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tommac
2008-Nov-03, 03:33 PM
I am not sure where this question is going and I am pretty sure that my terminology is wrong. But let me at least start and I will correct my question as we go along.

Say a spaceship was travelling at near the speed of light relative to us.
Now inside of the spaceship you have wires that provide energy to the engine that is under the hood in the front of the space craft. The space craft is travelling directly away from us and towards its "front" ( the engine is the farthest point away from us, the rest of the spaceship closer ).

Without energy ( electricity ) the engine can not work.

When the spaceship accelerates and now is near the speed of light, the electrons in the spaceship still need to move around ( at the local speed of light ) and drift towards the front at a rate suffient enough to power the engines. However since it moving at near the speed of light I would think that the natural tendency of the electrons would drift backwards towards us.

Another way to look at this is that electrons move around in somewhat arbitrary motion at the speed of light, the drift usually would push from source to sink, however since it is travelling at the speed of light wouldnt an artificial sink be produced?

01101001
2008-Nov-03, 03:47 PM
When the spaceship accelerates and now is near the speed of light [...]

Relative to what?

tommac
2008-Nov-03, 04:09 PM
Relative to what?


Say a spaceship was travelling at near the speed of light relative to us.

Relative to any observer really.

Jeff Root
2008-Nov-03, 04:28 PM
The speed of the spacecraft (relative to us or anyone else) has no
effect on the motion of electrons or anything else in the spacecraft.

-- Jeff, in Minneapolis

tommac
2008-Nov-03, 04:38 PM
The speed of the spacecraft (relative to us or anyone else) has no
effect on the motion of electrons or anything else in the spacecraft.

-- Jeff, in Minneapolis

Huh ? So only the outside is relative to us? But the inside doesnt count?

What if the wires were on the outside?

mugaliens
2008-Nov-03, 05:08 PM
The spaceship's length is contracted along it's relative velocity vector. To the electrons on board, however, if they had to travel 30' to get from the battery to the engine before, they have 30' to travel now.

NEOWatcher
2008-Nov-03, 05:12 PM
Huh ? So only the outside is relative to us? But the inside doesnt count?
It's not really a matter of inside/outside, it's more of a matter of the velocity is the same as the spacecraft (for both the outside observer and the inside observer).
Same speed, same clock.
Different observers, different clocks and different yardsticks. But; SOL observed the same.

tommac
2008-Nov-03, 05:13 PM
The spaceship's length is contracted along it's relative velocity vector. To the electrons on board, however, if they had to travel 30' to get from the battery to the engine before, they have 30' to travel now.

The electrons need to travel in the direction of travel which is directly away from the observer.

The thing is that this is similar to the flashlight on a train right except that our perception of the electrons movement would be a drift back in our direction as compared to the rest of the spacecraft.

tommac
2008-Nov-03, 05:18 PM
It's not really a matter of inside/outside, it's more of a matter of the velocity is the same as the spacecraft (for both the outside observer and the inside observer).
Same speed, same clock.
Different observers, different clocks and different yardsticks. But; SOL observed the same.

OK let me go over one more time.

We are the observer located somewhere behind the spaceship the engine is in the front of the spaceship and the battery is in the back of the ship ( aft or whatever ) ... the electricity needs to move from the back of the ship to the front of the ship. As the spaceship moves near teh speed of light. Each electron moving in a random / arbitrary direction would from our vantage point not be able to move very fast or maybe not at all towards the front of the ship ( because of relativity (for example the light shiningfrom a train moving at the speed of light example ) , however it could move freely and even accelerated towards the back of the spacecraft. All of this from our vantage point.

Now inside the ship, you have a battery which pushes the electron drift towards the engine and everything is fine and normal.

From OUR vantage point the electricity would appear to be running in reverse current.

