Non-Relative Lightspeed

[Themorris]

Hi,

I've just read in my physics book, that the speed of light can't be seen relative to objects, so no matter from where I look at the light, it has lightspeed.

Now my question is:

Lets say if I emit some photons in a direction and move with half the speed of light into the opposite direction? Have the photons 1.5x times the speed of light?

greetings,

Themorris

[Ralathon]

Hi,

I've just read in my physics book, that the speed of light can't be seen relative to objects, so no matter from where I look at the light, it has lightspeed.

Now my question is:

Lets say if I emit some photons in a direction and move with half the speed of light into the opposite direction? Have the photons 1.5x times the speed of light?

greetings,

Themorris

Nope, they'll move at exactly the speed of light. The only thing that changes is the wavelength of the light, if you move towards the light it'll appear more blue and if you move away it'll seem more red.

If you have a train passing a station at half the speed of light and someone inside the train shines a flashlight forward both the guy on the train and the guy on the station see the light move at exactly the speed of light. This is thanks to time dilation, the guy in the train moves faster than the guy on the station and therefore time will move slower for him. This way he can measure the same speed of light without nasty paradoxes.

[Themorris]

Ok thank you!

I was really in thoughts about that...

[K^2]

If it boggles your mind, it should. If you want to understand why, then you need to understand that separation between any two events is constant in any coordinate system. That's no different from Galilean picture of the world, where distance between two objects is the same regardless of how fast you move past them. Except that in Relativity, separation includes time. So square of a separation s² = x² + y² + z² - c²t². Check for yourself that photon moving at the speed c connects two events with zero-separation. That means that from any coordinate system light appears to travel at the speed of light. On the other hand, if you consider distances and time separation separately, you'll notice that these change. That's length contraction and time dilation of relativity.

So entire Relativity is about the fact that space and time have to be considered together, as space-time. Once you do, all of it makes perfect sense.