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]

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]

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]

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..]

[maddog]

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

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.

By SR, a particle with mass moving slower than light would not exceed c. To do so it's mass and sense of

time would transform into a complex number (imaginary). Most physicists I have met will tell you this is

"not possible". However, even Einstein did not say tachyons (particles already moving faster than c)

could not exist; he said he "couldn't imagine it". A pun really. To move faster than c in the same spactime

as light itself would need to have imaginary mass and imaginary time and negative energy.

... 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.

This is consistent with SR, it is the snap and disappear that is writer's license and conjecture. ;)

 

Maddog

[alxian]

thats what i think they got right though, not that we'd still 'see' it resting and stretching into hypervelocity, but that it would simultaneously exist temporarily here there and in between, if you could 'see' that you'd see it 'snap' but the disappear part is misleadnig, what you'd see is the last flicker of light on it before it exceeds c, once beyond c [which should be instantly] no light would be able to reflect off of the object, any light it emmit will show though.. so in keeping with sci-fi the nacell glow would persist momentarily then once the source ends up 'there' you wouldn't 'see' anything.. a startled alien culture along the route might puzzle momentarily as to the instant red streak of the nacells [of the enterprise in this example]. what you'd 'see' if you could observe the translocation is all the light escaping the craft as it temporarily would be stretched across its intended course.. a blurred line at anypoint would be equal to the escaping light of the craft.

 

question two is: how do you stop?

 

i always thought instantly stopping was as ludicrous as instantly starting.. but don't dimiss either simply that kinetic energy once the potential is released is hard to harness.

[Buffy]

question two is: how do you stop?

 

i always thought instantly stopping was as ludicrous as instantly starting.. but don't dimiss either simply that kinetic energy once the potential is released is hard to harness.

Stopping is always the same physics probem as starting: got to use friction or mass accelleration with the right vectors, unless theres a new mechanism invented, which would probably be necessary anyway to make the quantum jump across c to keep from having your mass go "infinite." "Instant" starting and stopping, well, that can be problematic. Star Trek "invented" the "inertial damper" which keeps your intestines in place as you go from zero to warp 5 in sub-5-second quarter-parsecs (and that's a *lot* of horsepower!).

 

Now one of the things that the StarTrek folks came up after talking to people who knew their stuff (remember, Harlan Ellison wrote several original scripts) was the notion that to get around the "imaginary number" problem that pops up in the equations as Maddog has pointed out, those numbers go "non-imaginary" again once you get past 2c (call me on this, this is second hand to me and I have *not* done the math), so "going warp" would entail not only jumping over c but all the way up to 2c so the weird effects (going back in time, having a mass measured in ci+n notation), would "go away." Entirely speculation of course....

 

Cheers,

Buffy

[maddog]

Now one of the things that the StarTrek folks came up after talking to people who knew their stuff (remember, Harlan Ellison wrote several original scripts) was the notion that to get around the "imaginary number" problem that pops up in the equations as Maddog has pointed out, those numbers go "non-imaginary" again once you get past 2c (call me on this, this is second hand to me and I have *not* done the math), so "going warp" would entail not only jumping over c but all the way up to 2c so the weird effects (going back in time, having a mass measured in ci+n notation), would "go away." Entirely speculation of course....

You asked me to call you on it, so I will. :o This is not a circle thing like 2pi or anything. From a speed

greater than c to infinity, time, mass (for a particle with mass) would be multiplied by i (sqrt(-1)) to make

SR Lorentz equations balance. This implies the Star Trek notion of FTL travel is a bit inventive yet off.

The best book I saw on the subject (forget author) is "The Physics of Star Trek". I found it quite informative.

I'm all for speculation. I do a lot of it myself. It just needs to bear fruit with the facts to merit. :o

 

Maddog

[alxian]

i still think though that infinite mass is more relative to infinite inertia, meaning the mass never changes only the amount of energy required to overcome that nearly insurmountable inertia of matter travelling at superluminous speeds would mean that object will not diverge easily from its plotted path.

 

although if light bends around massive objects would matter bend more? or not at all?

 

if you can impart/dissipate artificial inertia you could get instantaneous starting and stopping.. i wonder if a way can be found to transfer inertia cleanly from a gyroscopic partical to a stationary one in such a way as to make that stationary partical move in one unique controlled vector. technically speaking if you can get that gyroscopic partical to spin incredibly fast* and then overcome its spin and transfer that kinetic spin into one vector (the whole ship in fact would have to move from that spin state to vector state without destroying itself) you could move around as you pleased.. on a timer if you forget to watch the controls..

 

*can a spinning object exceed c?

[maddog]

i still think though that infinite mass is more relative to infinite inertia, meaning the mass never changes only the amount of energy required to overcome that nearly insurmountable inertia of matter travelling at superluminous speeds would mean that object will not diverge easily from its plotted path.

Would need to exceed infinity (impossible) to smoothly exceed c (from below).

although if light bends around massive objects would matter bend more? or not at all?

Have you studied Differential Geometry ? If so you would understand that Reimannian Geometry shows

the space to being bent. So whatever is in motion is bent in the same fashion and if large enough its

structure would bent in the same method.

can a spinning object exceed c?

Rotational speed has the same boundry as linear speed wrt c. However, there are interesting effects as

a rotational speed approaches c. I believe it is called the Turrell effect (close). Google on it. Have fun. :o

 

Maddog

[Tormod]

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

 

We actually discussed this not too long ago in this thread: