|
Can We
Travel Faster Than Light? - Page 2
Physicist Thomas
Roman of Central Connecticut State University offers the
following response:
|
WORMHOLE. If nature
allowed them, wormholes would appear as spherical
openings to an otherwise distant part of the cosmos.
This doctored photograph shows a wormhole in Times
Square that opens onto the Sahara Desert one city
block away. |
|
In the pre-Einsteinian conception of the nature of
space and time, there is no limit in principle to how
fast an object can travel. But in Einstein's special
theory of relativity, the notion of causality--of the
past completely determining the future--would break
down if any type of matter, energy or signal were able
to travel faster than light.
In the pre-Einsteinian framework, time has an absolute
character. The time of an event--and thus its time ordering--is
the same to all observers; velocities add according
to ordinary addition. For very small velocities (small
compared to the velocity of light), the same holds in
relativity, but for large velocities significant modifications
occur. Early in the 20th century the Michelson-Morley
experiment established that the speed of light is the
same to all observers whatever their relative motion.
|
Therefore the law for adding velocities must
be modified. The relative velocity of two objects, one traveling
at the same of light and the other traveling at sublight speeds,
must equal the speed of light. When both are traveling at
sublight speeds, the relative velocity must be less than the
speed of light.
One surprising consequence is
that time loses its absolute character. The times perceived
by observers moving with respect to each other do not coincide.
But observers always agree on the ordering of events. If we
admit the possibility of faster-than-light speeds, some observers
would perceive one event as occurring before another, others
would perceive them as occurring simultaneously, and a third
group would perceive the reverse order. The time ordering
is invariant only when the two events can be linked by a signal
traveling at a speed slower than or equal to the speed of
light.
In the context of an expanding
universe, it is often stated that widely separated points
move apart faster than the speed of light. At first sight
this would seem impossible. But an expanding universe must
be considered within Einstein's general theory of relativity,
a generalization of the special theory of relativity. In general
relativity, motion relative to the speed of light is defined
locally. The separation between two distant points can increase
faster than the speed of light as a result of the swelling
of the intervening spacetime. Nothing can pass through the
space faster than light, but space itself can carry things
apart superluminally.
Back
To Science
|
|