Thursday, December 6, 2012

NASA Aims for Faster than Light Space Travel

Perhaps you have heard that NASA has recently set its sights on building a spacecraft that can traverse space at a rate greater than 300,000 km/s - the speed of light.  The final product may well arrive a century from now, but at first glance, the very prospect of a spacecraft exceeding the speed of light seems to violate special relativity.  One of the first things we learn when studying relativistic physics is that 300,000 km/s is a cosmic speed limit.

Before investigating this apparent violation of physical law, let us examine what a faster than light speed spacecraft really means in the context of current space travel standards.
The Sun is roughly 8 light minutes away from the Earth.  This order of magnitude of distance indicates that if we were to travel near light speed within our solar system, we could fly by each of the eight planets in a matter of hours.  Why then does a transit from Earth to Mars take approximately six months?  Because at present, our spacecrafts travel merely tens of km/s at most.  They reach speeds nowhere near that of light.

However, using current methods of propulsion, it is theoretically possible (though extremely energy intensive and therefore prohibatively costly) to accelerate a spacecraft to near the speed of light.  It is based on the conservation of momentum principle: mass is shot out the back to propel the body forward.  It is highly impractical to reach such speeds, though not theoretically impossible.

If we would like to travel to the nearest star other than the Sun (Alpha Centauri, approximately 4.24 light years from Earth), it would take us slightly more than 4.24 light years travelling near the speed of light.  This being said, almost no time would elapse during this trip for us as the passage of time slows down more and more the faster we travel.  We could leave Earth after lunch, arrive at Alpha Centauri, orbit for a few hours, and then return home for supper.  However, on Earth, about 8.5 years will have elapsed; our children would be adolescents and 'last month's' unpaid credit card statement would have accrued some serious debt.

This huge discrepancy in passages of time is a direct consequence of special relativity.  Might it be possible to reduce this discrepancy of time?  Might it be possible, in theory, to reduce the 'Earth time' transit time from 4.24 years to something more reasonable?

In 1994, Miguel Alcubierre discovered an interesting way to legally defy the cosmic speed limit:

"… within the framework of general relativity and without the introduction of wormholes, it is possible to modify a spacetime in a way that allows a spaceship to travel with an arbitrarily large speed. By a purely local expansion of spacetime behind the spaceship and an opposite contraction in front of it, motion faster than the speed of light as seen by observers outside the disturbed region is possible. The resulting distortion is reminiscent of the ‘warp drive’ of science fiction."

What Alcubierre is saying is that the spacecraft itself is not traversing space at a rate greater than the speed of light, rather, space itself is expanding (behind) and contracting (in front) appropriately so as to propel the body forward.  The key then is to have a device on the spacecraft that expands and contracts the space around it accordingly.  This very phenomenon is what a NASA project led by physicist Harold White aims to do.  He and his team are attempting to create a "proof of concept" warp drive, using the theory behind what has come to be known as the Alcubierre Drive.

If this experiment is successful, it can be scaled up.  That being said, there is a difference between practically possible and practically viable.  The creation of an operational spacecraft with warp drive may become a question of input energy.  If the required amount of energy is unreasonable, then such a vehicle would fall under the category of possible but not viable.

This project is at the ground stage, but the very idea that experts are working on it is exciting. 

What would such a vehicle mean for mankind? Suppose that we discover a planet that is 100 light years away that might be suitable for us to live on.  We could now get there in a matter of months in 'Earth time'.  The passage of time for our loved ones at home and us will have been about the same.  Mind you, if we wanted to send a message to our family back on Earth about this wonderful new planet, the message would take 100 years to get to them, because electromagetic waves travel at light speed. 

Then again, if there is a work-around for the transport of matter, might there also be one for the transport of information?  Having both of these technologies would potentially extend man's global village into a universal one.

If mankind can avoid destroying itself before this century closes, it appears that some tasty technological treats are in store for it in the one that follows.

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