i was pondering this for a couple of hours now randomly searching the web. Do you think that a constant time is a convenience to us - however it isn't constant in the grand scheme of things?

Time is not constant. Only the speed of light is constant in a vaccumm. The acceleration in this case is the acceleration in our frame of reference. If we changed frames we would change the rate of acceleration that we observe.

Another point here is that the time isn't changing, but the distance is actualy changing. That is space is expanding causing the acceleration.

Someone explain to me how light can travel in anything other then a vacuum when it is soooo small that it travels between the elementary particles where everything is vacuum.

When light travels through water it is still traveling at full speed it just takes longer to get from one end to the other because it does not take a direct route as it is bouncing all over the place.

Expansion is a process, which means it happens over time. So it makes no sense to talk about the expansion of time, or spacetime. What we mean when we say space is expanding is that the shape of spacetime is such that as you move in a timelike direction, distances between inertial observers in a spacelike direction get larger.

You can visualize this as something like a sphere: as you move north or south the lines of longitude get closer or further apart. If you think of time as the north/south direction, so that space is a 1D circle, then people in this spacetime would observe the universe expand, reach a maximum radius, and then contract.

In de Sitter's universe, time and space are modeled as a sphere - expasion of the sphere dilates both time and space. In Einstein's universe, time and space are modeled as cylindrical

I happend to come across these forums when I was searching just on this subject matter.
I am not a PHD, or a Doctor, or even have a degree in Physics, my interest is merely entertainment as I happen to learn that I am quite good at conceptual Physics theory.

To address Craig's response:

You say Time is not constant, yet time is measured based on the speed of light reaching the earth as a point of reference. That being said, it leads me to my next question just to kind of stir up imagination and start a discussion about it.

If time is not constant, do you believe time travel to the past is possible?

On this note, expansion of the universe technically would not dilate time, if time is constant. It is my belief time is constant, which in this case means there is no relevance how the universe is model'd or who was correct or not. If time is constant it can not be dilated.

My particular intrest is in Conceptual Relativity Theory. Just something I like to investigate from time to time out of sheer interest.

I personally believe time is constant. Mathematically I can't prove it, but, logically I can... If you care to discuss it further in detail.

I would say:
1) time is constant in each observers inertia frame
2) time and place are not orthogonal in any inertia frame except your own

Backward time travel no.
Forward time travel yes - just move fast then wait awhile then stop moving - of course it all depends on which frame you are thinking in terms of

Top bold is exactly why I believe time is constant. But to expand on that idea... If traveling back is not possible, then how is traveling forward based on #1?

Think of it in terms of solving a linear one step algebra equation: Where A = B

If A = the past and B = the future the = sign is the present.

What you are saying is: I can not change A, but I can change B. What would happen if you do?

Basic principle states: What you do to 1 side of the equation you have to do to the other.

A = B

i.e. 3x + 1 = 4 If we solve for X we have to manipulate A and B equally. If we do not balance out time and space, they will annihilate eachother. To the point = (present day) and the past (A) no longer exsist. This is also the basic idea behind paradox theory. Ever watch the movie Back to the Future? It is filled with Paradoxial situations that never get resolved or to relate it to this discussion (The equation isn't balanced). I find that movie entertaining to watch from this standpoint.

I believe you can not time travel to the past, or the future, because time is constant and time is relevant in all orthogonal inertia frames or all non orthogonal inertia frames. So on this point I agree. But, time and space can be orthogonal and the principal remains the same.

Sorry, to clarify more about the linear equation analogy:

100 years in the past someone invents a time machine and comes to our present day to talk to you and me. This results in the annihilation of the present and futures. We would not be talking about this right now.

Someone today builds a time machine and talks to the person who invented it 100 years ago. The present day as we knew it and the future have just been destroyed. We would not be talking about this right now.

Where as someone 100 years into the future invents a time machine and comes back to the present day to talk to you and me. He has just destroyed the present and future. Our present day no longer exists as we have made a tangent in space time the moment this person arrives. He destroys his past: which you and I are talking about right now. But he also destroys our future since he never left to our present day yet.

This is due to the balance that must be maintained. I believe if the balance between time and space are not maintained it would destroy the universe. Quite literally, the universe as I perceive it would blink out of existence.

If 100 years ago someone got in their spaceship and accelerated to a [tex] \gamma [/tex] of 100. In that state they wait one year on their local clock and then decelerate arriving here and now to talk with you and me. No problem. All is fine.

We accelerate an object that object would cease to exsist in the present, because it went into the future?

The concept of absolute space emphasizes dissimilarity between acceleration and deceleration. On absolute space, acceleration and deceleration are completely opposite actions for any relative observer. Hence, opposite effects of acceleration and deceleration on matter (relative mass increase or decrease) is concrete for any relative observers.

This point has been ignored in special relativity, which cause the twins paradox.

