# Q & A: speed of time?

Q:
I have not been able to find any information on the speed of time (speed of events). Has anyone ever came up with a formula to calculate the speed of time, and also a way to isolate a single point in time?
- Mike (age 23)
Texas
A:
I don't really think it makes sense to ask about 'the speed of time'. What we mean by speed is how much of something happens per time increment. Whatever units you choose to measure time in (seconds, years, etc) it takes just one of those units for one of those units to occur.
The only speeds that have meaning are the comparisons of two different rates- say how many periods of the light coming from a He-Ne laser occur during one heartbeat, etc. Much of phyics, chemistry, and biology are devoted to figuring out such comparative speeds, so there's no one simple formula to cover the whole lot.

Your other question is about isolating a single point in time. In general,there are different ways of taking slices through all the events in space-time to get different collections that you say are 'simultaneous'. None of these slices are any more or less true. So there are problems trying to define a single point in time, unless you also mean at a single point in space. There are other problems with that too, but probably that's enough nay-saying for now.

Mike W.

(published on 10/22/2007)

## Follow-Up #1: Is there a smallest time interval?

Q:
Can time be sliced into such a smallest slice that no event can be packed in a slice smaller than this. I mean to say whether time is continuous or discreet?
- Indrajit
New Delhi, India
A:
Not that we know of.  There is, however, a time interval called the Plank time that is derived from the fundamental constants: h, Plank's constant,  G, the gravitational constant, and c, the speed of light.  The number you get is ridiculously small, ~5 10-44 seconds.

Does our picture of spacetime fall apart on that scale? One experimental test has been tried. It was conjectured  that far away images would be blurred by space-time foam fluctuations on the order of the Planck scale. An astronomical experiment using the Hubble deep field images produced an equivocal result.  So in sum, there is no convincing experimental evidence for a smallest time interval.   See:   for some information.

LeeH

(published on 06/21/2010)