Is space dark?

[CaptainChewbacca]

I'm an educated fellow, but I can't figure it out. We've all seen the movies where the spaceship is light-years from the nearest system and is brightly lit. Is this the case, or would being in space be as bright as being outside when there's no moon and a clear sky?

[Lord Zentei]

I'm an educated fellow, but I can't figure it out. We've all seen the movies where the spaceship is light-years from the nearest system and is brightly lit. Is this the case, or would being in space be as bright as being outside when there's no moon and a clear sky?

If it is situated light years from the nearest system, a spaceship should not be lit. This is an example of "creative licence" in sci-fi movies (it would be pretty boring to see nothing but a black screen, after all).

[GrandMasterTerwynn]

I'm an educated fellow, but I can't figure it out. We've all seen the movies where the spaceship is light-years from the nearest system and is brightly lit. Is this the case, or would being in space be as bright as being outside when there's no moon and a clear sky?

If a ship is in deep space, lightyears away from anything, it wouldn't be lit very well at all. Even on a moonless, clear night on Earth, you'll still have airglow from some nearby town or city (or from the dust in the atmosphere spreading out the light from all the stars) mucking things up.

In deep space, you wouldn't have that sort of glow. So the only things that would light up a ship in deep space would be whatever running lights, active engine exhausts, stupidly placed windows, etc, the ship happened to have.

[dworkin]

Starships are well lit for the same reason that no-one inside will wear a pressure suit during battle.

[CJvR]

It depends on where you are in relation to the nearest stars. In the inner parts of a solar system you will always have light unless you are in a planetary shadow. On the outer edges of a system or in interstellar space you will have the equivalent of a starry but moonless night.

[Admiral Valdemar]

It depends on where you are in relation to the nearest stars. In the inner parts of a solar system you will always have light unless you are in a planetary shadow. On the outer edges of a system or in interstellar space you will have the equivalent of a starry but moonless night.

In interstellar space, the ship should be all but invisible. The many lights in the sky from distant stars don't throw that much of anything in the way of light on objects in space. Only in a solar system, as you and other state, should a ship be visible on the solar side.

[The Third Man]

This question is reminiscent of the interesting matter of Olbers Paradox, which basically asks: Why, if there are an infinite number of stars, isn't the night sky uniformly bright? In other words, and in the context of the OP: Even though the vastly distant stars contribute only an infinitesimal amount of light to the illumination of our spaceship, there is however an infinite number of stars, so all the infinitesimally small contributions should add up to an exceedingly bright light.

There are, apparently, various answers to the paradox, the obvious one being that with the universe being only 15 billion years old, we can only see that light which has travelled for less than this time - ie light from those stars within a 15 billion light-year radius. There's also the effect of red-shift to take into account - light from the more rapidly receeding stars will be red-shifted clean out of the visible spectrum.

More on Olbers Paradox here here, here (Google Answers) and here (PDF with maths)

[SyntaxVorlon]

Space is clear. It's just that at a point the universe is a red so dull it falls into microwave wavelengths, because of the doppler effect the edge of the universe appears to be moving away from us superluminally, this stretchs wavelengths out. The fact is that it has so few photons to see that it can't provide illumination.

[Kuroneko]

I think this came up before, but... there is a finite limit to the speed of interaction, c, and a maximal force, F = c^4/(4G), making the highest possible power Fc = c^5/(4G) ~ 1e52W. If any portion of the universe attempted to generate more power, a horizon would form that would shield the rest of the universe from it. It is then completely unsuprising that we do not observe arbitrarily high amount of radiation--we can't; it is a physically impossible situation.

The force limit is enforced by Einstein's field equation, but it can be understood more intuitively by observing what happens in special relativity. Acceleration is the rotation of the velocity four-vector, and under the Minkowski metric, this produces a hyperbola in the (t,x) plane (let's supress the two extra spatial dimensions). Like all hyperbolas, it has an asymptote, and if the object is far enough way from the origin and the acceleration is great enough, this asymptote will fall below the t = x line that represent a luminal signal: in other words, no signal from the origin will be able to reach the object while it is undergoing this extreme acceleration, even though the object's speed will always be subluminal (the reverse is not true; the object can freely send signals to the origin). This is called acceleration (or Rindler) horizon, and is it is an obvious problem for spatially extended (non-point-like) objects--if the acceleration is great enough, the back of the object becomes causally disconnected from the from the front, and the horizon breaks the object no matter how strong the material is. Since the size of the object is has a lower limit for a given mass (the Schwarzschild diameter), the maximal force the object can experience can be computed in this way.