Some people refer to relativity as the "law of relativity" (sometimes
in the same document that they call it the "theory of relativity").
Similarly, some appear to treat the view that time flows only in one
direction as a law. However, the truth of these matters is not so
certain in this post-Einstein world.
A scientist first comes up with a hypothesis, a tentative explanation
for a set of observations. If the hypothesis is tested and confirmed
in many situations, it may be called a theory. If the theory always
holds true for certain circumstances, and is accepted by the general
scientific community, it may be called a law. Examples are the law of
gravity and Mendel's laws of heredity.
"Scientific Hypothesis, Theories and Laws" (Evolution for Teaching,
The School of Science and Engineering)
The University of Waikato
"Scientific laws" (Ask A Scientist, Biology Archive)
"Scientific Laws, Hypotheses, and Theories"
If one believes that Einstein theory of relativity has stood the test
of time and experimentation, one might decide that it's a law.
However, I believe that you are correct that relativity is more
generally referred to as "theory." The following article explains
that relativity is indeed a theory and not a law:
"The scientific method - how science proceeds from theory to law," by
Timothy F. Ball
Einstein is often cited as saying something like, "Time is an
illusion" (or "Reality is an illusion"). Certainly, Einstein is
partially responsible for this view. Moreover, Einstein did say
something closely similar when he wrote, "The distinction between
past, present and future is an illusion, however persistent." (Oxford
Dictionary of Quotations, ed. Elizabeth Knowles (5th ed. 1999), p.
291.) He didn't exactly say that time itself is an illusion, but that
distinctions between different conventional categories of time are.
My sense is that scientists have not found laws for time; at best they
have theories, like relativity, along with hypotheses. An indication
of the uncertainty about time is a recent paper, by a previously
unheralded college dropout named Peter Lynds, which "rocked the
physics world - and the space-time continuum."
"Time's Up, Einstein," by Josh McHugh (June 2005)
Until there are generally accepted laws of time, I don't believe we
can say for certain whether things can move only forward in time, or
both forward and backward under certain circumstances -- or whether
time is an illusion. As one researcher puts it:
"Is time real? Does it flow in one direction only? Does it have a
beginning or an end? What is eternity? None of these questions can
be answered to scientists' satisfaction. Yet the mere asking of these
questions stretches our minds, and the continual search for answers
provides useful insights along the way."
"Traveling Through Time," by Clifford Pickover (Updated November 2000)
As the recent Wired article explains, Einstein thought that time could
go faster, slower, or backward, depending on your point of view, while
Lynds is trying to show that time is truly an illusion. But unless
and until time is proven an illusion, the most interesting question --
at least for those fascinated by the possibility of time travel --
might be whether things (including people) can go backwards in time.
Here is an article that considers time travel, both forwards and
"A User's Guide to Time Travel," by Michio Kaku (August 2003)
For more comprehensive discussions about time and time travel,
including material about relativity, see:
"The Nature of Time" (Created Feb. 25, 2005)
"Everything you always wanted to know about ... Time Travel"
Search strategy --
Searched on on Google for various combinations of these terms:
"theory of relativity"
"theory of * relativity"
"law of relativity"
"law of * relativity"