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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 04/01/2019 16:23:02 »

PS: I think the best definition of time I have ever heard is this (roughly):

"Time is what keeps everything from happening at once"

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 04/01/2019 16:22:10 »

Doesn’t the second law of thermodynamics state that in a closed system, entropy tends to increase, or to remain constant.  In spite of the presence of the word “tends”, the assertion “it never decreases” can still be found attached to many explanations.  Could this be a source of confused thinking?  Even in a closed system, can “time progress” in the direction of decreasing entropy?

My understanding is that entropy does not, in fact, determine the arrow of time--it merely demonstrates that there is an arrow.
Entropy is just a natural outcome of statistics. The fact that it is increasing only means that the universe started in a highly ordered state, and is still much more ordered than it ultimately will (can) be.

If we have a small closed system entropy can increase or decrease depending on the initial state.

Imagine four coins that can be either H or T. At regular intervals a coin is selected at random, and flipped such that it has a 50/50 chance of being H or T.

If the system starts out HHHH (the lowest possible entropy for the system), then after the first flip, entropy has a 50% chance of increasing and 50% chance of staying the same. Eventually the system will reach a state of maximal entropy, and can then only decrease or stay the same. Ultimately, as this game continues, the system will oscillate through all possible states with all levels of entropy (with each of the states essentially being favored by entropy).

This scenario is also only valid if the coins are all equivalent, and we don't care about their relationships to each other (you can think of this as the difference between combinations and permutations). If every coin is unique, then all states are equally likely, and have identical entropy. Entropy of the system will never change even though the system clearly changes as the coins are flipped.

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 04/01/2019 12:30:47 »

I like a good debate but the concept of time seems to be flogged to death for no reason.

“Flogged to death” – Yes.    “For no reason” - No.

I think the reason that the subject of time, in a variety of guises, keeps appearing is twofold.

1. We tend to be with St. Augustine, when he said: “What then is time? If no one asks me, I know;
if I wish to explain it to someone who asks, I know not.”

2. We easily lose sight of the point that you make:

It is simply a mechanical means of measurement of change in one form or another.

   
A major factor is the way in which we talk and think about time.  For example: we talk of time passing, when what we probably mean is something along the lines of: change occurs continually, and therefore, we see a progression in time, which is what we use to measure that change.

I doubt that even the most inveterate pedant would suggest that the protracted version would be preferable.  As long as our thinking is adjusted appropriately, the “shorthand” version is fine.  Taking “analogies” too literally, though, tends to lead to confused thinking.

Some examples from this thread include:

  "Change" tells you that time exists.

Change tells us that change exists.  We add the concept of time.

But "change", by itself, doesn't explain the other major characteristic of time: That it seems to travel in only one direction.

The idea that time travels is, in itself, an analogy that should not be taken too literally.

For this you have to look at entropy: Time flows in the direction where entropy increases.

Doesn’t the second law of thermodynamics state that in a closed system, entropy tends to increase, or to remain constant.  In spite of the presence of the word “tends”, the assertion “it never decreases” can still be found attached to many explanations.  Could this be a source of confused thinking?  Even in a closed system, can “time progress” in the direction of decreasing entropy?

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 04/01/2019 08:10:00 »

I think it is very difficult to distinguish between our own personal perceptions of time (which is subjective and based on many complicated and poorly understood biophysical and psychological mechanisms) from the the fundamental temporal dimension that our mathematical models use. Additionally, it is important to remember that even the versions of "time" invoked in our various models is not an accurate representation of whatever "time" "actually" "is"

As far as time standing still in the quantum world... don't be confused by the fact that quantum objects don't appear to follow the same rules as macroscopic objects. The rules are the same (the real world and the quantum world are the same world), we just have to remember that macroscopic objects are collections of vast numbers of elementary particles whose properties are very strongly correlated with each other. This necessarily means that the most important processes and interactions of these enormous collections will be quite different from very small collections of particles.

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 04/01/2019 03:14:33 »

If anyone has used a stopwatch they are aware of time as a measurement of change.