NEOWatcher
2008-Nov-03, 05:32 PM
... Each electron moving in a random / arbitrary direction would from our vantage point not be able to move very fast or maybe not at all towards the front of the ship ( because of relativity (for example the light shiningfrom a train moving at the speed of light example ) , however it could move freely and even accelerated towards the back of the spacecraft. All of this from our vantage point. ...
That's the problem.
On the spaceship, the electron has gone from a speed of zero*, to a speed of C no matter which direction it is going.
Off the spaceship, the electron has gone from a speed* of <C to a speed of C.

In other directions, the only thing that changes is the angle of the electron moving away from the observer. It is still C for either.

*I know electrons aren't really zero, but localized to a battery, you can effectively call it zero for this example.

tommac
2008-Nov-03, 06:03 PM
Off the spaceship, the electron has gone from a speed* of <C to a speed of C.

Still confused. Off the spaceship, the electron goes from <C to C in the direction of motion and goes from -<C to C =~ delta 2C in the opposite direction.

Spaceship ----->

E1 <-------------Spaceship->E2


E2 electron when moving with the direction of the spaceship
E1 when moving oposite of the spaceship

E1 > E2

All other angles will follow a percentage of this tendency. with 90% moving with the speed of the spaceship.

Electrons would be flying off the back of the spaceship.

John Mendenhall
2008-Nov-03, 06:10 PM
(snip)

From OUR vantage point the electricity would appear to be running in reverse current.



Why would you think that? A fundamental part of relativity is that after applying the appropriate math, all observers can agree about what is happening.

In general, be cautious about 'thought experiments'. It's the devil to see what's wrong with them if they are not very carefuly constructed at the outset. That's what 0110etc's comment is about. And, for example, there is an opportunity here in your question to open the door to rigidity, inertia, and reference frame questions, which the big guys are still arguing about.

Briefly, the electrons in the conducting cable are not sloshing around like a liquid, and could care less how fast the ship is going., and for that matter, the real liquid(s) in the plumbing will behave the same way. Remember, even under acceleration, the reaction is the same as in a gravitational field, and we do not have to stir the electrolyte in our car batteries to get the electrons off the bottom before starting (double rear window VW's of the '50's don't count).

tommac
2008-Nov-03, 06:20 PM
Really the wire part doesnt matter all of that much. We can take any electron in or on the spaceship. Let me re-ask the question.

How does an electron act relative to an observer that is travelling at relativistic speeds towards or away from it? This assumes that the electron will spend some time moving towards the observer and other time moving away from the observer. ( and other times moving perpendicular to the observer etc ... )

The electron can not travel much faster in one direction.

Would the electron slow down in all directions? ( I dont think this can be accomplished without having 3d time ).





Why would you think that? A fundamental part of relativity is that after applying the appropriate math, all observers can agree about what is happening.

In general, be cautious about 'thought experiments'. It's the devil to see what's wrong with them if they are not very carefuly constructed at the outset. That's what 0110etc's comment is about. And, for example, there is an opportunity here in your question to open the door to rigidity, inertia, and reference frame questions, which the big guys are still arguing about.

Briefly, the electrons in the conducting cable are not sloshing around like a liquid, and could care less how fast the ship is going., and for that matter, the real liquid(s) in the plumbing will behave the same way. Remember, even under acceleration, the reaction is the same as in a gravitational field, and we do not have to stir the electrolyte in our car batteries to get the electrons off the bottom before starting (double rear window VW's of the '50's don't count).

grant hutchison
2008-Nov-03, 07:09 PM
Tommac, the foundation of special relativity is that electromagnetic phenomena work the same for all observers, independent of their state of motion. So that answers your question: electricity works just fine aboard the ship, in a way indistinguishable from electricity anywhere else.

Your specific question about a free electron in motion within the ship is one about addition of velocities under special relativity. The electron can move relative to the ship with any velocity less than lightspeed, in any direction. An outside observer will, in general, measure its velocity in one direction as being different from its velocity in another direction. The electricity will work properly in either case.

