# Thread: A relative speed of light problem?

1. He was a great mind

It was the facts. It was experimentally proven before that the speed of light is the same no matter in what direction the observer travels relatively to the light.
All the rest is a consequence of this. Of course it took a great mind to derive all that.

2. It was a classic case of Occam's razor. Note that no experiment actually showed that the speed of light is invariant, rather they could all be understood by adopting that axiom. Nevertheless, it is an axiom, and is never proven to be true-- all we ever get to know is that it works and is simple. When the place where it doesn't work is discovered, it will take science all of two seconds to think that everyone who believed relativity was absolute was making the same naive mistakes as all of their forefathers. And so it goes. What we can say is that relativity is a wonderful theory that works amazingly well, and that was the goal all along.

3. Originally Posted by Confunded
If information can travel faster than the speed of light to an observer; that implies I can send e-mail at faster than the speed of light, or my computer can make calculations faster than light, or I can communicate with astronauts faster than the speed of light. Of course, I can't do those things now, but these things can only be invented if they're possible. Is it possible?
To an outside observer light travels at the speed of light, not any faster, not any slower. I was speaking as if you were the light itself. If you were a beam of light you would be God-like. All seeing and eternaly living, at least to you, not to an outside observer.

4. It's not as simple as "god is light". If you were a beam of light you would not be "god-like" in any way - in fact it would be almost the opposite situation.

Consider this: If you are a photon travelling at the speed of light, you experience no time between being emitted and being absorbed. As soon as you leave your source you arrive at your destination. You have no control at all. If you don't hit something and get absorbed, you will continue travelling until you do hit something, or you will travel forever, experiencing nothing, if you don't hit anything.

If, by somehow bypassing the laws of physics, a person managed to find some method of accelerating to the speed of light, they would never be able to stop again of their own volition. As soon as you reach the speed of light time stops for you. You cannot make a decision. If you are in a spaceship you cannot issue a command. The navigation computer would be frozen in time too, so it cannot stop you "automatically" as it cannot execute any commands. Once you reach the speed of light you are stuck there until you hit something. You might cross the universe, frozen in time, not experiencing any of it.

So your journey would be either:

"Engage light speed" and then SMACK! as you hit something.

or

"Engage light speed" and then nothing for eternity

Neither sounds very "god-like" to me. You would see nothing and even eternity would be over in an instant...

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Normally, I'd just dub traveling at the speed of light as unthinkable and incomprehensible. It makes little sense when time stops like that. Neither would it makes sense to use infinite energy to accelerate to that speed.

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Normally, I'd just dub traveling at the speed of light as unthinkable and incomprehensible. It makes little sense when time stops like that. Neither would it makes sense to use infinite energy to accelerate to that speed.

7. That makes sense speedfreek, except for the eternity would be over in an instant part, but I get what you are saying. I will have to ponder on this some more.

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Originally Posted by Freiddie
Information can't travel faster than c.
I knew someone would say that.

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I thought the trains were racing toward each other at 1.5c according to my perspective? Is this the case or not?

10. Originally Posted by Confunded
I thought the trains were racing toward each other at 1.5c according to my perspective? Is this the case or not?
Yes, if two trains, each travelling at 0.75c, race towards each other, from your perspective (as a 3rd person) they are travelling towards each other at 1.5c. This is correct. But you see nothing itself travelling at over the speed of light. Each train is only travelling at 75% of light-speed.

If you were on one of those trains however, sitting at the front and watching the other train travel towards you, it would not look like it was travelling towards you at 1.5c, and your train would not look like it was travelling towards the other at 1.5c. To an observer on one of the trains, the other train would be closing on them at something under the speed of light.

This is because those trains and everyone on them are subject to relativistic time-dilation and length contraction. For every minute that passes to the outside world (the 3rd person, observing both trains), something around only 40 seconds passes for the passengers on each train. The length of objects in their direction of motion (including the track in front of them) would also shrink, but light always travels at the same speed. This would result in them calculating that, if they were consider themselves at rest, the other train is heading towards them at less than the speed of light - the light from the other train would still reach them before the train does.

