We know that the speed of light is always constant in space no matter the speed of the object emitting light, right?
Now consider this. An object is moving at half the speed of light and shined 2 beams of light; one in the direction it is moving and one in the opposite direction. If it was possible to see the beam of light, it would appear from the perspective of the object, that the beam of light moving in the same direction as its moving would appear to be moving at half the speed of light, and the beam of light opposite of the direction of the object would appear to be moving at 3/2 the speed of light.
Now, to apply this concept to something more possible. In theory, a device consisting of 3 laser beams, and 3 sensors could be able to calculate the absolute speed and direction it is moving in the universe. Say we made a device with 3 lasers set up so that they are all perpendicular to one another and sensors with known distances from the lasers, and all of this is occurring in a vacuum, then all at the same time the lasers would shoot at their respective sensors, and the times it took for the light to reach the sensors were recorded. The velocity of the lasers from the perspective of the device could then be calculated by using distance over time. Using the apparent velocity of the laser, the velocity of the object in the direction of the laser could be calculated by subtracting the apparent velocity from the speed of light. Then using these 3 velocity measurements, you could measure the speed that the device is moving through space itself. Using this device, it would be possible to measure the velocity of Earth at any point in time.
After researching the speed the Earth is moving, I saw that the method of figuring this out involves background radiation in the universe. Why would my method be discarded and the background radiation method be used instead. Surely I am not the first to think of this. Why would my method not be used?
Edit: I am aware that the speed of light is constant no matter what. Just it can seem to be going at 3/2 or 1/2 the speed of light from the perspective of something also in motion in the same way that a car going 60mph views a car going 90mph as going 30mph faster than it, or just 30mph in the perspective of the 60mph car.