Please don't try to get into a discussion of your notion of 3D time in Q&A.

Grant Hutchison

Hornblower
2008-Nov-03, 07:12 PM
tommac,

Various responders have answered your questions as clearly as I could have, if not better, and yet you persist in believing that our perception of an object's direction of motion in the spacecraft would be reversed if the spacecraft is receding from us fast enough.

I conclude from this and from many other of your posts that your understanding of the basic physics is very deficient, to an extent that cannot be corrected by short answers in a forum such as this one. I would recommend that you study some good textbooks on the topics involved. There are people in this forum who can make some good specific recommendations.

By the way, electrons in a typical circuit driven by a battery or a generator do not travel anywhere near the speed of light.

mugaliens
2008-Nov-03, 07:16 PM
...our perception of the electrons movement would be a drift back in our direction as compared to the rest of the spacecraft.

No, it would not.

Hornblower
2008-Nov-03, 07:21 PM
Here is a follow-up, after reading the following article:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html

The electrons in a wire jiggle at high speed, but only a very small fraction of c. With no voltage along the wire, their mean position is virtually stationary.

When a current is flowing, a drift velocity is superimposed on the jiggling motion. This drift velocity is very slow, perhaps millimeters per second in a typical case.

tommac
2008-Nov-03, 09:35 PM
Here is a follow-up, after reading the following article:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html

The electrons in a wire jiggle at high speed, but only a very small fraction of c. With no voltage along the wire, their mean position is virtually stationary.

When a current is flowing, a drift velocity is superimposed on the jiggling motion. This drift velocity is very slow, perhaps millimeters per second in a typical case.

Yes this is the drift velocity. However the jiggle is at speeds close to C.
They are at the speed of the electron. The drift is slow but the electrons in the wire are moving quickly.


Take a hose of water for example. If you turn on the water for an empty long hose it will take some time for the water for flow through the hose and come out the other end. If you fill the hose then turn on the water, it will take about the speed of sound in water of latency before the water comes out of the other end of the hose.

It is very similar for electron drift. You have a wire, you put an electron on the wire and at near speed of light an electron comes out of the other end of the wire ... the catch is that it is not the same electron. The time it takes the electron that you put on one end of the wire to come out the other side is very slow and that is the drift.

This drift is from a lower potential on one side than the other ( I think ).

The analogy from my school was the drunk man on a hill. The drunk man stumbles in a random direction. But since there is a hill it is more likely that he will stumble in the downward direction than an upward direction.

In my example above the electrons from a distant observer would all be more likely to travel to the rear direction of the spaceship. When aboard the spaceship the electrons are travelling stumbling towards the front.

tommac
2008-Nov-03, 09:43 PM
Please don't try to get into a discussion of your notion of 3D time in Q&A.


I appologize, I just hinted at it in my state of confusion.

What I am confused about is the microscopic phenomena within the macroscopic object moving at relativistic speeds.

I may have confused it in my wording. What I am asking is:

If electron movement is arbitrary around a nucleus and the nucleus is travelling at relativistic speeds does how is the electron movement effected in order not to violate the laws of special relativity?

captain swoop
2008-Nov-03, 10:52 PM
After all these months and innumerable questions you still seem to have a basic misunderstanding of physics. Either that or you are subtly trying to push an ATM concept.

Please take Hornblowers advice, you can't get a physics education via questions on an Internet forum.

Hornblower
2008-Nov-03, 11:03 PM
Yes this is the drift velocity. However the jiggle is at speeds close to C.
They are at the speed of the electron. The drift is slow but the electrons in the wire are moving quickly.


Take a hose of water for example. If you turn on the water for an empty long hose it will take some time for the water for flow through the hose and come out the other end. If you fill the hose then turn on the water, it will take about the speed of sound in water of latency before the water comes out of the other end of the hose.

