# why does light not lose any speed? How does it stay consistent over millions and millions of light years?

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why does light not lose any speed? How does it stay consistent over millions and millions of light years?

In: Physics

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The closest analogy I can think of that would help at the 5 year old level is that this question is like asking why water is still wet after millions of years. Moving at the speed of light is just a natural part of light, even moreso than water being wet. Water can change to ice, and light can change wavelengths, but the light will still be moving at the same speed.

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It does lose speed, this is what gravitational lensing is. Light losing speed because of a gravitational effect. Also, it happens in prismatic effects and is the reason why we see varied colors during sunsets and sunrises.

Because it’s a fundamental property of light and a the universe itself. I know that’s not a satisfying answer, but that’s just the way it is. When we’re talking about fundamental aspects of the universe, at some point you can’t dig any deeper and you just have to understand that it’s how the universe works. Light always and only travels at the speed of light of whatever medium it’s in, or in a vacuum, at 299,792,458 m/s. It doesn’t matter if it’s been traveling for 1 second or 13 billion years.

– Light has no mass

– Things that have 0 mass move at the max speed in the universe. Makes sense right? When you push on things to move them mass provides resistance. So something with 0 mass moves at the max speed.

– There has to be a max speed. Otherwise laws of physics break down. That max speed happens to be 299,792,458 meters / sec in our universe.