What is time??

[Dywyddyr]

There is a real example of space dilation

Except that this not dilation as it is understood in relativity.

that our universe is expanding . Is there also a real example of time dilation ? Is the duration of our day ( 24 hrs. ) increasing ?

See above. But actually the day is getting longer.
http://www.slate.com/id/2133359/

 

[BallisticBrian]

Except that this not dilation as it is understood in relativity.


See above. But actually the day is getting longer.

That quote is to do with the rotation of the earth slowing down, nothing to do with time dilation.

 

[Dywyddyr]

That quote is to do with the rotation of the earth slowing down, nothing to do with time dilation.

I know.
Read what I wrote regarding his comment on the universe expanding, and my reference to that comment before stating that the Earth is slowing down.
He's conflating two separate phenomena.

 

[Saquist]

No.
Space doesn't affect a clock. Time does.

That's not actually an absolute.

Time-dilation happens with acceleration
Time-dilation happens with the curvature of space time.

It wouldn't be unreasonable to make his statement.

 

[Dywyddyr]

That's not actually an absolute.

Time-dilation happens with acceleration
Time-dilation happens with the curvature of space time.

It wouldn't be unreasonable to make his statement.

And which part of that dilation is that affects the clock?
If it were simply "space dilation" then the clock would not slow down.
Hence the "time" part is required for the clock to be affected.

 

[scifes]

time is the secession of changes on something, if something doesn't change at all, then no time is passing with regard to it.

 

[RJBeery]

time is the secession of changes on something, if something doesn't change at all, then no time is passing with regard to it.

I agree with this. To most people "stopped time" is synonymous with a frozen world in which no change happens.

 

[Captain Kremmen]

Time is still passing even when nothing seems to be happening.
Some things take a long time.
Take Proton decay, which happens so seldom that no-one has observed it.


Despite the lack of observational evidence for proton decay, some grand unification theories, such as the Georgi–Glashow model, require it. According to some such theories, the proton has a half-life of about 10 to the power of 36 years, and decays into a positron and a neutral pion that itself immediately decays into 2 gamma ray photons:

Wiki


proton mass = 1.67262158 × (10 to the power of 27) kilograms

Doing a quick sum, 36 minus 27 is 9.
So if you had a mass of 10 to the power of 9 kilograms of just protons, and were watching them all carefully for a year, 1.67 of them would have a 50/50 chance of decay.
If they decay at all that is.

 

[RJBeery]

Time is still passing even when nothing seems to be happening.
Some things take a long time.
Take Proton decay, which happens so seldom that no-one has observed it.

This presumes that there is neither internal motion nor an external stimulus that initiates the decay. Even a typical explanation like vacuum flux leading to quantum tunneling is still obvious change in the environment. Stop the external interference and the internal motion and you have effectively "stopped time".

 

[Captain Kremmen]

This presumes that there is neither internal motion nor an external stimulus that initiates the decay.

Yes, I would assume that.
Is there a theory that decay is initiated by internal motion or an external stimulus? I thought decay was just a matter of probability.
Temperature, for example, doesn't have any effect on it.

 

[RJBeery]

Is there a theory that decay is initiated by internal motion or an external stimulus? I thought decay was just a matter of probability.
Temperature, for example, doesn't have any effect on it.

Decay isn't fully understood. For example

The emission is spontaneous, in that the atom decays without any interaction with another particle from outside the atom

but then later

The neutrons and protons that constitute nuclei, as well as other particles that approach close enough to them, are governed by several interactions. The strong nuclear force, not observed at the familiar macroscopic scale, is the most powerful force over subatomic distances. The electrostatic force is almost always significant, and in the case of beta decay, the weak nuclear force is also involved.

The interplay of these forces produces a number of different phenomena in which energy may be released by rearrangement of particles in the nucleus or the change of one particle into others. The rearrangement is hindered energetically, so that it does not occur immediately. Random quantum vacuum fluctuations are theorized to promote relaxation to a lower energy state (the "decay") in a phenomenon known as quantum tunnelling.

So wiki is saying that it's "spontaneous", but then explains that it's the particular interplay of internal forces, determined presumably by internal motion and/or quantum flux that causes decay to occur. It appears that spontaneity here means purely internal, rather than inexplicable, because they have gone on to suggest an explanation. Regardless, consider the following link:
"The strange case of solar flares and radioactive elements" which suggests that decay DOES rely, to some degree, on externalities.

In the end, all of the above suggests that without motion or some sort, decay would not occur (or at least, that's what I glean from it, your mileage may vary )

 

[arfa brane]

Despite the lack of observational evidence for proton decay, some grand unification theories, such as the Georgi–Glashow model, require it. According to some such theories, the proton has a half-life of about 10 to the power of 36 years, and decays into a positron and a neutral pion that itself immediately decays into 2 gamma ray photons:

The GG unified theory has been abandoned because no evidence for the decay of protons "spontaneously" has been found by the experiments.

Actually, this idea of spontaneous decay and uncertainty is kind of the opposite of our heuristic view of time--we prefer to use regular periodic motion (or 'functions' of motion) rather than spontaneous random events; although we do use radioactive decay rates to "time" the history of rocks, fossils, etc. because they all decay exponentially.

Once we have an 'algorithm' time is just a series of steps. For instance the day to night transitions of the Greenwich meridian is "synchronised" against another natural period which is the earth's orbital one. We also today use distant pulsars and other radio sources as a "universal" timebase. This is accurate enough to not only correct for the extra rotation (of less than a whole day) per year, but also determine rates of continental drift of the radio observatories relative to each other.

