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Author Topic: Headlights on my spaceship?  (Read 7612 times)

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Offline swashy

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Headlights on my spaceship?
« on: 13:49:34, 15 January, 2011 »
Am i right in thinking that no matter how fast I mangage to to propell myself across space in my ship, my headlights will always light the way?   :nerd:
Ade

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Offline Kellys_eye

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Re: Headlights on my spaceship?
« Reply #1 on: 14:13:23, 15 January, 2011 »
With todays fuel prices?  I don't think so.
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Offline andrew s

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Re: Headlights on my spaceship?
« Reply #2 on: 15:41:55, 15 January, 2011 »
Yes the speed of light is a constant for all inertial observers and so you will see your headlight moving away from a speed c as will your tail and side lights. Andrew

Offline Nomis Elfactem

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Re: Headlights on my spaceship?
« Reply #3 on: 15:49:23, 15 January, 2011 »
Have you been drinking at lunchtime again Ade ?
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Offline swashy

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Re: Headlights on my spaceship?
« Reply #4 on: 17:23:14, 15 January, 2011 »
No, no drinking, just idle curiosity  

So any photon that was traveling along with me at c, which say, came from the same sourse as myself, such as a flashing beacon on my launch tower, would witness my headlight emitted photons traveling at 2xc relative to my starting point ?   :duh:

Perhaps I need that drink afterall
Ade

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Offline Somelier

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Re: Headlights on my spaceship?
« Reply #5 on: 18:48:49, 15 January, 2011 »
I look at it this way - if an arrow leaves my archery bow at 80 kph when I'm standing still, then if I'm moving forward at 20 kph, then the arrow will leave the bow at 100 kph relative to the ground. If I'm travelling at the speed of light, then surely the light from my headlights would travel at twice the speed of light relative to a stationary object. Am I right? Will we have to wait until we meet Spock before we get a definitive answer? Am I going daft? Please do not answer that last question (I already know the answer!)
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Offline swashy

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Re: Headlights on my spaceship?
« Reply #6 on: 18:57:22, 15 January, 2011 »
My thoughts exactly, nothing can travel faster than c, unless you are already at a velocity before you begin, which would mean that we could have photons all traveling at c, yet overtaking each other on journeys which had different origins of velocity

 :crazy:
Ade

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Online koootzz

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Re: Headlights on my spaceship?
« Reply #7 on: 19:28:54, 15 January, 2011 »
Slightly different take on it but as space is a (near) vacuum there wouldn't be anything for the light to reflect off so you wouldn't see the light, however an observer in front of you would be able to.

The speed side of it is covered by Special Theory of which I understand very little except it has something to do with time dilation and space contraction. :confused:
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Offline Charles

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Re: Headlights on my spaceship?
« Reply #8 on: 20:21:24, 15 January, 2011 »
The answer to the conundrum (according to special relativity) is that speeds do not simply add like 2+2=4.  So travelling on the spaceship, the light leaves you at the speed of light.  Another observer would still see the light moving at the speed of light, no matter how fast the spaceship was going relative to the observer.
See wikipedia for more detail
http://en.wikipedia.org/wiki/Velocity-addition_formula


Offline andrew s

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Re: Headlights on my spaceship?
« Reply #9 on: 21:22:38, 15 January, 2011 »
Charles is correct. While it may not seem right it explains a number of measurable effects that otherwise seem very strange - e.g. contraction & time dilation. In fact without making correction for the results of both special and general relativity GPS technology just would not work. Andrew

Offline swashy

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Re: Headlights on my spaceship?
« Reply #10 on: 23:22:59, 20 January, 2011 »
Yep, it's that space time dilation thing that is giving me some headscrathing moments

Just been reading that, if I was travelling in my spaceship at 99.99999999 (8 decimal places) % of the speed of light, then a trip to M31 which is approx 300 Mly away, would in fact only take me 50 years to get there because of the dilation of the space/time!  I find this fact quite remarkable, and gives me hope for the future of mankind, of course the fact also remains that on earth, 300 million years would have passed during my journey, so lets hope I remembered to lock the front door!

The point I am trying to get to, though, is, would the beings on the planet I am heading for in M31, be able to see me (my headlights) coming at at just a few moments after I left?  think about it
Ade

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Offline Charles

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Re: Headlights on my spaceship?
« Reply #11 on: 11:35:53, 21 January, 2011 »
I think that the beings on the planet would see your headlights only a very short time before you crashed into them, because as far as they are concerned, the light from your headlights approaches them at the speed of light, and you approach them at 99.99... % of the speed of light.

Offline Dave Dubya

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Re: Headlights on my spaceship?
« Reply #12 on: 20:17:38, 21 January, 2011 »
From memory of a past discussion on this:

- the person in the lightspeed car would see their headlights as usual
- anyone viewing the lightspeed car would not see the lights on

Offline andrew s

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Re: Headlights on my spaceship?
« Reply #13 on: 22:52:58, 21 January, 2011 »
The basic principle of special relativity is that any (intertial) observer always sees light leave its source and the same speed c.  It is from this basic fact that Einstein derived the formulas for time dilation & length contraction etc.

Offline Scotty H

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Re: Headlights on my spaceship?
« Reply #14 on: 03:06:00, 26 February, 2011 »
I think that the beings on the planet would see your headlights only a very short time before you crashed into them, because as far as they are concerned, the light from your headlights approaches them at the speed of light, and you approach them at 99.99... % of the speed of light.
Yet they have seen this light coming from many millions of years ago!!!!! and then you smack into them. Explain that one to the insurance
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