Is the speed of light constant in a vacuum?

AI Thread Summary
The discussion centers on the nature of vacuum in space, questioning whether the term "hard vacuum" is appropriate given the presence of low-density particles, plasma, and electromagnetic fields. It is clarified that while space contains these elements, their impact on light propagation is negligible due to their extremely low density. Electromagnetic fields do not significantly affect light according to classical theories. However, virtual particles do interact with light, albeit weakly, affecting the linearity of magnetic fields. Overall, the speed of light remains effectively constant in a vacuum despite these interactions.
Thomas1989
Messages
14
Reaction score
1
Hello everyone!

Just something I was thinking about today that I haven't been able to shake. I recently read that space is not actually a perfect vacuum, but that it contains low density particles, plasma, electromagnetic fields and so on. Is 'hard vacuum' the correct definition, or is it okay just to use vacuum?

I'd like to know why these low density particles, fields, and plasma don't interact with the light or slow it down in any way (or do they?) While I'm on the subject of particles, do virtual particles exist in space, and do they interact with light?

Thanks!
 
Astronomy news on Phys.org
Thomas1989 said:
Hello everyone!

Just something I was thinking about today that I haven't been able to shake. I recently read that space is not actually a perfect vacuum, but that it contains low density particles, plasma, electromagnetic fields and so on. Is 'hard vacuum' the correct definition, or is it okay just to use vacuum?

The vacuum, as defined, contains no particles or plasma. Electromagnetic fields are classically unimportant, since Maxwell's theory is linear and one electromagnetic field does not affect the propagation of another.

It's true that even the space between galaxies/clusters/etc. is filled with an extremely tenuous gas. However, the density in these regions is so low that the effect on the propagation of light is (mostly) negligible.
I'd like to know why these low density particles, fields, and plasma don't interact with the light or slow it down in any way (or do they?) While I'm on the subject of particles, do virtual particles exist in space, and do they interact with light?

Thanks!

Virtual particles do interact with light. In particular, they destroy the linearity of magnetic fields and mean that light does interact with other light, albeit very weekly. This effect, however, is much too small to be seen in astrophysical experiments and can only be seen in very precise particle colliders.
 
Is a homemade radio telescope realistic? There seems to be a confluence of multiple technologies that makes the situation better than when I was a wee lad: software-defined radio (SDR), the easy availability of satellite dishes, surveillance drives, and fast CPUs. Let's take a step back - it is trivial to see the sun in radio. An old analog TV, a set of "rabbit ears" antenna, and you're good to go. Point the antenna at the sun (i.e. the ears are perpendicular to it) and there is...
This thread is dedicated to the beauty and awesomeness of our Universe. If you feel like it, please share video clips and photos (or nice animations) of space and objects in space in this thread. Your posts, clips and photos may by all means include scientific information; that does not make it less beautiful to me (n.b. the posts must of course comply with the PF guidelines, i.e. regarding science, only mainstream science is allowed, fringe/pseudoscience is not allowed). n.b. I start this...

Similar threads

Back
Top