Ask Dr. Science

Query:

> Speaker
	Assume for a minute that we have the ability to create long range spacefaring vessels. And assume for a moment that we have the technology to not only collect photons, but control them. Now, due to the fact that photons have null gravitational mass in relation to the universe, if we were to create a "bubble" (does dr. evil finger quotes) of photons around this, what I would like to call, "starship" then obviously the bubble...and the starship would have null gravity with relation to the universe. Since all inertial forces are out of the equation, then technically we could now speed this bubble up to infinite! My question finally...in this scenario, could we use engines on the SHIP itself to propel it this fast or would we have to propel the bubble (the latter makes more sense to me), and if so...HOW could we propel a bubble without having to compensate for the gravitational mass of the external ...umm...would it be a "pusher?" I don't know! I'm not a quantum physicist!!! PLEASE HELP ME! I can not stop thinking about it!

The Experts Respond:

>Mega Man
	Speaker, you've made our Christmas. Hey guys, who wants to play a round of "Let's Assume That?"

> Albert Einstein

Photons don't exactly have "null gravitational mass (ngm)". Their paths can be altered in the presence of a gravitational field, for example, those surrounding a planet or a star. In fact, that phenomenon is used to detect large extrasolar planets. I agree that, for most bodies and over reasonable distances, yes, photons appear to have ngm, but over interstellar distances, that's not a valid assumption. Next!

> Tron Bonne

But, let's assume that photons do have ngm. If you were to create a "bubble" of photons around a starship, that wouldn't automatically give it ngm. Think about it this way. The earth is basically enveloped in a vacuum, but even so, it still has a mass, and experiences the gravitational field surrounding the sun. Hand off!

> Professor Utonium

Now, let's assume that the spaceship/bubble duo did have ngm. If the spaceship were to fire its engines, there would be no mass for the thrust to act upon. Therefore, the spaceship would go nowhere. This would be true for any force acting on the bubbleship, regardless of whether or not the force was the engine thrust, or an external "pusher". Hot potato!

> Bunsen Honeydew

For the sake of discussion, let's assume that some sort of external "pusher" could be affixed to and could propel the bubbleship. You're right in noting that the pusher's mass would be a problem, in that the bubbleship no longer has ngm, and therefore couldn't approach infinite speed. You could just wrap the pusher in a bubble of photons to fix this problem, but in compliance with our earlier assumptions, the pusher's thrust would be ineffectual at that point. Heads up!

> Lucca Ashtear

Finally, let's assume that you could propel the ship with no external pusher. I can see two immediate problems arising from the fact that the bubbleship has ngm. First, how would you stop it? With no inertia or friction, it should just keep on truckin' through the cosmos. Second, no mass means no momentum. If the bubbleship collides with even the most ifinitesimal particle with the most ifinitesimal speed, it'll be deflected, and be sent flying off course, if not outright destroyed.

> Roll

ROCK!

> Mega Man

Yes?

> Roll

No, no, I meant... ah, never mind.

> Lucca Ashtear

And that concludes another episode of "Let's Assume That"! Thanks for playing, Speaker!

> Albert Einstein
	Photons don't exactly have "null gravitational mass (ngm)". Their paths can be altered in the presence of a gravitational field, for example, those surrounding a planet or a star. In fact, that phenomenon is used to detect large extrasolar planets. I agree that, for most bodies and over reasonable distances, yes, photons appear to have ngm, but over interstellar distances, that's not a valid assumption. Next!

> Tron Bonne
	But, let's assume that photons do have ngm. If you were to create a "bubble" of photons around a starship, that wouldn't automatically give it ngm. Think about it this way. The earth is basically enveloped in a vacuum, but even so, it still has a mass, and experiences the gravitational field surrounding the sun. Hand off!

> Professor Utonium
	Now, let's assume that the spaceship/bubble duo did have ngm. If the spaceship were to fire its engines, there would be no mass for the thrust to act upon. Therefore, the spaceship would go nowhere. This would be true for any force acting on the bubbleship, regardless of whether or not the force was the engine thrust, or an external "pusher". Hot potato!

> Bunsen Honeydew
	For the sake of discussion, let's assume that some sort of external "pusher" could be affixed to and could propel the bubbleship. You're right in noting that the pusher's mass would be a problem, in that the bubbleship no longer has ngm, and therefore couldn't approach infinite speed. You could just wrap the pusher in a bubble of photons to fix this problem, but in compliance with our earlier assumptions, the pusher's thrust would be ineffectual at that point. Heads up!

> Lucca Ashtear
	Finally, let's assume that you could propel the ship with no external pusher. I can see two immediate problems arising from the fact that the bubbleship has ngm. First, how would you stop it? With no inertia or friction, it should just keep on truckin' through the cosmos. Second, no mass means no momentum. If the bubbleship collides with even the most ifinitesimal particle with the most ifinitesimal speed, it'll be deflected, and be sent flying off course, if not outright destroyed.

> Lucca Ashtear
	And that concludes another episode of "Let's Assume That"! Thanks for playing, Speaker!