Do We See A Train Arrive That Arrived 8 Minutes Earlier?

[xyz]

Standing on a platform waiting for a train to depart.  The train is a special train and can travel at the speed of light c. 

 

 

I know the train will take 8 minutes from departure to arrive at the next station, the train departs and arrives at 12:08 pm at the next station. 

 

However! we do not see it arriving at the next station until 12:16pm from the platform at the  departure station.  

 

At the next station awaits my friend for the return trip that departs at 12:10pm

 

However I see him arriving at the next station at 12:12pm 

 

 

Is my friend late or early for the train?

 

 

 

 

 

 

 

 

 

 

[CraigD]

From the information given, we have that “next station” and “departure station” are 8 light-minutes (143900379840 meters) apart. So if you, xyz, standing at “departure station”, see your friend arrive at the next station as your clock reads 12:12 PM (we assume everybody has an accurate clock synchronized to a common time), his clock, at “next station”, reads 8 minutes earlier, 12:04 PM. So your friend arrived 6 minutes early for the train departing “next station” at 12:10 PM.

 

Nothing in this question requires any use of relativity. Here’s one that does:

• Xyz’s friend gets on the train, which departs “next station” at 12:10 PM and, traveling instantly at the speed of light, arrives at “departure station” at 12:18 PM (according to xyz’s clock).
• Xyz and his friend meet 2 minutes later. Xyz’s clock reads 12:20 PM.
• What does his friend’s clock read?

PS: We could stand to have better names for the train stations than “departure” and “next” – how about “Shady Grove” and “Tartarus”?

PPS: This must be taking place on some huge, artificial world, something like a giant flat (so you don’t lose sight of the stations over a horizon) disk with a diameter as great as the distance from the Earth to the Sun. Xyz must have a fantastically good telescope to see details as small as the train and his friend at a distance of 8 light-minutes.

[A-wal]

Nothing in this question requires any use of relativity. Here’s one that does:

• Xyz’s friend gets on the train, which departs “next station” at 12:10 PM and, traveling instantly at the speed of light, arrives at “departure station” at 12:18 PM (according to xyz’s clock).
• Xyz and his friend meet 2 minutes later. Xyz’s clock reads 12:20 PM.
• What does his friend’s clock read?

12:12 and a bit. I know you meant to say a touch under the speed of light. :)

[xyz]

From the information given, we have that “next station” and “departure station” are 8 light-minutes (143900379840 meters) apart. So if you, xyz, standing at “departure station”, see your friend arrive at the next station as your clock reads 12:12 PM (we assume everybody has an accurate clock synchronized to a common time), his clock, at “next station”, reads 8 minutes earlier, 12:04 PM. So your friend arrived 6 minutes early for the train departing “next station” at 12:10 PM.

 

Nothing in this question requires any use of relativity. Here’s one that does:

• Xyz’s friend gets on the train, which departs “next station” at 12:10 PM and, traveling instantly at the speed of light, arrives at “departure station” at 12:18 PM (according to xyz’s clock).
• Xyz and his friend meet 2 minutes later. Xyz’s clock reads 12:20 PM.
• What does his friend’s clock read?

PS: We could stand to have better names for the train stations than “departure” and “next” – how about “Shady Grove” and “Tartarus”?

PPS: This must be taking place on some huge, artificial world, something like a giant flat (so you don’t lose sight of the stations over a horizon) disk with a diameter as great as the distance from the Earth to the Sun. Xyz must have a fantastically good telescope to see details as small as the train and his friend at a distance of 8 light-minutes.

 

Shady Grove and Tartarus sound good names for our stations, however we could just compare to the Earth and the Sun and the relatively ''flat'' observation of space. 

 

If I was at Shady grove and my friend was at Tautarus, both our clocks synchronised, my friends clock would show the same time as my clock on the arrival (ignoring the  ''time'' dilation). 

 

If I departed for Tartarus and you departed for Shady Grove , at 12am, we both arrive at 12.08am at our destinations. 

[A-wal]

If you're just going to ignore physical effects then the statement is meaningless. Their clocks wouldn't show the same time, the traveler's clock would be eight minutes behind the other's clock.

[xyz]

If you're just going to ignore physical effects then the statement is meaningless. Their clocks wouldn't show the same time, the traveler's clock would be eight minutes behind the other's clock.

How do you possibly come to that conclusion?

 

If you travelled at c to the Earth from the Sun and depart from the Sun at exactly 12pm, what time do you arrive at the Earth?

 

If I simultaneously,  left the Earth at c and travelled to the Sun at exactly 12pm, what time do I arrive at the Sun?

[A-wal]

"How do you possibly come to that conclusion?"

 

Because that's how it works.

