Question Relativity and the past and future

[iNow]

The space twin is in his year 2000. He starts to drift in outer space. The earth twin is in his year 2050. He takes off in a sister ship and docks with the space twins ship in outer space. The twins meet in an air lock between the ships. Does the earth twin fall back to the year 2000, or does the space twin jump to the year 2050?

,

 

No, they are both in the present, but their calendars say different things.

 

Think about the time difference between the United States and Australia. It may be Monday in Australia while it's still Sunday in the United States, but that does not mean that they travelled into the future or the past, it just means that their clocks are set differently.

 

The analogy doesn't fit completely, as the the twin who stays on earth actually has their calendar flip through the months and years more quickly than the twin in space, but when they meet, they are in the present. They just disagree on how long it took each of them to get there.

[Slinkey]

The space twin is in his year 2000. He starts to drift in outer space.

 

What is this twin "drifting" relative to? If you mean he has switched his engine off that does not mean he is not moving. This statement on its own is incomplete.

 

The earth twin is in his year 2050. He takes off in a sister ship and docks with the space twins ship in outer space.

 

Why are the two twins recording different years? How did that happen?

 

The twins meet in an air lock between the ships. Does the earth twin fall back to the year 2000, or does the space twin jump to the year 2050?,

 

You haven't told us how far the twin had to travel nor at what velocity thus your question is unanswerable in its current form.

 

What is certain is that neither twin will record the year "2000" (we need a more specific time co-ordinate as a year is an awfully large time "slice") when they meet up but it is entirely possible that when they meet they will think it is the same year as each other depending on how far the traveling twin had to travel and how fast he traveled there. It would be quite possible for them to both record the year "2052" for example depending on velocity and distance.

[asprung]

It seems that when the twins meet there must be one date of their meeting. What is it? In the year 2000, or the year 2050? The space twin had not yet arrive at the year 2050,while the earth twin had long passed the year 2000.

[iNow]

It seems that when the twins meet there must be one date of their meeting.

There isn't. There's no such thing as absolute time. The difficulty you are having accepting this seems to be at the heart of your confusion. There is no absolute time.

[Slinkey]

It seems that when the twins meet there must be one date of their meeting.

 

They can meet in the same frame of reference but as dates are arbitrary conventions there is no neccesity for them to agree what the date is. Any point in spacetime does not have an absolute date, and I think this is where you are having the real difficulty grasping what you have previously been told in varying ways.

 

What is it? In the year 2000, or the year 2050?

 

As I said in my previous post - without the information I asked for it is incalculable. In order for any kind of precise answer you need to furnish us with how far apart they were at the start of the journey and the velocity of the moving twin. This information is crucial if you want an answer.

 

Do not take offence but your simplistic questions expose how little you really understand about this subject. In order for you to progress you have to put aside the idea of absolute, or Newtonian, time for a start. It simply does not exist in reality. There is no universal clock like you see in Star Trek.

 

Then you need to understand that movement is a relative concept. Imagine an empty universe with only yourself in it. How would you be able to tell if you are moving or not? In an empty universe you would have no reference points to tell you if you are moving, and even if you did have reference points you would not be able to tell if you or the reference points, or both, are moving.

[swansont]

As I said in my previous post - without the information I asked for it is incalculable. In order for any kind of precise answer you need to furnish us with how far apart they were at the start of the journey and the velocity of the moving twin. This information is crucial if you want an answer.

 

No, the answer is incalculable, period. As has been repeatedly pointed out, the framing of the question implies the existence of absolute time, and that is the fatal flaw in the problem.

[Slinkey]

No, the answer is incalculable, period. As has been repeatedly pointed out, the framing of the question implies the existence of absolute time, and that is the fatal flaw in the problem.

 

I beg to differ on that and I was not invoking absolute time either.

 

If in one frame the date is 2000 and the other 2050 and one travels a known distance at a known velocity then you can indeed work out the dates that both frames of reference will claim when they meet in the same reference frame.

[swansont]

I beg to differ on that and I was not invoking absolute time either.

