Exploring the Concept of Time: Limitations and Possibilities

[cheemaftw]

Before reading this, please note that my knowledge of physics at this time is quite poor as I'm only 15.

Time is only measurable when relative to a progression/regression of something. Therefore, the limit to which we can measure time depends on the shortest possible progression/regression. Because time = distance/speed, the shortest time must be one that is over the shortest distance possible and at the fastest speed. The shortest possible length possible is the Planck length and the fastest possible speed is the speed of light. Therefore, because time only "exists" when measured relative to a progression or regression, the shortest possible time is defined as: ℓP/c = 1.616199 × 10^-35/m / 299 792 458 m/s.

I'm probably completely wrong about this, just some thoughts. I'd appreciate any feedback on where I went wrong, and why.

Thanks

 

[bcrowell]

Welcome to PF!

The time you've defined is known as the Planck time. There are a bunch of different "Planck" things defined in this way, including a Planck mass and a Planck energy.

The real question is whether it's valid to call the Planck length the shortest possible length. If that was valid, then it would certainly be true that the Planck time was the shortest possible time.

Well, we don't have a theory of quantum gravity, so nobody really knows the answer to this for sure. However, it seems unlikely that a theory of quantum gravity would have a minimum length. The reason is that according to special relativity, an observer moving relative to an object sees it as length contracted. So if the object had the minimum length in its own rest frame, it would seem to have less than the minimum length to the observer moving relative to it.

 

[cheemaftw]

Welcome to PF!

The time you've defined is known as the Planck time. There are a bunch of different "Planck" things defined in this way, including a Planck mass and a Planck energy.

The real question is whether it's valid to call the Planck length the shortest possible length. If that was valid, then it would certainly be true that the Planck time was the shortest possible time.

Well, we don't have a theory of quantum gravity, so nobody really knows the answer to this for sure. However, it seems unlikely that a theory of quantum gravity would have a minimum length. The reason is that according to special relativity, an observer moving relative to an object sees it as length contracted. So if the object had the minimum length in its own rest frame, it would seem to have less than the minimum length to the observer moving relative to it.

Thanks for the welcome and quick reply :)
So what's the purpose of the Planck length? Is it widely disregarded now?

 

[espen180]

The Planck units are units chosen such that certain dimensionful constants: [itex]c\,,\, \hbar \,,\, G \,,\, (4\pi\epsilon)^{-1} \,,\, k_B[\/itex] (speed of light, reduced Planck's constant, the gravitational (Newton's) constant, and Boltzmann's constant) all have numerical value 1 when expressed in those units. This makes a lot of physical formulae simpler by eliminating meaningless constants (look up nondimensionalization).

I think the reason people think/thought that they were related to a possible theory of QG is that each of those constants is associated with a paticular physical theory (relativity, QM, gravity, EM, thermodynamics), making the unit system attractive for unification theories.

All this is written on the wikipedia page: http://en.wikipedia.org/wiki/Planck_units

 

[BrettJimison]

I lean more towards time NOT being quantized. I believe scientists are accurate in saying energy and speed can be quantized, but not time.
Why?
First off: I like to think time is a "man made" thing. We observe repetition, and we can count repetition to see how much "time" has passed. Obviously it stated with just the sun and moon, and has progressed to atomic clocks counting the vibrations of excited cesium atoms.( A very accurate way to measure a second is to count 9,192,631,770 cycles of an excited cesium atom), but in the end its all repetition.
With that being said, why do I think time isn't quantized?
Even though energy may be quantized, it does not mean time is quantized. Its rather abstract, but the simplest way to put it is: Even though energy jumps to certain states, and jumps back (not existing at all in the space between the two states) does not mean time jumps with it.
Another way to put it is this: Let's say Planks constant is WAY bigger than it really is (lets say 6.676X10^-10) obviously the cycles in nature would seem more "choppy", and energy would flow less smoothly, but the time between energy jumps would not change at all, even though energy would flow in bigger "chunks"...this is also a hard concept to explain! I like to think time is an illusion we made up, of a way to organize events we experience.

