# [FOM] Infinitely divisible spacetime?

tr5374 tr5374 at albany.edu
Sun Sep 4 17:26:20 EDT 2016

```On Thu, 1 Sep 2016, Stephen Paul King wrote:
. . .
> â€‹  I have often wondered why the common perception you mention persists...
> The Planck â€‹constant and the associated "scale" is a limit on the ability
> to measure, not on what is. Many have written on the problem of reconciling
> GR and QM and tried to argue for some kind of granularity of space-time,
> but that only aggravates the problems.
. . .

Happening to be working on some questions of time, I just read something
relevant to this discussion and so will pass it along here.  It is from
late 2004, and both authors were at NIST, Scott Diddams and Tom O'Brian.
O'Brian is now Chief of the National Institute of Standards and
Technology's (NIST's) Quantum Physics Division, and also heads the Time
and Frequency Division at NIST-Boulder, so I suppose it counts as
reasonably authorative.  The URL is
http://www.scientificamerican.com/article/what-is-the-fastest-event/

<quote>
The question of whether there is a limit to how short a time interval
could conceivably be measured gets to the heart of complex and currently
untestable theories about space, time and energy. A short and incomplete
answer is: "No one knows for sure if there is a limit to how finely time
can divided and measured. But accepted current theories suggest that
there are limits to how finely time could be measured." There is of
course no limit to how small a time interval we could conceive, but if
present understandings of the nature of time, space and energy are
correct, there would be insurmountable limits to measuring time
intervals.  Most current theories of the universe hold that time, space,
and energy all become intertwined at very short time intervals and over
very short distances, for which energy becomes very great. This apparent
limit on time interval is about 10^-43 second and is called Planck time.
The Planck distance--how far light travels in one unit of Planck
time--is about 10^-35 meters, or about 10^20 times smaller than the size
of the nucleus of an atom. ... [I]t generally takes more and more energy
to probe physical events on shorter and shorter time scales.  Inferring
the top quark lifetime requires the most powerful particle accelerators
in the world, and these extremely high-energy events are still about
10^20 times weaker than the energies that would be required to observe
events on the scale of Planck time.
</quote>

Cheers.
Thomas Reynolds
```