So we have a more universal (or at least a more universally distributed) sense of time these days.
If it's true that we can only have this "sense" of time if we have a clock, then what qualifies as a clock?
The earth's orbit and rotation qualify, so do distant pulsars, and so does radioactive decay although the last is more an "interval timer" or a stopwatch. Atomic transitions qualify as long as they are "regular" rather than random, which requires a certain amount of energy input, which is like a kind of "mechanisation" of the transitions, or a transformation into the Newtonian frame (which is where we prefer clocks to "live").

 

[Saquist]

And which part of that dilation is that affects the clock?
If it were simply "space dilation" then the clock would not slow down.
Hence the "time" part is required for the clock to be affected.

It's a matter of relativity.
A clock on Everest runs faster than a clock at the bottom of the Marianas trench. The only difference between them is the spatial location, yet the Everest clock appears to have accelerated forward in time.

 

[Dywyddyr]

It's a matter of relativity.
A clock on Everest runs faster than a clock at the bottom of the Marianas trench. The only difference between them is the spatial location,

I suggest you check the facts.
The reason for the difference in running speed is not the "difference in spatial location" - it's the strength of the gravity (i.e. the acceleration it is subject to) in which each clock is located.
If your contention were true why is there no difference in reading between a clock at the top of Everest and another at the same altitude but displaced (Top of Everest-bottom of Marianas) miles sideways?

 

[Eagle9]

What do the scientists think about this-can the time flow backwards? According to Special and General Relativity the time is delayed during fast motion and near very massive celestial objects, but time’s flowing direction does not change in such cases-it flows from past to future. But what about “reversing” this direction? Have there been run some experiments showing that this is possible? What do these two theories of Relativities say about this problem? Nothing?

 

[hansda]

No.
Space doesn't affect a clock. Time does.

Even for a pendulum clock, the time changes at different seasons for a same space location of the clock. The length (space) of a pendulum changes due temperature variation. Does it mean time dialation at different seasons.

 

[Dywyddyr]

Even for a pendulum clock, the time changes at different seasons for a same space location of the clock. The length (space) of a pendulum changes due temperature variation. Does it mean time dialation at different seasons.

Er, no. Since a pendulum clock is a mechanical system and a mechanical system has mechanical errors and variations.
Oh wait, are you going to suggest that a battery-powered clock with a flat battery indicates that time has stopped in its location?

 

[Captain Kremmen]

So wiki is saying that it's "spontaneous", but then explains that it's the particular interplay of internal forces, determined presumably by internal motion and/or quantum flux that causes decay to occur.

It still seems to me that if some kind of motion was required, then the decay would be dependent on temperature. Or at least stop at zero degrees.

Couldn't it just be that a particle has a statistical potential to change from one state to another, and given enough time it will do so?
I can see a problem with that too.

 

[Captain Kremmen]

Er, no. Since a pendulum clock is a mechanical system and a mechanical system has mechanical errors and variations.
Oh wait, are you going to suggest that a battery-powered clock with a flat battery indicates that time has stopped in its location?

I think that hansda is confusing the measurement of time with time itself.
He is talking about days, pendulums etc.

On the other hand, he might be trying to say something more subtle and interesting.

As a clock approaches the speed of light, from our point of view it will contract.

On the earth, if you made a second clock exactly the same as the clock which you originally sent speeding through space, but smaller, say the same size as the space clock now appears to be, it would show the wrong time. It would be going too fast.

Would this smaller clock show the same time as the space clock does?

 

[RJBeery]

It still seems to me that if some kind of motion was required, then the decay would be dependent on temperature. Or at least stop at zero degrees.

Couldn't it just be that a particle has a statistical potential to change from one state to another, and given enough time it will do so?
I can see a problem with that too.

I agree that if decay rate had to do with internal motion it seems that slowing that internal motion would slow the decay rate. On the other hand, if decay rate was dependent upon quantum flux that occurred within the locale of the atom it could be considered "internal behavior" that may be impervious to temperature.

Lastly, I'm maintain that if we're able to influence the decay rate in any way, either by proximity to the sun or by simply staring at the material, then the process is clearly not simply an intrinsic/internal "statistical potential".
From another article...

Jenkins and Fischbach suggest that the changes in the decay rates are due to interactions with solar neutrinos, nearly weightless particles created by nuclear reactions within the sun's core that travel almost at the speed of light.

It is estimated that about 60 billion solar neutrinos pass through a person's fingernail every second, but they are so weakly reactive that they pass right through the body without disturbing or changing anything, Jenkins said.

"We haven't known the solar neutrino to interact significantly with anything, but it fits with the evidence we've gathered as the likely source of these fluctuations," he said. "So, what we're suggesting is that something that can't interact with anything is changing something that can't be changed."

The Purdue team has ruled out the possibility of experimental error or an environmental influence on the detection systems that track the rate of decay as being responsible for the fluctuations and published a series of papers in the journals Astroparticle Physics, Nuclear Instruments and Methods in Physics Research, and Space Science Reviews.

Sturrock said it is an effect that no one yet understands and that if it is not neutrinos that are responsible, then perhaps there is an unknown particle interacting with the atoms.

"It would have to be something we don't know about - an unknown particle that is also emitted by the sun and has this effect - and that would be even more remarkable," he said.

"So, what we're suggesting is that something that can't interact with anything is changing something that can't be changed." Gotta love it.