It is very similar for electron drift. You have a wire, you put an electron on the wire and at near speed of light an electron comes out of the other end of the wire ... the catch is that it is not the same electron. The time it takes the electron that you put on one end of the wire to come out the other side is very slow and that is the drift.

This drift is from a lower potential on one side than the other ( I think ).

The analogy from my school was the drunk man on a hill. The drunk man stumbles in a random direction. But since there is a hill it is more likely that he will stumble in the downward direction than an upward direction.

In my example above the electrons from a distant observer would all be more likely to travel to the rear direction of the spaceship. When aboard the spaceship the electrons are travelling stumbling towards the front.
Your reasoning continues to be a mystery to me. Suppose the electrical system is such that the crew sees the electrons jiggling, and drifting away from the tail and toward the nose. If I could observe the electrons from afar as the craft runs away at close to c, I would expect to see them jiggling and drifting more slowly as a result of the time dilation, but the drift still would be toward the nose. Please explain in appropriate detail why you think otherwise.

tommac
2008-Nov-04, 03:27 PM
Your reasoning continues to be a mystery to me. Suppose the electrical system is such that the crew sees the electrons jiggling, and drifting away from the tail and toward the nose. If I could observe the electrons from afar as the craft runs away at close to c, I would expect to see them jiggling and drifting more slowly as a result of the time dilation, but the drift still would be toward the nose. Please explain in appropriate detail why you think otherwise.

OK at least I think we are on the same page now. Thanks for being patient.

And I just need to note that my suggestion of 3d time stems from a clear confusion about time-dilation. So I need again to delve into this clarification in hopes of not agitating people who will jump at the chance of saying I am trying to promote ATM here.

As the space ship moves near the speed of light it will stretch in the direction of motion and you will have dilated time to keep the speed of light constant.

There is no stretching / contracting in the perpendicular directions.

( am I right so far? )

Say we have two flashlights one pointing foward and one backwards ( stern/aft ) The light shining forwards is travelling slower relative to the speed of the spaceship from our view point than the light from the aft.
t1 dSLaft=0 dSLstern=0
x---LightLight---x
x---Spaceship---x
t2 dSLaft=2 dSLstern=0
x--Light--Light--x
x----Spaceship--x
t3 dSLaft=4 dSLstern=0
x-Light----Light-x
x-----Spaceship-x
t4 dSLaft=6 dSLstern=0
xLight------Lightx
x------Spaceshipx

So time needs to move faster in the region towards the aft and slower in the region towards towards the stern. In order for light to appear that it is moving at the speed of light relative to it. Are we in agreement here? Or am I lost? If time slows everywhere then the light moving off the aft will not be able to be kept constant.

Lets start with this small point and we can discuss more. Please let me know if we are in agreement.

Jeff Root
2008-Nov-04, 04:50 PM
Tom,

"Aft" means "at, near, or toward the stern". In the rear. The bow is forward.

-- Jeff, in Minneapolis

hhEb09'1
2008-Nov-04, 05:43 PM
This drift is from a lower potential on one side than the other ( I think ). From high, to low. Think, waterfall. :)

The analogy from my school was the drunk man on a hill. The drunk man stumbles in a random direction. But since there is a hill it is more likely that he will stumble in the downward direction than an upward direction.On a hill he won't stumble in a totally random direction. Or is that what you mean?

In my example above the electrons from a distant observer would all be more likely to travel to the rear direction of the spaceship. When aboard the spaceship the electrons are travelling stumbling towards the front.Why would they be more likely?

Jeff Root
2008-Nov-04, 06:00 PM
Tom,

To simplify your question, can you have the spaceship just coasting at
whatever speed, not accelerating? You could still have electrons moving
around doing something other than running the engine. There may be a
complication if the spaceship is accelerating.

-- Jeff, in Minneapolis

hhEb09'1
2008-Nov-04, 06:07 PM
From my reading of the OP and followups, I assumed that we were talking about observations once speed had been obtained, rather than during the acceleration.

