# The Naked Scientists Forum

### Author Topic: ?lights travelling in opposite directions= c2?  (Read 2909 times)

#### CZARCAR

• Hero Member
• Posts: 686
##### ?lights travelling in opposite directions= c2?
« on: 21/01/2010 22:52:08 »
1 futon goes in 1 direction & the other goes the opposite so relative to each other its possible to exceed 186000mi/sec.? then what happens?
futon= twins need a seat for the ride...eventually

#### LeeE

• Neilep Level Member
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##### ?lights travelling in opposite directions= c2?
« Reply #1 on: 22/01/2010 01:06:32 »
You can only measure the relative speed of one futon to the other if you're on the other futon; if you measure the speeds from a third point that is stationary relative to both futons you'll find that they are both travelling at 'c'.  Regardless if which futon you're on, you'll also measure the speed of the other futon as 'c'; time dilation and length contraction make it all work out to give the same answers.

Why futons, and not just chairs or sofas?

#### CZARCAR

• Hero Member
• Posts: 686
##### ?lights travelling in opposite directions= c2?
« Reply #2 on: 22/01/2010 11:59:06 »
You can only measure the relative speed of one futon to the other if you're on the other futon; if you measure the speeds from a third point that is stationary relative to both futons you'll find that they are both travelling at 'c'.  Regardless if which futon you're on, you'll also measure the speed of the other futon as 'c'; time dilation and length contraction make it all work out to give the same answers.

Why futons, and not just chairs or sofas?
i meant photons-fotons & futons are vain humor'
if 2 objects travel in the same direction & a is going twice the speed of b , a would be accelerating away from b? so i figure if 2 photons emerge from a star in opposite directions then their relative speeds would result as c2? & the result would be e=mc2 [where m=star]

#### litespeed

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##### ?lights travelling in opposite directions= c2?
« Reply #3 on: 22/01/2010 21:47:11 »
CZ

Relatively speaking, all photons appear to be traveling at c to all observers from all locations at all times [in a vacuum]. This includes observers in a sub-c star ship who might be chasing one or the other of two photons traveling in opposite directions. After that, lots of complicated things seem to happen.

#### JP

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##### ?lights travelling in opposite directions= c2?
« Reply #4 on: 23/01/2010 04:22:56 »
Special relativity just says that no object can appear to move faster than the speed of light.  The space between the two photons isn't an object, so it can appear to grow at 372,000 mi/s.  Each photon will only appear to move at 186,000 mi/s.

#### Geezer

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• "Vive la résistance!"
##### ?lights travelling in opposite directions= c2?
« Reply #5 on: 23/01/2010 06:08:16 »
You know, a futon that can travel at the speed of light might be really handy if you have an unwanted guest.

Do you think the LHC might actually discover futons?

(Sorry for the interruption!)

#### Farsight

• Sr. Member
• Posts: 396
##### ?lights travelling in opposite directions= c2?
« Reply #6 on: 23/01/2010 11:44:28 »
CZ: the futons really are moving apart at 2c. After one year they're two light years apart, after two years they're four light years apart, and so on. But if you were sitting on one looking at me sitting on the other, then like Lee, litespeed, and jp said, you'd see me receding at c, not 2c. Check out the velocity addition formula at http://en.wikipedia.org/wiki/Velocity-addition_formula.

#### The Naked Scientists Forum

##### ?lights travelling in opposite directions= c2?
« Reply #6 on: 23/01/2010 11:44:28 »