Is there a minimal measurement of time?

[Nacelunk]

Is there a minimal "portion" of time? Or the time can be "divided" on infinite number of parts?

[ecoli]

yes, you can always cut a unit of time in half... at least mathematically

[Nacelunk]

But I mean - really, physically.

[ecoli]

But I mean - really, physically.

 

technically yes... but because the neurons in our brains fire relatively slow, we can't really percieve time on a really small scale.

[Nacelunk]

OK, then. A little off-topic - how about length measurement? Is there anything smaller than electrons, protons and neutrons?

[ecoli]

OK, then. A little off-topic - how about length measurement? Is there anything smaller than electrons, protons and neutrons?

 

string theory postulates the universe is make up of tiny, one dimensional strings. But there's no proof, it's just math.

[insane_alien]

well legnths smaller than the planck legnth technically don't make any physical sense so you could say thats the smallest unit of legnth. just google up planck units

[abskebabs]

Could it be considered therefore that space is discrete and discontinous(at some fundamental level), but time is continous, or is this an unfair assumption? Personally, I wouldn't be so sure because aren't both dimensions mean't to be intimately linked?

[ecoli]

Could it be considered therefore that space is discrete and discontinous(at some fundamental level), but time is continous, or is this an unfair assumption? Personally, I wouldn't be so sure because aren't both dimensions mean't to be intimately linked?

 

considering string theory is supposed to link relatvity and QM, this is probably a fair assumption. I'm not sure what string theory has to say about time... if it does.

[YT2095]

I think the atto second is about the smallest of usable units of time (10^-18).

I stand to be corrected tho.

[timo]

Could it be considered therefore that space is discrete and discontinous(at some fundamental level), but time is continous, or is this an unfair assumption?

Perhaps not an unfair assumption but it seems it would violate special relativity. What happens when you go to another coordinate system where the old time-direction now is a mixture of a time- and space-direction? You get a mixture of discrete and continuous steps, at least in the naive form I am having in mind right now. Therefore you´d have a certain coodinate system which qualitatively differs from all others (namely by that there is no mixture of continuity and discontinuity in the time-coordinate).

But of course we´re talking about extreme regions (small distances) which cannot be probed and it´s hypothetically possible that special relativity (or any other well-proven physical theory) won´t hold true in these regions. After all, that´s why people let their imaginations run loose there - less risk of being caught by hard facts.

 

As for the discrete spacetime in general: In mainstream physics, spacetime is considered contiuous. Afaik, some approaches (namely lattice gauge theories) use a semi-discrete spacetime. By that, I mean doing a calculation in a discrete spacetime (to avoid problematic integrations, I´d guess) but take the limit of stepsize zero (-> continuous spacetime) for the final result. But I´m not even sure where I have this idea from .

[5614]

Is there a minimal "portion" of time? Or the time can be "divided" on infinite number of parts?

The smallest unit of time is the Planck time. It is equal (approx) to [math]{5.4} \times 10^{-44}[/math] although sometimes, as seen here:

http://scienceworld.wolfram.com/physics/PlanckTime.html

a second value [math]\times 10^{-43}[/math] can be obtained using [math]h[/math] inestead of [math]\hbar[/math]... surely there should only be one value? Which one is correct?

 

Also see here (incl. Planck Length): http://en.wikipedia.org/wiki/Planck_units#Base_Planck_units

[swansont]

well legnths smaller than the planck legnth technically don't make any physical sense so you could say thats the smallest unit of legnth. just google up planck units

 

I think "don't make physical sense under current theories" is a little more accurate. The Planck scale is where current theories fail, because we do not have a quantum theory of gravity. So we don't really know what happens at a Planck length. Since this is of order 10^-35m, AFAIK it's not likely we will find out anytime soon either.

[5614]

I think "don't make physical sense under current theories" is a little more accurate.

Can you please expand on that.

 

I know that current theories fall apart due to the lack of a quantum theory of gravity. Going back to the first instances after the big bang when the universe existed on a Planck scale gravity would have a big effect due to the density... but now if we neglect gravity on an atomic scale, because the effects are negligible, surely we can on a Planck scale?

 

Thinking about it, on Planck scales quantum effects become very important, so can we say so must quantum gravity? But it is so weak, does it have any effect on that scale? I almost expect the answer to be yes, but that's weird how gravity effects Planck scales, not atomic scales and then it's back in again at larger (incl. everyday to universal) scales.

[Daecon]

Nope, the smallest unit of time is the Planck unit.

