# Universal unit of time

1. Sep 2, 2007

### teleport

The title might be a little ambiguous since I do not mean to talk about time curvature. I am interested in some non-technical explanation, in some historical context, of past and current knowledge/research (if there ever was) regarding the possibility that the time line might be entirely composed of discrete values, that is, that time might not be continuous, implying there is a smallest universal unit of time or atoms of time. I know that there is really no reason to think like this, but I am just wondering if this thought has ever occurred in physics literature.Thanks!

I wasn't really sure to what forum type this subject might belong to. I chose this because I thought that 'discretness of time' might pertain to quanta.

2. Sep 2, 2007

### bel

Yes, in fact, there is what is called the Planck time, which is the theoretical limit of measurable, and hence meaningful time. It is the time taken for a photon to travel one Planck length of a distance.

3. Sep 2, 2007

### teleport

OMG that is so interesting. Now I have more questions. Is this Planck time accepted by the scientific community? So you can not measure time below this limit? So we can't know if time expands or remains constant in this Planck length of distance? But if time remains still for a photon crossing this distance, then doesn't it mean that the photon does actually jump this distance, the next TIME you look at it? So that means that space is also discrete? OMG!

4. Sep 2, 2007

### ganstaman

Assuming I'm not confused enough, space would also be discrete, with cubic Planck lengths being the units. Hmmm, something about that doesn't sound right. How about this -- nothing can move less than a Planck length in distance, and all straight-line motion through space must be in multiples of the Planck length.

We're not even close to measuring things this small, so direct proof may not be possible. There may be some theoretical implications of this that can be tested, however.

In case I'm wrong up there, I believe that this is at least correct: Our current understanding of physics breaks down at lengths smaller than the Planck length and times smaller than the Planck time. So even if space and time were more divisible (not discrete), the laws of physics as we know them seem not to operate in these smaller divisions, so envisioning the fabric of space-time in these discrete units is very practical.

5. Sep 2, 2007

### teleport

Well, if I could walk though this Planck distance (and somehow someone would notice), then the world would know I travel faster than the speed of light. Makes sense.

6. Sep 2, 2007

### teleport

What you say makes complete sense but still reminds me of the incompatibility of Newtonian laws at the quantum sizes. Perhaps there is a similarity here. But I do understand that until measurments can be made at this level, no one can say that our mathematical representaions of physics are incomplete or otherwise.