Nothing overtakes light!

11. Originally Posted by Arcane
That makes sense speedfreek, except for the eternity would be over in an instant part, but I get what you are saying. I will have to ponder on this some more.
Sorry, that was me being a little sensationalist there. What I should have said is

"Anything less than eternity would be over in an instant!".

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is the mass of an object traveling at the speed of light infinite and the speed 0????

"If information can travel faster than the speed of light to an observer; that implies I can send e-mail at faster than the speed of light, or my computer can make calculations faster than light, or I can communicate with astronauts faster than the speed of light. Of course, I can't do those things now, but these things can only be invented if they're possible. Is it possible?"

it is possible ,Somme lab deed it

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The problem with the whole "nothing can travel faster than the speed of light" thing is #1, it's misunderstood and most don't even try to explain why it is and #2 travel in the sense that most people are talking is restricted to 3D space. so...

#1. Nothing can travel faster than light because it is the way we measure.

Let say that you are at point A...and then you use a conventional drive method to travel 365x the speed of light to move exactly 1 light year away to pont B. Now assume someone is exactly 1 lightyear away. What would happen? The observer would see a streak from A to B a year later over the course of a single day.

To further complicate this if that same ship the next day were to go .5ly towards the viewer and make a C to D trip that is exactly 1ly in distance the viewer would see something rather funny.

6months+2 after the trip was made the viewer would see the C to D trip for a day, but at the same time the viewer would also see B to C over the course of the next 6months-1 day in reverse AND THEN the viewer would see the ship go from A to B over the course of a day.

So, how long did it take for that ship to make that journey and how do you measure that? According to the ship it only took 2.5 days to take that trip if you assume constant velocity and it went 2.5ly, but to the outside observer it took 1 year for that trip to occur and the velocity shifted. And then nothing can go faster than light would say that's impossible for that to have happened. It must have taken 2.5 years.

But that's not where the story ends either because the crew of that ship would track time differently as well which I don't know too much about so since we measure everything using light or in some way nothing can be measured to have gone faster than light even if we can mathematically figure out that that is not exactly true.

and #2. As I pointed out in another thread, if you simply move through a different dimension can reach places faster than light, but I'm not sure whether you would consider that traveling or moving as if that it s right you wouldn't move 3 dimensionally. You would simply remove yourself from one spot and then be in the other.

14. Originally Posted by Durakken
The problem with the whole "nothing can travel faster than the speed of light" thing is #1, it's misunderstood and most don't even try to explain why it is and #2 travel in the sense that most people are talking is restricted to 3D space. so...

#1. Nothing can travel faster than light because it is the way we measure.

Let say that you are at point A...and then you use a conventional drive method to travel 365x the speed of light to move exactly 1 light year away to point B. Now assume someone is exactly 1 light-year away. What would happen? The observer would see a streak from A to B a year later over the course of a single day.

To further complicate this if that same ship the next day were to go .5ly towards the viewer and make a C to D trip that is exactly 1ly in distance the viewer would see something rather funny.

6months+2 after the trip was made the viewer would see the C to D trip for a day, but at the same time the viewer would also see B to C over the course of the next 6months-1 day in reverse AND THEN the viewer would see the ship go from A to B over the course of a day.

So, how long did it take for that ship to make that journey and how do you measure that? According to the ship it only took 2.5 days to take that trip if you assume constant velocity and it went 2.5ly, but to the outside observer it took 1 year for that trip to occur and the velocity shifted. And then nothing can go faster than light would say that's impossible for that to have happened. It must have taken 2.5 years.