 

 

"If you travelled at c to the Earth from the Sun and depart from the Sun at exactly 12pm, what time do you arrive at the Earth?"

 

12pm own your own watch, 12:08 on an Earth watch, 12:16 on a Sun watch (because of the eight minutes it would take for the light from Earth to reach the Sun).

 

 

"If I simultaneously,  left the Earth at c and travelled to the Sun at exactly 12pm, what time do I arrive at the Sun?"

 

Same thing. 12pm own your own watch, 12:08 on a Sun watch, 12:16 on an Earth watch (because of the eight minutes it would take for the light from Sun to reach the Earth).

[xyz]

"How do you possibly come to that conclusion?"

 

Because that's how it works.

 

 

"If you travelled at c to the Earth from the Sun and depart from the Sun at exactly 12pm, what time do you arrive at the Earth?"

 

12pm own your own watch, 12:08 on an Earth watch, 12:16 on a Sun watch (because of the eight minutes it would take for the light from Earth to reach the Sun).

 

 

"If I simultaneously,  left the Earth at c and travelled to the Sun at exactly 12pm, what time do I arrive at the Sun?"

 

Same thing. 12pm own your own watch, 12:08 on a Sun watch, 12:16 on an Earth watch (because of the eight minutes it would take for the light from Sun to reach the Earth).

Sorry I am confused, I do not understand where you are getting the extra 8 minutes from, the speed of c is constant and does not reduce to half the speed when ''i'' am travelling to the sun. 

 

 

What do you mean the 8 minutes it takes light to arrive from the Sun?  the light from the sun is continuous to the earth and not broken and already here. 

[A-wal]

Nothing's moving at half speed. It takes 8 minutes for the traveler to make the trip between the earth and sun and a further 8 minutes for the light to travel back to the staring point so the trip is completed in 8 minutes on a clock at the destination and 8 minutes after that on a clock at the starting point. It takes no time at all on the travelers clock because they're moving at the speed of light.

It's only "already here" after the 8 minutes it takes to travel from the sun to the earth.

[CraigD]

12:12 and a bit. I know you meant to say a touch under the speed of light. :)

I was sticking with the original posts conditions, but you’re right, if we’re talking about real, material trains with type II+ civilization amounts of energy available (and a whimsical urge to realize technology that sensible people only talk about in thought experiments), the train’s speed must a tad under c. The only way you can have lightspeed travel is if you’re actually using lightspeed communications (which isn’t innately very high tech) to send data from place to place, and “travel” involves installing a copy of yourself into a computer/robot at your destination – pretty far-fetched cyberpunk, though IMHO not physically impossible, stuff.

 

Nothing in this question requires any use of relativity. Here’s one that does:

• Xyz’s friend gets on the train, which departs “next station” at 12:10 PM and, traveling instantly at the speed of light, arrives at “departure station” at 12:18 PM (according to xyz’s clock).
• Xyz and his friend meet 2 minutes later. Xyz’s clock reads 12:20 PM.
• What does his friend’s clock read?

If I was at Shady grove and my friend was at Tautarus, both our clocks synchronised, my friends clock would show the same time as my clock on the arrival (ignoring the ''time'' dilation).

But you can’t ignore time dilation with a question about the real universe. Only in space opera/fantasy can we just ignore proven science.

 

The correct answer (Which A-wal gave) is that the friend’s clock would read 12:12 PM, 8 minutes earlier than xyz’s clock.

 

People who travel a lot at substantial fractions of c would need to synchronize their clocks at their destinations. I imagine this would be so automatic that people wouldn’t be aware of it, just as we don’t give much thought to why the clocks on our cellphones are never inaccurate, and via the same mechanism – ubiquitous wireless communication networks.

 

At the risk of being pedagogic, here’s the same question, but in this case where the train (unrealistically) instantly accelerates to 0.99 c (as measured by the stations) at Tartarus and instantly to 0 at Shady Grove. What would xyz’s friend’s clock read when Xyz’s clock reads 12:20 PM?

[A-wal]

Is xyz; 1) At Tartarus and stays there, 2) Starts at Tartarus and travels on the train to Shady Grove, 3) At Shady Grove from the start. And the same for Xyz.

[xyz]

Nothing's moving at half speed. It takes 8 minutes for the traveler to make the trip between the earth and sun and a further 8 minutes for the light to travel back to the staring point so the trip is completed in 8 minutes on a clock at the destination and 8 minutes after that on a clock at the starting point. It takes no time at all on the travelers clock because they're moving at the speed of light.

 

It's only "already here" after the 8 minutes it takes to travel from the sun to the earth.

I am sorry I really want to understand this but I am not understanding you.

