Plank unit for time

[pgrmdave]

If there is a minimum amount of movement within a spatial dimension, is there a minimum amount of movememt within a time dimension? What would this mean, both philosophically, and scientifically?

[Buffy]

Yep. "Planck Time" See: http://en.wikipedia.org/wiki/Planck_time ...

Cheers,
Buffy

[The Heretic]

I would suppose that, philosophically, Planck time represents the limits of physics. Once you get smaller/shorter than Planck units, the theories break down.

[Tormod]

I don't think it's quite correct to say the theories break down. Classical physics did not break down when quantum physics entered the stage. Rather, the planck time is a prediction in quantum physics and (just as planck length) and as such is not verifiable by observation but only by calculation. It is a definition more than an actual thing.

BTW, the planck time is defined as the time it takes a photon to travel the planck length, and is supposed to be 10^-42 seconds.

This also implies that when the Universe was born, it was already 10^-42 seconds old already.

[The Heretic]

Perhaps i was being a bit hasty with my word choices, Tormod. By "breaking down" i mean the theories no longer apply once the object of inquiry is smaller or shorter than the Planck units.

That could possibly mean there is nothing smaller or shorter than any planck unit, and to posit such an entity is foolhardy.

[Tormod]

I didn't mean to correct you, just pose another view!

I see a problem in the above definition. If the planck length is the minimum length...then how can a photon traverse it? Nothing can travel along a plack length, because it is the minimum quanta. If something could travel, say, a half plank length then there you go - another minimum length.

The plack time sounds like it is based on a theoretical construct which is flawed. I may have to read up on this a bit...

I have read a few interesting articles in New Scientist about what happens to spacetime at the planck length. It supposedly turns foamlike and has strange properties. Very interesting stuff but hard to grasp, really.

[lindagarrette]

Originally Posted by Tormod

I didn't mean to correct you, just pose another view!

I see a problem in the above definition. If the planck length is the minimum length...then how can a photon traverse it? Nothing can travel along a plack length, because it is the minimum quanta. If something could travel, say, a half plank length then there you go - another minimum length.

The plack time sounds like it is based on a theoretical construct which is flawed. I may have to read up on this a bit...

I have read a few interesting articles in New Scientist about what happens to spacetime at the planck length. It supposedly turns foamlike and has strange properties. Very interesting stuff but hard to grasp, really.

I tend to agree with you, Tormod, although supposedly, anything can be subdivided infinitely. Scientistst insist on setting a real number value to planck time based on length and the speed of light.

Planck time
In quantum mechanics, the shortest meaningful period of time; any two events that are separated by less than this amount of time can be considered simultaneous. It has the value 5.390×10-44 second. Related to this is the Planck length of 6.160×10-35 meters, which is the distance that light can travel in the Planck time.

[Fishteacher73]

Originally Posted by lindagarrette

Planck time[/size][/b] [/size][/size][/font]
In quantum mechanics, the shortest meaningful period of time; any two events that are separated by less than this amount of time can be considered simultaneous. It has the value 5.390×10-44 second. Related to this is the Planck length of 6.160×10-35 meters, which is the distance that light can travel in the Planck time.

Isn't this a bit of a circular definition. Much like work is the use of energy and energy is the ability to do work?

[Buffy]

Originally Posted by Fishteacher73

Isn't this a bit of a circular definition. Much like work is the use of energy and energy is the ability to do work?

Sorta, but its okay because they're both based on Planck's constant, which is then combined with the speed of light (c, which of course is also a constant), to get both a distance and a time. So its basically like saying I can get from here to San Jose by driving for 40 minutes or by driving for 60 miles (okay, I drive fast. Don't tell the CHP...).

Cheers,
Buffy

[alxian]

what happens though when you exceed c.. by theory i abhor i understand that you arrive before you left.

which bugs me because once you exceed c you still haven't actually gotten there yet, what you have done is travelled faster than we can measure physically (by measuring your position based on your last know position).. you'll still be travelling, you'll just get there faster. you'll eventually get there instantly (by all available metrics) my question was always if you can travel instantly from here to there and nothing crosses your path during your passage are you occupying all of the space for all intents and purposes between here and there? or are you simply exceeding our metrics of speed and distance and infact do travel contiguously from here to there without beeing everywhere in between during your transit. while of course the confusion only arrises if you believe that there is an ultimate speed limit.

for an example, again quoting sci-fi, whenever you see anything move faster than is possible you'll 'see' it stretch, so for all intents and purposes (relative to all matter nearby) the object moving instantly from here to there will seem the stretch the entire distance, in one instant it is here,[tick off one planck time increment] the other it is here there and everywhere in between, [tick off another planck time increment], its there, but remains contiguous the whole way from here to there. otherwise the only instantineity theories available would have you believe that its never at any time 'in the middle', only here then there, which bugs me. [i like continuity, translocation, preservation, anything else is uncivilized..]