Ken G
2008-Nov-04, 06:49 PM
If the speed has already been attained, then the answer is very straightforward. You start by noting that for the observer in the ship, the circuit is performing perfectly normally, in every way. Then to transform to observers outside the ship, you just subtract the velocity of the observer from the instantaneous velocity of every electron, but you do that in the relativistic way of combining velocities, such that no velocities ever exceed c. This is also what grant hutchison said. Yes, the direction of the electron motion can change for outside observers, but the action of the current will not change at all-- the outside observer will always be able to transform back to the on-board frame, and in so doing will always see a perfectly normal circuit.

If you fly over a football game in a high-speed aircraft, the game may look a bit odd at first, what with all those people running backward and so forth, but your mind will quickly understand that a perfectly normal football game is being played there. Relativistic corrections do not change that basic truth-- indeed, preserving that truth is the whole purpose of relativistic corrections.

tommac
2008-Nov-04, 07:27 PM
Tom,

"Aft" means "at, near, or toward the stern". In the rear. The bow is forward.

-- Jeff, in Minneapolis


Hah ... OK cool! Good thing I dont drive a boat.

tommac
2008-Nov-04, 07:30 PM
From high, to low. Think, waterfall. :)On a hill he won't stumble in a totally random direction. Or is that what you mean?Why would they be more likely?

Well what I was thinking at the time was the the electrons relative to us would travel in the rear direction at a speed of 2x the speed of light away from the ship while not travelling much at all in the direction of the BOW.

Similar to shining a light in the front and the back of a train moving relativistically.

tommac
2008-Nov-04, 07:31 PM
Yes, thanks ... I way over complicated the question and I agree with the simplification below.


Tom,

To simplify your question, can you have the spaceship just coasting at
whatever speed, not accelerating? You could still have electrons moving
around doing something other than running the engine. There may be a
complication if the spaceship is accelerating.

-- Jeff, in Minneapolis

tommac
2008-Nov-04, 07:32 PM
From my reading of the OP and followups, I assumed that we were talking about observations once speed had been obtained, rather than during the acceleration.

The OP was about non-acceleration at speeds of near the speed of light.
But we can discuss acceleration also.

tommac
2008-Nov-04, 07:36 PM
Yes, the direction of the electron motion can change for outside observers, but the action of the current will not change at all-- the outside observer will always be able to transform back to the on-board frame, and in so doing will always see a perfectly normal circuit.
.

This is my question. How can electrons have a tendency to move to the aft and still show a current moving forward.

In fact if the space ship was moving at the speed of light could current even move forward?

NEOWatcher
2008-Nov-04, 07:36 PM
Well what I was thinking at the time was the the electrons relative to us would travel in the rear direction at a speed of 2x the speed of light away from the ship while not travelling much at all in the direction of the BOW.
Are you still thinking that way?

We percieve a difference of 2x, but from our perspective nothing is past the value of C. It's only a mathematical 2x that doesn't translate to anything physical.

And yes, the difference is much larger than the one going forward. Why? because it's going much slower reletive to us than the one going forward.

Now; to someone on the ship, and physically to the ship, everything is normal.

tommac
2008-Nov-04, 07:38 PM
On a hill he won't stumble in a totally random direction. Or is that what you mean?

flat surface = totally random.
hill would provide a tendency to move downwards. The analogy was supposed to show the concept of electron drift on some level or another.

when you increase the current the hill becomes steeper I think.

tommac
2008-Nov-04, 07:40 PM
Are you still thinking that way?

not sure




We percieve a difference of 2x, but from our perspective nothing is past the value of C. It's only a mathematical 2x that doesn't translate to anything physical.


Well we do see the ship and the light seperating at the speed of 2x the speed of light. However neither relative to us travels at faster than c.