 

If in one frame the date is 2000 and the other 2050 and one travels a known distance at a known velocity then you can indeed work out the dates that both frames of reference will claim when they meet in the same reference frame.

 

The question as framed by asprung only allows one answer.

[asprung]

As I see it, time is a succesion of the occurence of events. Once an event has occured it cannot be erased or altered. The space twin whose time has slowed compared to earths will not as yet have experenced certain events which have occured on earth. His future must thus be predetermined or he would have the ability to rewrite earths history.

[Klaynos]

But the events have happened to him, just at a different rate.

[asprung]

I only said it once but some how it downloaded 4 times. Whats in error?

 

How can an event that first occured in the year 2050 have occcured while the space traveler is still in the year 2000 irrespective of rate?

[losfomot]

I only said it once but some how it downloaded 4 times. Whats in error?

 

How can an event that first occured in the year 2050 have occcured while the space traveler is still in the year 2000 irrespective of rate?

 

The space traveller is not IN the year 2000. There is no such thing as a universal 'year 2000'.

 

If the space traveller leaves Earth in 1999, travels in space for a year, and comes back to Earth in the year 2050... Then the space traveller is on Earth in the year 2050, he is not in the year 2000.

 

The space traveller will NEVER experience the 'year 2000' because he was not in Earth's frame of reference that year. He will never experience 2001, 2002, 2003... or 2049, because he was not in Earth's frame of reference during those years, and he cannot go back in time to get them back... the past is past.

[swansont]

As I see it, time is a succesion of the occurence of events. Once an event has occured it cannot be erased or altered. The space twin whose time has slowed compared to earths will not as yet have experenced certain events which have occured on earth. His future must thus be predetermined or he would have the ability to rewrite earths history.

 

The time passes at different rates — it stretches, as it were — so there isn't a 1:1 mapping between the two frames. Again, you are using an absolute time.

 

An event occurs and both observers see it. But they will disagree on what time the event occurred. To one observer, the event happened at noon, but to the other it happened at 1 PM, because his clock has run faster.

[asprung]

Do you mean that all the events that occur for the earth twin up through the year 2050 are occuring for the space twin as if he was experencing the same now as the as the earth twin.

[swansont]

Do you mean that all the events that occur for the earth twin up through the year 2050 are occuring for the space twin as if he was experencing the same now as the as the earth twin.

 

I'm not sure how you mean "the same now."

 

But here's an example: the twin leaves in 2000 with their clocks synchronized — they both agree on this — and returns in what he says is 2010, but the earth twin thinks it's 2050.

 

The earth twin sets off fireworks on the twins' birthday each year, bright enough for the space twin to see. They each observe 50 firework events. The earth twin thinks they happened a year apart. The space twin does not, because his clock was not running at the same rate.

[phyti]

asprung;

 

I have been told that according to the theory of relativity if a man leaves Earth in a spaceship, and travels at a speed approaching I the speed of light his time passes slower than time on earth.

 

If this is so, when the man returns to earth his calendar date and his time would be behind earths; he would be in earths past, and earth would be in his future.

 

How could this be?

----

 

Forget 'time is passing', and think 'events are happening throughout the universe'.

The rate of activity for the traveler in his spacecan, his clock, and everything that moves with him is slower because of his motion. Why, because all interactions at the atomic, molecular, and biological level are mediated by em/light exchange, and the speed of light propagation in space/vacuum is constant.

When he reads the slow running clock, his slow running memory can't detect it. Similar to 'length contraction',...if his spacecan did shrink 50%, he couldn't tell with his measuring rod which is 50% shorter. It's a matter of scaling, the difference being the clock events (ticks) are fewer and farther apart.

If his clock intervals are longer, and he sees the same number of events happening in the outside world, then his clock intervals contain more events than those of his earth-twin.

The same number of events happen for both, the traveller just partitions his 'time' into bigger pieces. Both persons remain in the 'now' world because there is no where else to be!

[thedarkshade]

Now is eternal!

[asprung]

Great I am no longer confused. Thank you all very much.

asprung

[phyti]

Great, another satisfied customer!