Why does the speed of light vary in different mediums even if light does not need a medium to travel?

I think you are confused between the two statements. The fact that light does not need a medium to travel is irrelevant of its speed. The reason why Light does not need any medium to travel is because it is an electromagnetic wave. As far as we know, any wave changes its speed in a different medium, be it mechanical or electromagnetic. Also, I think you are being a bit biased towards the properties of light. I mean, if any electromagnetic wave travels in some medium its wavelength and velocity are not only dependent on its own properties but also the medium's properties(Refractive index). Electromagnetic wave interacts with the matter in the medium. According to Maxwell, the velocity of an electromagnetic wave is given by:- [math]\mu\mu_0\varepsilon\varepsilon_0=1/v^2[/math] where [math]\mu\varepsilon[/math] are properties of the medium. Since they are absent in vacuum, we have [math]\mu\varepsilon =1[/math]. Now, if light is in no medium, it still has a speed which means it is moving thereby conforming that light needs no medium to travel. Hence, the formula proves that light changes its speed in any medium without contradicting the statement that "light does not need a medium to travel".

What would make life not worth living?

Life is not worth living when we are always living in fear for the things which has not yet happened or may which will never ever happen.Now a days, we compare ourselves with everyone without knowing that is it worth to compare or not. Due

Why are insects attracted to carnivorous plants?

You're in good company, Charles Darwin raised a similar question 140 years ago, one of his particular interests was Dionaea muscipula, a Venus flytrap species. Darwin expanded his studies from sundews and flytraps to other species, eventually recording his observations and experiments in 1875 in a book, Insectivorous Plants.Among the estimated quarter of a million vascular plants