 

 

Ok, I am standing on Earth looking at the Rocket, it takes relatively no time at all for the light to reach my eyes because I am close to the rocket. 

 

The rocket takes off at 12:00 and travels at c for 2 minutes , a 1/4 of the journey, the light is taking two minutes to reach my eyes from the rocket , both my clock and the on-board rocket clock show exactly 12:02

 

OK ?. 

[A-wal]

Nope. Time isn't moving at all for the on board clock. Time dilation (and length contraction) are infinite at the speed of light so a trip of any distance happens instantly from the perspective of the traveler. The space is halved and time moves at half rate at 0.8 the speed of light so it might be easier to use that speed.

[xyz]

Nope. Time isn't moving at all for the on board clock. Time dilation (and length contraction) are infinite at the speed of light so a trip of any distance happens instantly from the perspective of the traveler. The space is halved and time moves at half rate at 0.8 the speed of light so it might be easier to use that speed.

What?  are you trying to say that a person would not age at all if they travelled at c?

 

Added - and you are saying time stops for light  when light is travelling

Edited July 9, 2016 by xyz

[A-wal]

It's impossible for a massive object to travel at c so time will always pass but yes, time dilation approaches infinity as you approach c.

 

Yes, time stops for light. From light's frame of reference the universe is a spatial and temporal singularity (the only form of singularity imo because you can't have length contraction without time dilation but I digress).

[xyz]

It's impossible for a massive object to travel at c so time will always pass but yes, time dilation approaches infinity as you approach c.

 

Yes, time stops for light. From light's frame of reference the universe is a spatial and temporal singularity (the only form of singularity imo because you can't have length contraction without time dilation but I digress).

So you are claiming while the Universe continues forward in time that the object travelling at c does not experience time and time stops for the object, so how do you assume that speed in any way affects time?

 

I am sorry but you are sounding rather subjective and not objective. 

 

 

added - I have thought some more about this , I have failed to explain the third observer and what they observe relative to them. 

 

https://www.youtube.com/watch?v=oLKVSOUnsVM

 

This reminded me of the above video I made a while ago, the above video represents our scenario.

 

Further added - the third observer, A-wal is an equal distance apart from Tartaurus and Shady grove, where xyz and Craig are ''pinging''' and ''ponging'' between destinations.  A-wal is the equivalent of 8 minutes away from each destination, 

 

 

A-wal experiences an infinite speed of causality, an infinite speed because the visual line of sight is ''gin-clear'' and the speed of sight is infinite. 

Edited July 10, 2016 by xyz

[A-wal]

So you are claiming while the Universe continues forward in time that the object travelling at c does not experience time and time stops for the object, so how do you assume that speed in any way affects time?

No, no object can ever reach the speed of light relative to any other object because the energy needed to accelerate an object that's already moving in your own frame of reference increases as the object's relative velocity increases and at an ever increasing rate the closer it gets to the speed of light in exactly the same way that time time dilation and length contraction increase as an ever increasing rate the closer an object gets to the speed of light.

 

The fact that you can't comprehend the model doesn't in any way negate it's validity, it only negates your nonsensical BS.

 

I am sorry but you are sounding rather subjective and not objective.

No I'm not. What I'm describing is an objective description of reality that's proven by the fact the speed of light is the same in all inertial frames of reference.

 

Further added - the third observer, A-wal is an equal distance apart from Tartaurus and Shady grove, where xyz and Craig are ''pinging''' and ''ponging'' between destinations.  A-wal is the equivalent of 8 minutes away from each destination, 

 

 

A-wal experiences an infinite speed of causality, an infinite speed because the visual line of sight is ''gin-clear'' and the speed of sight is infinite. 

That makes no sense. An observer at an equal distance between the two points would be four minutes away from both and could only make instantaneous observations as the trains pass by, at other times the observations will be delayed by the time it takes for the light to reach the observer.

 

All you do is repeat the same crap over and over. You're not worth talking to, go away.

 

 

At the risk of being pedagogic, here’s the same question, but in this case where the train (unrealistically) instantly accelerates to 0.99 c (as measured by the stations) at Tartarus and instantly to 0 at Shady Grove. What would xyz’s friend’s clock read when Xyz’s clock reads 12:20 PM?

Is xyz; 1) At Tartarus and stays there, 2) Starts at Tartarus and travels on the train to Shady Grove, 3) At Shady Grove from the start. And the same for Xyz.

I got one. Two observers with their watches in synch (from the perspective of an observer half way between them), one observer at each station, one takes the instantly accelerating train to meet the other observer. The traveler's watch is 6 minutes behind the other observer's watch after the journey. How fast did the train move in the station's reference frame?

Edited July 10, 2016 by A-wal