But that's not where the story ends either because the crew of that ship would track time differently as well which I don't know too much about so since we measure everything using light or in some way nothing can be measured to have gone faster than light even if we can mathematically figure out that that is not exactly true.

and #2. As I pointed out in another thread, if you simply move through a different dimension can reach places faster than light, but I'm not sure whether you would consider that travelling or moving as if that it s right you wouldn't move 3 dimensionally. You would simply remove yourself from one spot and then be in the other.
The main problem i see with this thought experiment is the fact that you are taking the constant "C" out of the scenario (my bold) as soon as you imply a greater than "C" then for any rest mass object GR becomes null and void. Using the theory of GR, for the crew aboard the space craft travelling between these points a,b,c & d the moment they reach the speed of light time and space becomes zero. (this was explained very well by Speedfreek in an earlier post). Regardless if the crew claimed to have gone faster than light the relative observers would only see them to be travelling at "C" over each given distance. They would measure 2.5years and the crew of the spaceship would measure zero (assuming they some how amazingly managed light-speed and also control the ship).
Using an extra dimension like you proposed before would make better sense.

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I forgot to mention that the energy to do it is also outside the realm of possibility, but anyways...

"Regardless if the crew claimed to have gone faster than light the relative observers would only see them to be travelling at "C" over each given distance."

I'm not sure you're disagreeing with what I said or not with this, but the reason the observer would see the path taken as only taking a day to go from A to B is because light is bounced from the ship from each position it was at during that day, even though it would be traveling faster, meaning that the light that bounced back would all reach the viewer during that day...

Of course this is just from practical knowledge...not math or GR. I don't know whether the light would be disrupted or not based on gravity generated...i would assuming traveling at that speed would create a lot and cause weird things to happen like you might see the bending of light from stars behind the ship and reflected light may reflect slower or faster off the hull...plus the time dilation may cause a small lag which could render the ship invisible or make it so the light would take slightly longer to go to the viewer due to some residual effects.

16. Originally Posted by Durakken
I forgot to mention that the energy to do it is also outside the realm of possibility, but anyways...

"Regardless if the crew claimed to have gone faster than light the relative observers would only see them to be travelling at "C" over each given distance."

I'm not sure you're disagreeing with what I said or not with this, but the reason the observer would see the path taken as only taking a day to go from A to B is because light is bounced from the ship from each position it was at during that day, even though it would be travelling faster, meaning that the light that bounced back would all reach the viewer during that day...

Of course this is just from practical knowledge...not math or GR. I don't know whether the light would be disrupted or not based on gravity generated...i would assuming travelling at that speed would create a lot and cause weird things to happen like you might see the bending of light from stars behind the ship and reflected light may reflect slower or faster off the hull...plus the time dilation may cause a small lag which could render the ship invisible or make it so the light would take slightly longer to go to the viewer due to some residual effects.
I think from a practical point of view some sort of warp drive where the spacetime around the spaceship is changed so that the apparent speed of the ship is greater than "C" while the ship remains below "C", Similar to a worm hole or like used by the Star Trekkers would make more sense, and at least be hypothetically possible.

I think you should stick along the lines of an/or extra dimensions with your ATM view on the subject. At least you can work along with current mainstream well proven theories, adding or modifying them as you go.

17. Originally Posted by Durakken
I forgot to mention that the energy to do it is also outside the realm of possibility, but anyways...

"Regardless if the crew claimed to have gone faster than light the relative observers would only see them to be travelling at "C" over each given distance."

I'm not sure you're disagreeing with what I said or not with this, but the reason the observer would see the path taken as only taking a day to go from A to B is because light is bounced from the ship from each position it was at during that day, even though it would be travelling faster, meaning that the light that bounced back would all reach the viewer during that day...

Of course this is just from practical knowledge...not math or GR. I don't know whether the light would be disrupted or not based on gravity generated...i would assuming travelling at that speed would create a lot and cause weird things to happen like you might see the bending of light from stars behind the ship and reflected light may reflect slower or faster off the hull...plus the time dilation may cause a small lag which could render the ship invisible or make it so the light would take slightly longer to go to the viewer due to some residual effects.
The main point i was making ,considering GR, regardless how much faster than "C" was claimed by the spaceship, the apparent speed recorded would be "C" from all reference points (except the onboard crew, they would record zero the instant they hit light-speed), any stationary relative observer would measure 2.5years time over 2.5ltys distance travelled for the round trip. The crew would measure zero time zero distance.

