a specific point at the top of the ship (or building, if you're really on earth and not in space) from the bottom. If you're in a ship accelerating, supposedly the laser will either take slightly longer to hit the target or will hit slightly off target. I don't get how you're supposed to measure the difference in the time it takes the laser to hit or why it would hit slightly off-target if the ship is accelerating in a straight line.

That won't work. You'll always measure the same time regardless of your velocity. Light travels at c in all reference frames.

The only other thing anyone came up with is that the gravity felt at the top of the ship should be slightly less than at the bottom of the ship (but wouldn't that be true in a really tall building on earth too?). Nobody could think of a way to measure that, though I suppose using a measuring board and high speed camera (used to determine the velocity of an object) could help you detect a difference in the acceleration of an object dropped from the top of the ship and an object dropped at the bottom.

It'd be the opposite. In the spaceship, "gravity" will be uniform because the entire ship is accelerating at the same rate. In a building on Earth, the higher you are the less gravity you'll feel. The ship probably isn't tall enough for any significant measurement to be made, though.

Unfortunately, I don't have any ideas.

[Ayrix]

I was thinking about this and I don't know if this is a stupid observation or not: If you were going fast enough/had enough acceleration to be going 1g in a spaceship, wouldn't you be able to hear the engines or at least feel a good vibration throughout the deck?

[Kuroneko]

I was thinking about this and I don't know if this is a stupid observation or not: If you were going fast enough/had enough acceleration to be going 1g in a spaceship, wouldn't you be able to hear the engines or at least feel a good vibration throughout the deck?

Yes, that's what I was referring to above--realistic engines won't give you very smooth acceleration, and this should be much more easily detectable than tidal forces, even if it is smooth enough not to be felt with one's body. But then, we don't know what kind of engines to expect in this scenario, be they realistic or sci-fi technomagic.

[Lord of the Abyss]

I was thinking about this and I don't know if this is a stupid observation or not: If you were going fast enough/had enough acceleration to be going 1g in a spaceship, wouldn't you be able to hear the engines or at least feel a good vibration throughout the deck?

Yes, that's what I was referring to above--realistic engines won't give you very smooth acceleration, and this should be much more easily detectable than tidal forces, even if it is smooth enough not to be felt with one's body. But then, we don't know what kind of engines to expect in this scenario, be they realistic or sci-fi technomagic.

For that matter, if you are on Earth, the room might be mounted atop a machine designed to simulate the noise and vibration of an engine, anyway.