I can only speak for myself  but I  personally seem to feel a need to "anthroposize" time or more accurately to give it its own elemental existence (the Greeks certainly did this with their Chronos).

Naturally I assume that the "general population" shares my (outdated) instincts  and so might only  appreciate that a stopwatch only measured change if it was first suggested to them.

Perhaps ,even then they might only agree to that  in a lip-service kind of way and hold onto the notion that indeed "time is passing" as if it was a "thing" ...or maybe they would cop on more quickly than myself whom I admit to be a snail like learner at best.

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 04/01/2019 02:15:11 »

Depends Harri.

First of all, there is no way for an observer macroscopically to be without his local clock . So even if quantum objects would be 'time less', we have no way I know of to prove it. Our clocks always tick.

The other thing is a question of what 'time' is. Is it a 'creation' of SpaceTime, similar to decoherence, scale dependent? Or a 'property' of SpaceTime, both microscopically and macroscopically.

We will always find a past, a 'present' and a future, until we're dead.

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 03/01/2019 22:42:58 »

If anyone has used a stopwatch they are aware of time as a measurement of change.

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 03/01/2019 22:00:00 »

I like a good debate but the concept of time seems to be flogged to death for no reason. It is simply a mechanical means of measurement of change in one form or another. The fact that those mechanics don't always run at the same pace in different frames is not that difficult.

Yes,a fair point.

On the other hand "time" has always (I imagine) been a focal point of humanity's  thoughts....until ,amazingly we are introduced to time dilation and  the non existence of absolute time.

Small wonder we are ,on an individual basis trying to keep up with the new normal  some 100 years later.

And how many of the general public are even dimly aware what special and general relativity have meant for our understanding of what can be called the "timing as a measure of change" mechanism?

Would they care ? Would they "believe"?

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 03/01/2019 21:34:16 »

I like a good debate but the concept of time seems to be flogged to death for no reason. It is simply a mechanical means of measurement of change in one form or another. The fact that those mechanics don't always run at the same pace in different frames is not that difficult.

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 02/01/2019 11:41:04 »

I have had ,in the past  the belief that time required motion  to exist.However I have been assured that   clocks that rely on radioactive decay show that this is not the case.(no motion)

I had responded to the posted question, but not so much to the thread title.  This is an interesting point.

Given a universe with but one unstable particle, it will decay at some point, and it would be indistinguishable if it took a year or a microsecond to do that.  Time would be meaningless.  But given two different particles, suddenly one has a measurably greater probability of decaying than the other.  Time is still sort of meaningless, but that very real probability of decay makes it not totally meaningless.  That's just two particles, and already we can see 'classic' time emerging.

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 02/01/2019 09:19:05 »

Past, present and future = change?

"Change" tells you that time exists.

But "change", by itself, doesn't explain the other major characteristic of time: That it seems to travel in only one direction.

For this you have to look at entropy: Time flows in the direction where entropy increases.
- You can't tell the direction of time by looking at a single particle
- You often can't tell the direction of time by looking at the interaction of 2 particles
- But by the time you look at the interaction of 3 or more (real) particles, the direction of time is usually apparent

See: https://en.wikipedia.org/wiki/Entropy_(arrow_of_time)

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 02/01/2019 00:15:02 »

in quantum, spin is angular momentum, but quantum spin is unlike angular momentum spin in a hadron vector quantity. spin for a hadron is unidirectional and relates to time in a linear frame.. quantum spin is multidirectional. This mean that it's spin carries no vector orbital properties. as such, it cannot be used to measue linear time.

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 01/01/2019 23:47:15 »

I have had ,in the past  the belief that time required motion  to exist.However I have been assured that   clocks that rely on radioactive decay show that this is not the case.(no motion)

I also wonder (from bits and pieces I have heard)  whether it may be the case in the quantum world  that all particles are indistinguishable from each other..would that rule out   "change" at that level?

So ,how would one go from  the universal sameness of the quantum realm (if that is indeed how it is  or might be) to the variety of the classical realm?