That being said, I leave you with this word problem:

Points A, B, C and D. Distance between Point A - B is equal to the distance between Point A and C. The distance from point A and D is equal to the distance between AB or AC respectively. Person 1, 2, and 3 are all the exact same age.

Person 1 travels at 1/2 speed of light from Point A to B and it takes him 10 years to make the journey. Person 2 travels at the speed of light from Point A to C and it takes him 5 years to make the journey. Person 3 travels at 1.5 x Speed of Light, from Point A to Point D and it takes him 2.5 years to make the journey. If Person 2 waits 5 years before leaving from the time Person 1 leaves and Person 3 waits 7.5 years before leaving at the time Person 1 leaves:

Who arrives at their destination first?
Which person is older?
Which person time travels?

Time is just a concept. It has no physical reality. There is only the present. No past or future. These are just concepts also. The universe as a whole changes state over time and it is this rate of change that is construed as time. Is this rate of change constant over the universe ? I doubt it. It is likely that as an object speeds up its rate of change (and therefore its experience of time) slows down.

We have to be careful with the phrase "its experience of time". If you mean they do not age as much as we in the still frame do then yes. If you mean they in their frame see themselves as moving slowly no. If you mean they in their frame see us in the original frame as moving slowly no.

I believe, time is constant, and only moves in a linear direction at the same rate from any relative perspective. Take my word problem as an example:

Points A, B, C and D. Distance between Point A - B is equal to the distance between Point A and C. The distance from point A and D is equal to the distance between AB or AC respectively. Person 1, 2, and 3 are all the exact same age.

Person 1 travels at 1/2 speed of light from Point A to B and it takes him 10 years to make the journey. Person 2 travels at the speed of light from Point A to C and it takes him 5 years to make the journey. Person 3 travels at 1.5 x Speed of Light, from Point A to Point D and it takes him 2.5 years to make the journey. If Person 2 waits 5 years before leaving from the time Person 1 leaves and Person 3 waits 7.5 years before leaving at the time Person 1 leaves:

Who arrives at their destination first?
Which person is older?
Which person time travels?

The answer to the questions:

They arrive at the same time.
Neither person is older. They remain the same age.
Neither person travels in time forwards or backwards.

What makes the bold statement true given my example for why it's not true?

In SR, your example simply can't happen, because a spaceship can't travel faster than light.

But of course in SR it's very possible to travel forward in time. In fact it's been measured in various experiments to considerable accuracy.

Do you think physicists just decided they liked the idea that time wasn't constant? No, they hated the idea, but it was forced on them against their will by reality. It's no exaggeration to say the scientific community was shocked and bewildered by the unrelenting observations and experimental results showing that time wasn't the constant they had all religiously assumed it was.

It seems to me that there are only three choices to deal with this:

1. Find contrary empirical evidence.
2. Show an internal logical flaw in SR.
3. Accept that time is not a constant.

Many physicists and others have tried 1 and 2 repeatedly over the last hundred years, and all their efforts only reinforced 3.

That being said, attempts at 1 and 2 are still valuable to science, and the first step in either of them is to thoroughly understand SR.

You and I stand in front of eachother. I say to you, "Time is constant." You say to me, "Time is not constant."

To prove our points... You walk in a circle the diameter of 36 inches at the speed of light for 1 minute and then stop to compare the time on our watches.

Now, From my perspective you disappeared for 1 minute. From your perspective I just stood there motionless for 1 minute. You stop moving and we compare the times on our watches.

Your watch is 1 minute ahead of mine.

Which of us is older?

Taking into account all perspectives. You disappeared for 1 minute. But from your perspective I was motionless for 1 minute. We age at the same rate relative to time being constant.

The ONLY way to prove the answer is to violate the Pauli Exclusion Principle. Which loosely translated means, "No 2 piece of matter can occupy the same intertial frame at the same time" else there is no possible way to derive a conclusion that time is not constant. It was confirmed testing Fermion particles in a simultaneous quantum state, and proven not possible. You or I would have to exsist in both interial frames at the same time in order to confirm that time is not constant, or that it is constant, and this is just not possible.

Did time not travel in a linear direction? That direction being: Forward, and at a constant rate to all relative perspectives?

Does that make you 1 minute younger than me?

Point is, time travels at a constant rate "Foward" it can not be stopped, reversed, or accelerated in any linear direction when all relative perspectives are taken into account.

Because they tried to create a reality that they had no means to create. Just like my example: I have no means to create the experiment, but why should that stop anyone from believing the world was round before they could prove it?

So what you are saying here is: Einstein's Theory of Relativity is wrong?

He stated, "When traveling close to the speed of light time slows down, when traveling at the speed of light, time stops, and when traveling faster than the speed of light time travels in reverse."

Well if it's not possible to travel faster than the speed of light, how can one assume time goes in reverse at any point what-so-ever relative to the speed of light?

Question: Why do we have to accelerate matter to time travel? If time travel is possible and people believe it's possible, why do we have to accelerate matter to, at, and beyond the speed of light to accomplish time travel?