NEOWatcher
2008-Nov-04, 08:01 PM
Well we do see the ship and the light seperating at the speed of 2x the speed of light. However neither relative to us travels at faster than c.
Exactly.

thorkil2
2008-Nov-05, 09:00 AM
Only read part of this, so maybe someone else has pointed out that electrons do not move through a wire at the speed of light. Electrons drift at a much slower rate; electric current is carried by electric fields that move through the wire at something like c. All the laws of physics apply in the same way within a given inertial frame of reference. It doesn't matter how fast the ship is going. What happens inside (meaning inside the moving frame) happens as though the frame were at rest. Inside/outside the ship's shell is irrelevent. If the wires are moving with the ship, then they behave for your measuring instruments inside that frame as though everything was at rest.

captain swoop
2008-Nov-05, 10:19 AM
If the wires are moving with the ship, then they behave for your measuring instruments inside that frame as though everything was at rest.


This, as always seems to be the sticking point.

tommac
2008-Nov-05, 02:57 PM
Only read part of this, so maybe someone else has pointed out that electrons do not move through a wire at the speed of light. Electrons drift at a much slower rate; electric current is carried by electric fields that move through the wire at something like c. All the laws of physics apply in the same way within a given inertial frame of reference. It doesn't matter how fast the ship is going. What happens inside (meaning inside the moving frame) happens as though the frame were at rest. Inside/outside the ship's shell is irrelevent. If the wires are moving with the ship, then they behave for your measuring instruments inside that frame as though everything was at rest.


I think this was addressed in the original post and then again in depth with the drunk on a hill analogy.

Ken G
2008-Nov-05, 09:31 PM
This is my question. How can electrons have a tendency to move to the aft and still show a current moving forward.
The answer has no direct connection with relativistic corrections-- it all depends on what you mean by "move to the aft". Let's take my football analogy. If you fly over a stadium, and look down and see a runner in the open field heading toward the end zone, it might appear that they are moving backward because your plane is moving faster forward than they are. You might as well ask, "how can that person score a touchdown if they are moving away from the direction of the end zone?" The answer is, they can because the end zone is also moving in that direction, even faster.


In fact if the space ship was moving at the speed of light could current even move forward?There is no such thing as "moving at the speed of light", because it might be the observer zooming past at that speed (or nearly that speed). If you are eating breakfast at your table, and an alien in outer space zooms past at the speed of light (never mind this is not literally possible), does that interfere with your breakfast? Relativity in the absence of acceleration is never about what happens, it is always about what happens in one frame as seen from another frame. (If there is acceleration, you may have to worry about what the acceleration is doing and how it is accomplished.)

tommac
2008-Nov-05, 10:13 PM
The answer has no direct connection with relativistic corrections-- it all depends on what you mean by "move to the aft". Let's take my football analogy. If you fly over a stadium, and look down and see a runner in the open field heading toward the end zone, it might appear that they are moving backward because your plane is moving faster forward than they are. You might as well ask, "how can that person score a touchdown if they are moving away from the direction of the end zone?" The answer is, they can because the end zone is also moving in that direction, even faster.

I think I get where you are going and I think I am starting to understand the whole point. I realize that they are part of the system.

Lets take the football analogy above and lets say I see thomas Jones rushing into the end zone for a touchdown as I am travelling at a snails pace slower than the speed of light. In this case thomas jones would need to be time dialted in order to run into the end zone and the distance would be also proportionally skewed. so that should mean that the whole field should be time dialated. However I note that people that are running from sideline to sideline dont have the elongated field. Are they still time dialated?

Ken G
2008-Nov-05, 10:36 PM
Lets take the football analogy above and lets say I see thomas Jones rushing into the end zone for a touchdown as I am travelling at a snails pace slower than the speed of light. In this case thomas jones would need to be time dialted in order to run into the end zone and the distance would be also proportionally skewed. Yes, from my perspective, there would be three things happening. The field would be much shorter, the game clocks would be running very slowly, and the clocks at opposite ends of the field would be badly unsynchronized with each other (you need that last effect to make things work out).
However I note that people that are running from sideline to sideline dont have the elongated field. Are they still time dialated?Yes, they would appear to the alien zooming by to take much longer to go sideline to sideline than they think they take, or is read on the sideline clocks. But the alien would also think they are moving very slowly in the sideline-to-sideline direction, as most of their speed would be along the direction of motion of the alien (and the vector sum cannot exceed c).