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Originally Posted by cosmocrazy
The main point i was making ,considering GR, regardless how much faster than "C" was claimed by the spaceship, the apparent speed recorded would be "C" from all reference points (except the onboard crew, they would record zero the instant they hit light-speed), any stationary relative observer would measure 2.5years time over 2.5ltys distance travelled for the round trip. The crew would measure zero time zero distance.

You know i just was gonna do this to show what i was talking about, but then just by looking at this it does show why it would be 2.5 instead of 1 like i had said...or at least closer to 2...but regardless i think it shows why any ship traveling like this would appear to be moving strangely...

http://durakkenstudios.com/relativelight.gif

stuff from point A and B i think would be like 1.5 LY away from the observer and C and D are 1ly away s you would get this really strange effect where the observer would see the ship at point A and B 1.5 years after the journey took place but the strange thing is that it would appear in the middle first and you would see it rush to both point A and B at the same time >.> and you would see that at roughly the same time you'd see it at point C rushing towards point B and months before that you'd see it between point C and D rushing towards both points...

so really at exactly 1 year after the journey took place you'd see the ship at 3 different places and slightly after that that you might see it at 4... but i don't know why someone would percieve it as taking 2.5 years...in fact from the outside observer just watching it seem to me the maximum length of time this journey would take place is 1.5 years, but maybe there is something i don't know about adding a year.

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Originally Posted by Confunded
This is very difficult for me to grasp. I would like to understand it though. Where can I read more? How did Einstein come up with something so counter-intuitive just by thinking about it?
This article discusses how Einstein worked out special relativity. Without meaning to detract from his achievement, he certainly wasn't working from a blank slate.

The fact that there are so many counter-intuitive concepts in science is an indication that we should never rely on our intuition.

20. Originally Posted by Durakken
You know i just was gonna do this to show what i was talking about, but then just by looking at this it does show why it would be 2.5 instead of 1 like i had said...or at least closer to 2...but regardless i think it shows why any ship travelling like this would appear to be moving strangely...

http://durakkenstudios.com/relativelight.gif

stuff from point A and B i think would be like 1.5 LY away from the observer and C and D are 1ly away s you would get this really strange effect where the observer would see the ship at point A and B 1.5 years after the journey took place but the strange thing is that it would appear in the middle first and you would see it rush to both point A and B at the same time >.> and you would see that at roughly the same time you'd see it at point C rushing towards point B and months before that you'd see it between point C and D rushing towards both points...

so really at exactly 1 year after the journey took place you'd see the ship at 3 different places and slightly after that that you might see it at 4... but i don't know why someone would perceive it as taking 2.5 years...in fact from the outside observer just watching it seem to me the maximum length of time this journey would take place is 1.5 years, but maybe there is something i don't know about adding a year.
looking at your drawing i can see how you came to your conclusions. But under GR if the observer measures the total distance travelled by the space ship to be a-b-c-d = 2.5ltys then if the ship is travelling at light-speed (which remember means zero time and distance for the crew on-board) then that observer would measure a time of 2.5yrs. The anomalies appear when the observer records a greater than "C" speed for the spaceship. But now with this notion you start to invoke causality effects. The ship apparently travels backward in time, or is in 2 different places at the same time relative to the observer

Causality effect is something you would need to consider when using more dimensions as well, but the main point for me is under GR if you reach speed "c" you travel nowhere but can be everywhere in no time. going any faster is undefined within our universe as we know it.

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Just figured out why you say to the viewer it would appear as 2.5ly...

If the viewer were to stand at one point and the ship were to move 2.5ly directly away at light speed then, yes, it would take 2.5years to make the journey, however that is not what I am saying is happening

The first leg of the trip is further away from the viewer than the second leg and also there is a point it comes closer. Further, the observer is directly perpendicular to the path the ship takes, all of which causes the effects of tri-position and later events being seen earlier.

Another thing I find interesting about this is that if another viewer were to watch on the exact opposite side, being 1.5 ly from the original viewer they'd see the same thing.

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