

Smallest Time Unit
Name: Mitra
Status: other
Grade: N/A
Location: N/A
Country: N/A
Date: 10/31/2005
Question:
What is the smallest unit of time? I have read that the
smallest unit of time is "the time taken for light to travel across the
surface of a speck of dust (that is visible in a shaft of light coming
through a crack in the door of a dark room) that floats in the air". How
can this be a repeatable measure?
Replies:
Dear Mitra,
You are very perceptive to note that the time taken for light "to cross a
speck of dust" is not a repeatable measure.
In fact, as far as is known today, there is no smallest unit of time. A
clear indication of this is that the universe expanded by a larger factor in
the first 1E35 seconds of its existence that it has in the billions of
years since that incredible time. If this is true (and there is actually
pretty good evidence that it is), the smallest unit of time must be MUCH
shorter than 1E35 seconds. By 1E35 I, of course, mean a number which can
be written as 0.000...0001 with 34 zeroes between the decimal point and the
digit 1.
I hope these comments are of some use to you. You are asking about a very
subtle part of our understanding (or lack of understanding). Perhaps
someday we will discover that time is indeed quantized (with the smallest
quantum of time much shorter than 1E35 seconds) and our understanding of
our universe will be much increased.
Best, Dick Plano, Professor of Physics emeritus, Rutgers University
The smallest units of physical variables  time, length, charge, etc. are
based on the value of a few fundamental constants: the speed of light in a
vacuum, Planck's constant, the universal gravitational constant, the
Coulomb force constant and Boltzmann's constant. The web sites below
explain
the Planck time specifically and the origin of the units in general. Other
web sites can be found using a "Google" search on the phrase "Planck
units".
In "Planck units" all these constants equal unity. In SI units the Planck
time is about 5.4x10^44 sec, the Planck length is about 1.6x1035 meters,
2.2x10^8kg, the Planck charge is about 1.9x10^18 coulombs, and the Planck
temperature is about
1.4x1032 kelvins.
http://en.wikipedia.org/wiki/Planck_time
http://en.wikipedia.org/wiki/Planck_units
A detailed discussion of the subject can be found at:
http://hyperphysics.phyastr.gsu.edu/hbase/astro/planck.html
The laws of physics, as we know them, do not apply to values of the
constants smaller than the Planck values.
Vince Calder
Click here to return to the Physics Archives
 
Update: June 2012