You may take heart in the fact that all your difficulties stem from the fact that you have chosen the most difficult constant-speed problem of all-- that of motion on a field that is itself moving relativistically relative to an observer.

tommac
2008-Nov-06, 03:14 PM
I must appologize in advance here so as not to be accused of heading to ATM by some questionable intellegent life forms on this board.

But I would like to ask a few more questions as this is still where I get stuck.

Lets take the same setup.
We have 4 people on the field running in different directions 90% angles to each other starting at the same point and running all at the exact same speed on the ground.

One direction is in the direction of our movement. Two perpendicular and one in the opposite direction of our movement.

Our perception for each one would be? ( the two perpendicular would obviously be the same as each other so lets just go over the three scenerios )

1) in the direction ... we see him running slower and running a shorter distance.
2) in the opposite direction ... we see him running faster than #1 and running a longer distance.
3) perpendicular .... we see him running somewhere in between the two speeds 1 and 2 and its distance would be the same as on the field right?

Is this correct?


Yes, from my perspective, there would be three things happening. The field would be much shorter, the game clocks would be running very slowly, and the clocks at opposite ends of the field would be badly unsynchronized with each other (you need that last effect to make things work out).Yes, they would appear to the alien zooming by to take much longer to go sideline to sideline than they think they take, or is read on the sideline clocks. But the alien would also think they are moving very slowly in the sideline-to-sideline direction, as most of their speed would be along the direction of motion of the alien (and the vector sum cannot exceed c).

You may take heart in the fact that all your difficulties stem from the fact that you have chosen the most difficult constant-speed problem of all-- that of motion on a field that is itself moving relativistically relative to an observer.

NEOWatcher
2008-Nov-06, 03:34 PM
The part about side-to-side that I get lost in is the part about the vector that is observed.
Any side-to-side movement (naturally involving time), means that the moving observer has a constantly changing direction and distance to the runner.
So; I find it very hard to understand if the observer can even detect if the runner's angle is 90 degrees because everything is going to be a changing curve.

Ken G
2008-Nov-07, 01:03 AM
I1) in the direction ... we see him running slower and running a shorter distance.
2) in the opposite direction ... we see him running faster than #1 and running a longer distance.
3) perpendicular .... we see him running somewhere in between the two speeds 1 and 2 and its distance would be the same as on the field right?
It depends a lot on what you mean by the distance they run. Most people would say the distance they run is a distance relative to the field, not a distance relative to the spacecraft (because even someone not running at all moves a distance relative to the spacecraft.

tommac
2008-Nov-07, 03:15 PM
It depends a lot on what you mean by the distance they run. Most people would say the distance they run is a distance relative to the field, not a distance relative to the spacecraft (because even someone not running at all moves a distance relative to the spacecraft.


distance relative to the field as perceived by the spaceship. My question is if you have time dilation then travel in any of the directions need to be at the same relative rate keeping c always constant. This is the root of all of my questions and what eventually gets me digging into ATM ... my ( I guess ) misunderstanding of this concept.

