Need some help with maths

[Silent_Buddha]

Absolutely correct from the perspective of either object! To either one of them, the other object is in every way approaching at 80% of the speed of light.

But let's think of the implied external observer who measures one object moving north at 50% of the speed of light and the other object on a collision course moving south at 50% the speed of light. What's the closure speed? In this case, the simple linear speed addition is CORRECT and you can say that the objects are approaching each other at the speed of light. It would even be correct if each one was moving at 90% of the speed of light, and you would properly say they were approaching each other at 180% of the speed of light. You're using a speed to measure a seperation distance which is decreasing over time at a rate of 1.8 c. There's no paradox: no object or information is moving faster than light.

So what you're saying is...

It's all relative? /nudge /nudge (there needs to be a nudge emote)

Regards,
SB

 

[Alexko]

Which part? If it's nutball's suggestion, it works as follows:

If both entities are moving at half of the speed of light, you would expect them to be moving towards each other at the speed of light.

This means that two objects, each travelling at half of the speed of light, end up moving towards each other at 80% of the speed of light.

That's a really nice example. Also, yay for MS Paint maths!

 

[spworley]

So what you're saying is...
It's all relative? /nudge /nudge (there needs to be a nudge emote)

A student recognizes Einstein in a train and asks: Excuse me, professor, but does New York stop at this train?