Anything shorter than that and it's not possible to tell (of two events) which happened first.

Time, like space, is "digital".

[timo]

Nope' date=' the smallest unit of time is the Planck unit.

Anything shorter than that and it's not possible to tell (of two events) which happened first.[/quote']

Why?

[swansont]

Can you please expand on that.

 

I know that current theories fall apart due to the lack of a quantum theory of gravity.

 

And that's as far as you can really go. Until we have those theories, we can't intelligently address the question.

[Daecon]

Why?

I forget the exact scientific reasoning, but it may have something to do with quantumn uncertainty...?

 

Or possibly just because for all intents and purposes, anything that happens within a Planck period happens at the same time.

 

I think the analogy of time being a line (One-Dimensional), and a (Planck) moment being a single point on that line (Zero-Dimensional).

 

Anything that is 0-dimensional will always be 0-dimensional, no matter how many of them you put together, or line up side by side, kinda thing.

 

Does that help clarify matters...?

[ecoli]

Nope' date=' the smallest unit of time is the Planck unit.

Anything shorter than that and it's not possible to tell (of two events) which happened first.[/quote']

 

time can only be represented mathematically, if it's smaller then that.

[5614]

And that's as far as you can really go. Until we have those theories, we can't intelligently address the question.

But why? If gravity is safely neglected at atomic scales surely it can totaly neglected at Planck scales?

 

I know that is wrong, because at that scale quantum effects (incl. quantum gravity) play major roles... but how can such a small force like gravity play any effect at such small levels?

[timo]

I forget the exact scientific reasoning, but it may have something to do with quantumn uncertainty...?

I´ve seen that claim quite often. It´s just that I don´t understand it.

 

Or possibly just because for all intents and purposes, anything that happens within a Planck period happens at the same time.

Same is true for a year in geology. But I still know that 2005 came before 2006.

 

I think the analogy of time being a line (One-Dimensional), and a (Planck) moment being a single point on that line (Zero-Dimensional).

 

Anything that is 0-dimensional will always be 0-dimensional, no matter how many of them you put together, or line up side by side, kinda thing.

A line (1D) is commonly believed to be made out of points (0D). Planck time would be an interval on the line not a point, anyways. You can multiply the Planck time by a finite number to get 1 second. But you cannot take a finite number of points to get a line of length 1 cm.

 

Does that help clarify matters...?

No, not really.

[Daecon]

Okay, sorry.

 

Just trying to help.

[timo]

Okay' date=' sorry.

 

Just trying to help.[/quote']

No need to be sorry. I simply don´t understand the statement that at Planck distance/time physical laws break down. So please don´t mistake any criticism or repeated "I don´t undestand what you are saying" as a personal attack. It´s just that I don´t think lying I´d understand the statement just to be gentle would do any good.

[Ragib]

There is no evidence of a minimal portion of time, but there is a minimal portion of measurable time, that is, what we can physically measure to an accuracy to, even theoretically. abskebabs, is space is quantizes, so is time, also though have no proof to prove right or wrong. Only measurable limits. YT2095, the smallest unit of time, The Plank Time, 5.391 × 10^−44 seconds. It is C/THe plank Length, which is 1.61624 × 10^-35 m.

 

Originally Posted by Transdecimal

Nope, the smallest unit of time is the Planck unit.

Anything shorter than that and it's not possible to tell (of two events) which happened first.

 

The smallest unit of time MEASURABLE is the Plank time, according to Quantum Mechanics. By Quantum Mechanics its not possible to determine which event happened first. However, maybe string theory will shed some light on the matter. Its not known if time is truly quantized.

 

Atheist, when Transdecimal Said it is due to Quantum Uncertainty, hes talking about Heisenbergs Uncertainty Principle. One of the equations - . It is impossible to know the Energy of something precisely, with prefect accuracy of time as well. The Delta Triangles means uncertainty in measurment in this case. If you dont know the energy transfers, you dont know the event happened. So you can only tell an event happened assigned to a time, with a limited amount of accuracy. That is what quantum mechanics says. There are many different interpretations of this effect, some say this inaccuracy is due to the fact measuring it involves observing it, collapsing its wavefunction and therefore affecting the outcome. Some others say its a fundamental inaccuracy in nature. If you have any more questions please ask.

[Ragib]

Btw, dont worry if you don't like the idea of Quantum mechanics in general, with the probabilities and no determinism..Eienstein didnt like it either, He and I and many others think theres a more fundamental theory that will replace QM and explain this effect.