now
the plank length is as we know the
smallest length but is there a smallest
time scale like something smaller than
nanoseconds
yes yes you take the plank length it's a
length
it's much smaller than my hand and you
divide it by the speed of light well is
is it really the smallest interval of
time i mean we don't know that but if we
wanted to construct a very short
interval of time
from the planck length we would just
take the plank length of 10 to the minus
35 meters and divide by the speed of
light which is 3 times 10 to the 8
meters per second and lo and behold if
we do that division we'll get the planck
time which is something like 10 to the
minus 43 seconds and that is meant to be
the time
after which the big bang has gone into
the realm of physics that we know
according to most people's beliefs
because you really can't test that out
no one can measure it of course it's so
far
so much smaller than the pla nano scale
i think the the the shortest time
interval that people have been able to
measure is called an atos i think it's
an ato second it's about 10 to the minus
18 of a second so this is way smaller
than that so the planck time
before that
there's a big bang plank length of time
and then after that laws of physics are
as we know it we don't know what
happened before
now what is the significance of that
time well i think the most significant
aspect of it is that uh we certainly
haven't got any idea of what physics is
like at that length scale or time scale
so that's something about the this idea
of the foaminess of
of of space and time it would be down on
that length scale and it's got something
to do with
some physics we don't understand
involving quantum mechanics and gravity
so what's its use it's its use is
primarily in theories in the sense of
trying to understand when you might
expect um
quantum gravity effects to have to come
into place when we need to really
understand how to quantize gravity at
the moment we don't really understand
that we have models to try and do it but
so we're happy to push models using
classical gravity down to about that
scale although we probably shouldn't
but i think most people at that scale
would throw their hands up in the air
and say we don't know what's going on we
we need to have a proper quantum theory
of gravity