# B Speed of light, rapidity of light and Cantor's infinities

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1. Jul 23, 2015

### AlexDB9

The natural expression of speed in relativity (and thus the true meaning of speed) is through the concept of rapidity, which comes from incorporating the gamma factor. It turns out that the rapidity of light is infinite. So the question of whether there can be speeds greater than light becomes the question of whether there can be rapidities greater than infinity.

Here comes Cantor, who as you may know, proved one of the most surprising results in all of mathematics. He proved that there are different sizes of infinities and, on top of that, that there is no "largest" infinity. The last part also clears the waters as to what kind of rapidity is the rapidity of light. Is it the infinity of integers or of real numbers (which is a larger infinity)? It doesn't matter, because there is no largest infinity. So, Cantor's result gives a little hope that, at least mathematically, the infinite rapidity of light is not a limit.

What are your thoughts on this?

2. Jul 23, 2015

### phinds

I think you are applying math to reality in a way that does not compute.

3. Jul 23, 2015

### AlexDB9

4. Jul 23, 2015

### phinds

You are positing a personal theory that the "speed of light", which is the name we give to the "universal speed limit" may not BE the universal speed limit because of some abstract math thing. I don't think that has any basis in reality, it's just a math thing.

5. Jul 23, 2015

### Staff: Mentor

No, this is not correct. What is correct is that the rapidity of light is undefined. The various concepts of infinity in mathematics have nothing to do with the behavior of light in relativity.