 

[BrettJimison]

Another good example if time being an illusion:

Consider Einsteins Relativity - the faster you move through space, the slower you move through time. When in reality you are really moving through time at all (as if its some medium) but rather, the atomic processes which we use to count repetition slow down. If you were to "time travel" in Einsteins Universe, by moving close to the speed of light, someone on Earth could (theoretically) still look into a telescope and SEE you moving through space, meaning you would occupy the same "Time" and "Space" that they do, you will just be experiencing it slower then they are. This is just an example to show that time is something completely separated from energy or anything else we can measure/observe.

 

[Meselwulf]

Well, we don't have a theory of quantum gravity, so nobody really knows the answer to this for sure. However, it seems unlikely that a theory of quantum gravity would have a minimum length. The reason is that according to special relativity, an observer moving relative to an object sees it as length contracted. So if the object had the minimum length in its own rest frame, it would seem to have less than the minimum length to the observer moving relative to it.

A paradox in it's own right, however in the context of relativity, it's just a bizarre law. Like how when someone moves at the speed of light, light still travels at the speed of light and one can see them self in the mirror?

 

[Meselwulf]

Time itself could actually be illusion -- more and more scientists today are warming up to this idea and a LOT of this had to do with Julian Barbour's work on timelessness and why it is essential for relativity.

 

[HomogenousCow]

I insist that physics should always be discussed with mathematics.
For example when we talk about the quantization of angular momentum, those of us who are learned in the subject will obviously know that this is a direct consequence of the angular momentum operator having only discrete eigenvalues.
However to one who is not familiar with the real theory (the mathematics), the concept will be baffling and unconvincing.

 

[Meselwulf]

I insist that physics should always be discussed with mathematics.
For example when we talk about the quantization of angular momentum, those of us who are learned in the subject will obviously know that this is a direct consequence of the angular momentum operator having only discrete eigenvalues.
However to one who is not familiar with the real theory (the mathematics), the concept will be baffling and unconvincing.

Well... we could discuss world lines for instance, and how there is no such thing as a past and a future and how time is essentially static?

There is after all, no such thing as a Global Time in relativity.

 

[phinds]

... If you were to "time travel" in Einsteins Universe, by moving close to the speed of light, someone on Earth could (theoretically) still look into a telescope and SEE you moving through space, meaning you would occupy the same "Time" and "Space" that they do, you will just be experiencing it slower then they are ...

That is NOT correct. You will SEE them as experiencing it more slowly than you do but you do NOT have a privileged frame. From their frame of reference, YOU are the one "experiencing" it more slowly. Each of you, in your own frame, is experiencing time at one second per second.

 

[Drakkith]

I lean more towards time NOT being quantized. I believe scientists are accurate in saying energy and speed can be quantized, but not time.
Why?
First off: I like to think time is a "man made" thing. We observe repetition, and we can count repetition to see how much "time" has passed. Obviously it stated with just the sun and moon, and has progressed to atomic clocks counting the vibrations of excited cesium atoms.( A very accurate way to measure a second is to count 9,192,631,770 cycles of an excited cesium atom), but in the end its all repetition.

Things have been happening well before Man ever developed, so I can't see how you can claim that time is man made. How we MEASURE it is, but not whether time is man made or not.

With that being said, why do I think time isn't quantized?
Even though energy may be quantized, it does not mean time is quantized. Its rather abstract, but the simplest way to put it is: Even though energy jumps to certain states, and jumps back (not existing at all in the space between the two states) does not mean time jumps with it.

Energy is not quantized. Photons are quantized, as are certain quantum states, but energy as a whole is not.

Well... we could discuss world lines for instance, and how there is no such thing as a past and a future and how time is essentially static?

There is after all, no such thing as a Global Time in relativity.

I don't follow you. How can you say there is no future or past? Every observer should have a definite past and future, regardless of the rest of the universe, should they not?