Ken G
2008-Nov-07, 06:29 PM
I1) in the direction ... we see him running slower and running a shorter distance. To define a velocity, you need both a time and a distance. It sounds like you want to mark two points on the field where the runner begins and ends, and then ask, how far apart are those points in the rocket frame, and how much time elapsed in the rocket frame. These are the kinds of things you have to be very clear about in relativity. There are three things you have to do to calculate the answers to your questions:
1) length contract the distance between the marks, by the Lorentz factor of the rocket's speed relative to the field. So if the Lorentz factor is, say, 1000, and the runner thinks the marks are 100 yards apart, the rocket thinks they are 0.1 yards apart.
2) time dilate the clocks on the field by that same factor. So if a clock carried by the runner ticks off 10 seconds during that run, in the rocket frame that will be interpreted as 10,000 seconds. The field will now be close to 10,000 light seconds in distance behind the rocket, from the rocket's perspective. The runner, when he/she finishes the run, will think the rocket is only about 10 light seconds away. The rocket will have a different concept of when that time is.
3) assert that clocks at each end of the field are not synchronized. This will account for the fact that the runner's watch will agree with both clocks, even though he is moving at a speed different from that of the field (so we'd need a different Lorentz factor to calculate his time dilation). This is a negligible effect since the runner is not moving at anywhere near the speed of light, so you can ignore step 3 (but do so at your peril in more general situations).

When you do all this, you find that the runners going along and against the direction of the rocket are perceived as running, in rocket time and relative to the field, at a speed 1,000,000 times smaller than the runner thinks they are running at. The runners going perpendicular to the motion of the rocket are perceived as running 1,000 times slower than they perceive themselves as running, all assuming the Lorentz factor of the rocket motion is 1,000. If these numbers seem odd, it is simply because this is a rather strange way to interpret the meaning of running speed. More likely, the rocket observer would transform the distances and the times into the frame of the runner, and doing so would arrive at the usual expected result for running speed in any direction.

Hornblower
2008-Nov-07, 07:58 PM
distance relative to the field as perceived by the spaceship. My question is if you have time dilation then travel in any of the directions need to be at the same relative rate keeping c always constant. This is the root of all of my questions and what eventually gets me digging into ATM ... my ( I guess ) misunderstanding of this concept.
I don't think there is any shame in misunderstanding this stuff. I was a physics major in college before Uncle Sam changed me to a career military bandsman, and I still am not proficient in it. What I did learn is that we must trust the math as developed by Lorentz, Einstein, et. al., no matter how counterintuitive it may seem to a novice. It has withstood the tests applied to it by the experts for a century now.

cosmocrazy
2008-Nov-07, 11:00 PM
Just a little thought, when the spaceship reaches C then distance traveled & time elapsed are perceived by those on board (in their reference frame) to be zero. So in a sense the current wouldn't flow anyway?

Hornblower
2008-Nov-08, 01:25 AM
Just a little thought, when the spaceship reaches C then distance traveled & time elapsed are perceived by those on board (in their reference frame) to be zero. So in a sense the current wouldn't flow anyway?
The spaceship will not reach c, if Einstein and company were right. The theory has withstood a multitude of tests for a century.

cosmocrazy
2008-Nov-08, 11:24 PM
The spaceship will not reach c, if Einstein and company were right. The theory has withstood a multitude of tests for a century.

Exactly. :)

Digix
2008-Nov-09, 12:55 AM
I see most of such questions assume that some spaceship can theoretically fly at the speed of light, but that is impossible.

So everything will be very simple spaceship speed and whatewer inside speed will just sum in relativistic way.
example if spaceship is going at 0.9C and something inside also goes at 0.9C then we would see that that something is going relatively to us at 0.95C however to spaceship pilot it still moves at the speed pf 0.9C

papageno
2008-Nov-15, 04:13 PM
Say a spaceship was travelling at near the speed of light relative to us.
Now inside of the spaceship you have wires that provide energy to the engine that is under the hood in the front of the space craft. The space craft is travelling directly away from us and towards its "front" ( the engine is the farthest point away from us, the rest of the spaceship closer ).


From a quick reading of the thread, it appears that a point has not been clarified: the energy to power the engine is not transported by the electrons in the wire. The energy is transported by the electric field in the space around the wires (see Feynmann's Lectures on Physics). The wires are a convenient way to control the electric field, but the electrons in normal conductors are actually wasting the energy of the electric field (Joule effect).