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 01/01/2019 23:46:53 »

On a large scale, the world we exist in and the universe our world exists in has been, and as far as I am aware is forever changing. Using a second as a measurement for instance, our universe has been changing every second since the big bang, it is changing every second as I sit here typing this, and will continue to change every second into the future. Would this be a legitimate way of describing what is meant by a past, present and future? Past, present and future = change? If so, would the same be said of the quantum world?

Time is change.  Without change, there would be no meaning to time.
Past, present, and future are local relations to a specific moment: If 3 events are ordered A, B, and C, then B is in the past of C and in the future of A, and each event occurs in the present of itself.
This is no different than floors of a building, where floor 12 is below floor 18, but above floor 7, and all three floors are 'here' in reference to themselves.

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Physics, Astronomy & Cosmology / Re: Is there a detectable direction in which the universe is expanding?

« on: 20/12/2018 22:13:13 »

If the universe was 'flat' then I assumed that there must be an observational spatial direction in order to determine it was flat.

Flat means that parallel lines stay the same distance apart, in any direction.  Yes, direction matters, but our space seems symmetrical this way.  With positive curvature (like the balloon), parallel lines meet.  With negative curvature (like kale), parallel lines diverge.

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Physics, Astronomy & Cosmology / Re: Is there a detectable direction in which the universe is expanding?

« on: 20/12/2018 14:48:47 »

Is there a detectable direction in which the universe is expanding?

Outwards. 

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Physics, Astronomy & Cosmology / Re: Is there a detectable direction in which the universe is expanding?

« on: 20/12/2018 10:42:52 »

The Solar System (and our local galaxy cluster) seems to have a measurable motion with respect to the Cosmic Background Radiation. The CMBR seems to be slightly red-shifted in one direction, and slightly blue-shifted in the opposite direction.

Whether this represents random motion of our galaxy, a local gravitational concentration or a random temperature variation in the CMBR is not known for certain.

See: https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy

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Physics, Astronomy & Cosmology / Re: Is there a detectable direction in which the universe is expanding?

« on: 19/12/2018 22:56:48 »

If the universe is flat then is it possible to detect a direction in which the expansion is travelling? Perhaps taking the earth/solar system as a point of reference.

From any spatial point of reference, like here, the universe spatially expands equally in every direction.

From an objective viewpoint, I suppose the balloon analogy is appropriate.  Earth is a dot on the balloon, and all the other stuff is other dots drawn elsewhere.  As the balloon expands equally, every dot moves away from a given reference dot in proportion to its distance from that reference dot.  This is exactly as we observe things.

So is there a direction to the balloon expansion?  Yes, but it is outward, not in any spatial direction that you can point with an arrow on the balloon surface.  In the same way, there is no arrow you can make showing the expansion direction.  The direction is outward in that 4th direction that you can't point with a spatial arrow.

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Physics, Astronomy & Cosmology / Re: Is there a detectable direction in which the universe is expanding?

« on: 19/12/2018 22:12:12 »

It's expanding in all directions at once.

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Physics, Astronomy & Cosmology / Re: If the Universe expanded more slowly, what would happen to light?

« on: 19/12/2018 00:24:58 »

As the title says, if the universe were to slow down and perhaps even reverse direction, what would happen to light that was and is now travelling towards the edge of the universe?

As I understand it, the universe is expanding faster than the speed of light.

The expansion of the universe isn't a speed that is measured in distance per second.  It doubles its dimensions every 2x amount of time.  You can't technically double that.
Anyway, if the expansion rate were half since the beginning, it would today have the visible dimensions it does now: at age 13.8 billion years, the stuff 13.8 billion light years away will be going away at light speed, just like it is now (sort of, this is assuming the rate is constant, which it isn't).

But there would be twice as much matter between here and 13.8 billion light years away.
Maybe.  Matter is energy, and half the expansion rate is half the energy, so half the matter would be generated, so it perhaps would look just like it does now.  It all depends on what you decide to hold constant while messing with the expansion rate.