Scientific Questions

[Ed Kolis]

Isn't it funny how you can use solar sails to fly INTO the sun in SE4?

[AeoN2]

Originally posted by [K126]Mephisto:
IIRC photons have a very small mass and a very high momentum. With a larger sail (not THAT big, several hundred meters) you can gain very high speed over time because of the constant pressure applied by the light. However, it would be very hard to navigate with such a sail as you can only sail with the photons (i.e. away from the nearby sun) and have no force (like friction) to "cruise" lake a real ship can in water.

If I remember my physics correctly light both has mass, and acts as it has no mass at the same time. For instance no mass can travel at the speed of light (according to E=MC2), but it still has mass in other calculations... i am tired and know i am rambling now though

I know I've learnt about Mesons, but I can't for the life of me remember anything about them... My favourite subatomics have always been Gravitons (though I still don't think they have proven they exist, am I wrong?)

The latest I think heard about solar sails is that there is a new deep space probe that NASA are developing that will use a solar sail, I think they have successfully tested the technology... but it could be sleep-deprivation combined with too many Star Trek episodes

DISCLAIMER: Star Trek used as an example because it was mentioned earlier, truth be told I prefer B5

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AeoN2
--
Maugham's Thought:
Only a mediocre person is always at his best.

[Batman]

Photons *may* have an infinitesimally small mass, but it could also be zero (it's a topic of current physics research). The problem is that photons travel at the speed of light (by definition) and that as something approaches the speed of light its mass increases by a factor of

gamma = 1/(sqrt(1-v^2/c^2))
(where c is the speed of light and v is the object's speed)

which means that an object with mass should never be able to reach the speed of light, because it would have infinite mass and require infinite energy to accelerate further.

They have a momentum that is disproportionately high for their mass, but it isn't extremely high. If the photon momentum was too high, sunlight would knock you over

As far as the required size of the sail, you have to bear in mind that the further that you get from the star (or other source of light) the less dense the photons are.

If we take the output of photons to be constant, then the same amount of photons is spread over a spherical shell at a distance R from the sun. The area of this shell is A=4/3*Pi*R^3. A sail of area B captures B/A of the total photons emitted by the star. At double that distance from the star, the area of the shell is A2 = 4/3 * Pi * (2R)^3 = 8*4/3*Pi*R^3 = 8*A. So the same sized sail now captures only B/(8*A) of the total photons (because they are less dense). At double the distance, the sail is 1/8 as effective, and so on. So it should be big if it is to maintain effectiveness for the whole voyage.

[AeoN2]

Originally posted by Batman:
[QB]Photons *may* have an infinitesimally small mass, but it could also be zero (it's a topic of current physics research).QB]

I seem to remember a theory that may make it possible for information (not matter) to travel faster than light. It had something to do with to particles that split in opposite directions both travelling at the speed of light, but when the first got to its destination, it would always behave in the opposite way from its twin, so it could somehow be used to transmit information at the speed of 2C (and I really need that speedboost for my next computer )

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AeoN2
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Black holes are where God is divided by zero.

[Batman]

[quote]Originally posted by AeoN2:

Originally posted by Batman:
I seem to remember a theory that may make it possible for information (not matter) to travel faster than light.

You're talking about the EPR paradox (stands for Einstein-Podolsky(sp?)-Rosen).

Sometimes when a pair of particles are created, they have properties that depend upon one another. For example, spin is conserved, so if a particle with zero spin decomposes and sends two smaller particles off in opposite directions, the total spin of the situation still has to be zero. Therefore, one particle has spin "up" and the other has spin "down". From a quantum mechanical perspective, each of the two particles (let's call them left and right) has an equal chance of being the up particle. Now if I know a particle decomposed in this manner say, a light year away, and the left particle comes towards me and the right particle moves away, then they are both in a 'superposition' of the spin up and spin down states. It isn't until I measure or observe 'left' that it collapses into one of the two states (up or down).

Now, the paradox comes from the fact that the instant I observe left, right must also become fixed into the opposite state that I observe. So, supposedly, it must have "heard" what state left was in. Since this happens instantaenously, the information is transmitted from one particle to the other an infinite velocity.

Its worth noting that this scenario was put forward by Einstein, Podolsky and Rosen as a reason that quantum mechanics is nonsense.

This might not be 100% accurate, I'd have to get home and check some of my textbooks. Even if it is accurate, it probably isn't very well explained. Go to google +epr +paradox -"Star Trek Voyager"

[TerranC]

Originally posted by Batman:
Its worth noting that this scenario was put forward by Einstein, Podolsky and Rosen as a reason that quantum mechanics is nonsense.

[Mephisto]

I stand corrected.