 

[Dale]

First off: I like to think time is a "man made" thing. We observe repetition, and we can count repetition to see how much "time" has passed. Obviously it stated with just the sun and moon, and has progressed to atomic clocks counting the vibrations of excited cesium atoms

Nonsense. Do you really believe that no planet ever orbited a star in a repeated fashion until man arrived and made time? Do you honestly think that no cesium atom ever emitted its hyperfine radiation until man arrived? If not, then time is clearly not a man made thing.

The various units of time (1 "year" is the period of one orbit of earth, 1 "second" is 9,192,631,770 periods of the cesium atom radiation) are man made definitions, but time itself is clearly not man made.

How could there even be any repetition for us to observe without time existing?

EDIT: I see Drakkith made essentially the same comment.

 

[BrettJimison]

That's not what I'm saying. I'm saying that when man arrived (whenever we did) we saw repetition as a way of keeping track of events. When did I say that repetition didn't exist before man started counting it? That's obviously nonsense! Read!

Drakkith - Not just photons are quantized, energy as a whole IS Quantized, read the works of Neils Bohr. Electon's energy states themselves are quantized

Phinds- You are correct, I was typing to fast. True, according to relativity, each will view the other as moving slower than the other.

 

[Meselwulf]

That's not what I'm saying. I'm saying that when man arrived (whenever we did) we saw repetition as a way of keeping track of events. When did I say that repetition didn't exist before man started counting it? That's obviously nonsense! Read!

Drakkith - Not just photons are quantized, energy as a whole IS Quantized, read the works of Neils Bohr. Electon's energy states themselves are quantized

Phinds- You are correct, I was typing to fast. True, according to relativity, each will view the other as moving slower than the other.

Time is nothing but clocks, however there is no absolute observer. So where does time originate?

It comes from those who consciously perceive it, not inanimate objects which don't understand it.(That was to Dale) I quoted the wrong post.

 

[Meselwulf]

Sure... time may have existed before man, even though relativity itself has a lot of contradictions on what time is itself. But if time is something which is ''experienced'' then trust me, conscious activity has everything to do with it.

 

[BrettJimison]

Meselwulf - That's exactly what I'm trying to say. You stated it much better than I did!

 

[Meselwulf]

And yes, not only photons are quantized, everything is... at the most fundamental level of course.

 

[Meselwulf]

Meselwulf - That's exactly what I'm trying to say. You stated it much better than I did!

Thank you.

 

[phinds]

Sure... time may have existed before man ...

Really? You really think there is ANY possibility that time just sprang into existence along with man? Which form of man is that by the way? Early hominids? Wall street suits? You REALLY haven't thought this through.

 

[Meselwulf]

You forget, science is not absolute... science in the world we deal with exists as possibilities... probabilities. So... yes. It is possible time existed before any sentient being in this vast universe came into existence.

You don't however seem to have a very good grasp of what time is... for starters, time is local not global. Timelessness exists within the solutions of GR which means... when you quantize the equations of GR you actually find the time derivative of the Hamiltonian describing this universe is uniquely... timeless. It is you sir who hasn't thought this through.

Where does time originate, if not by something which can solve these paradoxes of relativity? Sentient beings experience time pass, things outside the mind... have no care of a second pass.

 

[Meselwulf]

Does an electron care itself whether a second passes?

In fact... a photon according to theory doesn't even experience a second pass, if it had itself a frame of reference, but it doesn't. Our universe is essentially... timeless when you take into account the equations of relativity that is...... you don't take these solutions seriously?

 

[Drakkith]

Drakkith - Not just photons are quantized, energy as a whole IS Quantized, read the works of Neils Bohr. Electon's energy states themselves are quantized

And yes, not only photons are quantized, everything is... at the most fundamental level of course.

So you assert that the kinetic energy of an object is quantized? How about temperature? I don't think I've ever seen anything saying that.

 

[Meselwulf]

Also, you want to talk... ''hominids?''

There are two gene regulators inside the human being which is actually responsible for our sense of time... do you know what they are?

 

[Meselwulf]

So you assert that the kinetic energy of an object is quantized? How about temperature? I don't think I've ever seen anything saying that.

