We measure space objects speed in relation to earth. But since earth is also moving through space, how do we know the true speed of objects without a universal “non moving” point?

Question

The speed of an object is measure relative to the observer. But since all objects are moving in relation to all objects, how can we know the true speeds of things? Wouldnt two observers on different planets measuring an object in space come up with different answers?

In: Physics

Answer 1

Why does there need to be a “true speed”? And yes, two observers in different planets would measure the same event differently. The key though is that they can both go through something called a Lorentz Transformation, and get the answer that the other would have. There is no true 0 speed, the same way there is no true 0 longitude. In both cases all coordinate systems are valid.