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Author Topic: If i'm reversing at the speed of light, and turn on my headlights, what would an observer see?  (Read 6419 times)

Mark Gallagher

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Mark Gallagher asked the Naked Scientists:

I am an independent observer (a disembodied entity of myself); I am watching myself in my car in space. My car, in reverse gear, can travel the speed of light. I select reverse gear and accelerate to the speed of light. I switch on my headlights. What do I see, as the observer?


What do you think?


 

lyner

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Light speed travel does not really fit with any theory with which I could give you and answer.
All I can say is that, from a photon's point of view (and they do go at c), time would not be progressing  - its clock is permanently stopped - so it would have no concept of speed.
 

Offline lightarrow

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Mark Gallagher asked the Naked Scientists:

I am an independent observer (a disembodied entity of myself); I am watching myself in my car in space. My car, in reverse gear, can travel the speed of light. I select reverse gear and accelerate to the speed of light. I switch on my headlights. What do I see, as the observer?


What do you think?

An infinitely bright flash of light of infinite frequency (and so you obviously would die, if the total energy emitted is enough).
« Last Edit: 06/05/2008 15:04:21 by lightarrow »
 

Offline LeeE

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What you would see is your headlights red-shifted and growing dimmer as their apparent wavelength increased due to your local acceleration and time dilation.  When you reach the speed of light, your time rate will have become zero, at which point the wavelength of the light emitted from your headlights will become infinite and therefore have zero energy.

Actually, accelerating your car up to the speed of light is probably not a good idea, let alone doing it in reverse without some good stunt car driving tution first.  At the speed of light, as well as your local time rate becoming zero, your mass and density would become infinite so you'd probably turn into a black-hole.

<Edited to add missing 'the wavelength of' to the last sentence of the first paragraph - oops>
« Last Edit: 07/05/2008 15:06:54 by LeeE »
 

lyner

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You would 'see' nothing - as time would be standing still, em waves would have NO FREQUENCY!
This is the equivalent sort of question to my Grandfather's old chestnut "What happens when an irresistable force meets and immoveable object?" It is a non-real scenario so you get daft answers.
 

Offline turnipsock

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I'm thinking that reversing at the speed of light is very silly, people won't see you coming and will rear end you.

Is there something in my insurance about people reversing into me at the speed of light? I will check next time.
 

Offline lightarrow

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You would 'see' nothing - as time would be standing still, em waves would have NO FREQUENCY!
This is the equivalent sort of question to my Grandfather's old chestnut "What happens when an irresistable force meets and immoveable object?" It is a non-real scenario so you get daft answers.
Ah yes, I understood the problem in the opposite way.
 

lyner

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This 'being a photon' idea seems to be a common thread which runs through a lot of threads.??
The odd thing about the photon's perceived time makes the idea of instant communication / quantum entanglement etc sound less and less unreasonable and more understandable.
 

Offline TheHerbaholic

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This has actually got me thinking. I mean if your looking at somebody reversing away from you at the speed of light, could they still see you? I know they would not be in seeing distance for long, but if you was to sit in a car, reverse faster than the speed of light,lets just say you survived and the car did and you drive past somebody, you actually wouldn't be able to see them when they are 2ft in front of the car. Because the light that bounces off them, wouldn't catch up with the car because your already going faster than the speed of light.

So if your going the speed of light backwards, and was to switch on the headlights you wouldn't see your headlights, because the light would never be able 2 cover the car because your going faster than the light is.

But then if you waved your hand infront of your face would you see that?
Becuase the light bouncing off your hand would never be able 2 reach your eyes because your head is moving at the speed of light.
Then again, if it was inside the car wouldn't their be an effect like if your driving down the motorway, open the window and put your arm on the side of the car? Like you feel the wind blowing over the side of your arm but theirs no wind inside the car.

Now along them same lines would you have some kind of effect like this if you turned on a light, inside a car moving at the speed of light, then the light wouldn't be slown down by the outside of the car moving and move faster than the speed of light?
Like if your on a plane going 500mph, and ran forward down it, you wouldn't be running at 500mph, but you would be traveling it. Maybe the same could happen with light?
Becuase after all it's only faster speeds, well alot faster lol but wouldn't the same principle apply?
 

lyner

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TH
When you are dealing with Relativity you cannot just add and subtract speeds as you would in 'aeroplane and train' calculations. You have to acknowledge that life changes once you start going fast (or even very slowly, if you want to be pedantic).
If you want to get an understanding of these things you should start with the ideas of Special Relativity - light speed is always measured to be the same, whatever you are doing and wherever you are - all motion is relative in inertial frames. The consequences are that time, mass and distance become  'distorted' and there are several apparent paradoxes. But they aren't really paradoxes when you look at the bigger picture.
Just leap into Google and read what some of the .edu sites have to say. There are a number of '.b*****ks' sites which you will have to spot and avoid or you may end up more confused.
This is not just a five minute exercise!
 

Offline ukmicky

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    • http://www.space-talk.com/
 

Offline TheHerbaholic

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That site is, really interesting. Thanks alot uk micky!
The Mass = Energy part especialy. But I'm now so confused to how light would actually travel the same in the train to outside it. lol The next time my old science teacher walks into the boozer I'll have a chat with him about it lol
 

Offline qazibasit

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you will see nothing  because before the light strikes the next object and comes back to you, you will move forwards and far away so there will still be darkness.
 

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