Energy and temperatures are related... what about the background TEMPERATURES OF SPACE?

This is made up of quantized photon energy.

 

[Meselwulf]

The BASIC temperature of a system vibrates at

$$1/2 \hbar \omega$$

 

[Drakkith]

You forget, science is not absolute... science in the world we deal with exists as possibilities... probabilities. So... yes. It is possible time existed before any sentient being in this vast universe came into existence.

I see no reason to think that time has not always been as fundamental as distance in regards to the universe.

You don't however seem to have a very good grasp of what time is... for starters, time is local not global. Timelessness exists within the solutions of GR which means... when you quantize the equations of GR you actually find the time derivative of the Hamiltonian describing this universe is uniquely... timeless. It is you sir who hasn't thought this through.

What are you talking about? We have no reason to quantize time yet.

Where does time originate, if not by something which can solve these paradoxes of relativity? Sentient beings experience time pass, things outside the mind... have no care of a second pass.

Irrelevant. We are not talking about time as a we perceive it, we are talking about time as a physical dimension.

Does an electron care itself whether a second passes?

In fact... a photon according to theory doesn't even experience a second pass, if it had itself a frame of reference, but it doesn't. Our universe is essentially... timeless when you take into account the equations of relativity that is...


... you don't take these solutions seriously?

No, our universe is not timeless. A ticking clock immediately invalidates your statement. The equations of relativity do not tell us that the universe is timeless. If you wish to claim otherwise please provide a mathematical example in support of your position.

 

[phinds]

Also, you want to talk... ''hominids?''

There are two gene regulators inside the human being which is actually responsible for our sense of time... do you know what they are?

No, nor do I care. Your apparent assertion that time did not exist before people strikes me as lunacy.

 

[Meselwulf]

I see no reason to think that time has not always been as fundamental as distance in regards to the universe.



What are you talking about? We have no reason to quantize time yet.



Irrelevant. We are not talking about time as a we perceive it, we are talking about time as a physical dimension.



No, our universe is not timeless. A ticking clock immediately invalidates your statement. The equations of relativity do not tell us that the universe is timeless. If you wish to claim otherwise please provide a mathematical example in support of your position.

Have you ever heard of timelessness in GR?

It comes from quantizing Einsteins field equations. I guess you haven't then. The rest of your questions are irrelevant until you realize there are actually solutions to GR which have been quantized.

 

[Meselwulf]

No, nor do I care. Your apparent assertion that time did not exist before people strikes me as lunacy.

What strikes me as lunacy... sir... is you are not willing to hear the evidence at hand. You just want to throw it out so you don't need to hear it!

 

[Drakkith]

Energy and temperatures are related... what about the background TEMPERATURES OF SPACE?

This is made up of quantized photon energy.

The interaction is quantized through photons. The temperature itself is not quantized.

The BASIC temperature of a system vibrates at

$$1/2 \hbar \omega$$

And how does that support your claim that temperature is quantized?

 

[Meselwulf]

The interaction is quantized through photons. The temperature itself is not quantized.



And how does that support your claim that temperature is quantized?

The background temperature was given this name for a reason. You want to talk about background temperatures, then you must understand this is the least minimal action of energy a system can take AND IS A TEMPERATURE.

 

[Drakkith]

The background temperature was given this name for a reason. You want to talk about background temperatures, then you must understand this is the least minimal action of energy a system can take AND IS A TEMPERATURE.

That's nice, but I don't see how this answers or explains anything. It might help if you actually attempted to explain yourself a bit more.

 

[Meselwulf]

That's nice, but I don't see how this answers or explains anything. It might help if you actually attempted to explain yourself a bit more.

The background temperature can take a minimal value of 1/2 hbar omega. All systems can take this lowest energy at the quantized level, it is known as zero point energy.

 

[Drakkith]

The background temperature can take a minimal value of 1/2 hbar omega. All systems can take this lowest energy at the quantized level, it is known as zero point energy.

Let's say I have an object in thermal equilibrium with the background. The object emits a photon and loses that energy. Is it not in a lower energy state before it absorbs one from the background?