space ponderings

[kevina]

Hi there I was checking out a thread about us crashing into andromida galaxy simply browseing and noticed the thread was hijacked and turned into a argument of kinds. For those who don't know me I'm new to the forums and am currently working on my undergraduate.

 

Anyhow basicly someone pointed out that dark energy was responsible for speeding the galaxy up which sounded like gravity.

 

Anyhow if photons don't have mass how could they be speed up ?

 

I thought albert einstien gave the speed of light while traveling through a vacum a fixed number and to me the edge of our galaxy would be vacume.

 

Anyhow its just me pondering I've probably got it all wrong

[Spyman]

There are two very different concepts that happen to be named very similar and cause a lot of confusion, they are called dark matter and dark energy:

 

Dark matter represents the problem that stars inside galaxies orbit the center at higher speeds than they should be able to, unless there is a large amount of unseen mass increasing the force from normal gravity and helping them hold on to their stars at higher orbital velocities.

 

Dark energy represents the observation that the universe on large scales, between clusters of galaxies, seems to be expanding at an accelerated rate, gravity should counter and slow down this rate, but measurements of redshifts from very distant supernovas reveals that the expansion is speeding up.

 

As such the Milky Way and Andromeda galaxy are not "speeding up", although they are on collision course and will likely merge in the future.

(The interaction of their mutual gravity are of course causing them to accelerate towards each other, but that is no "dark" mystery.)

 

 

Photons don't speed up, they always travel at the speed of light through space. But photons carry energy which according to relativity also interacts with gravity, they both bend spacetime and follow the curved path of spacetime, just like ordinary matter.

 

 

There is no true vacuum anywhere in the universe, there are tiny amounts of matter spread out sparsely everywhere and a large amounts of photons crossing all volumes of space, even if we would shield off a part of space it would still contain the zero point field with its fleeting particles popping in and out of existence. (In the context of lightspeed, you are correct that photons are not noticeably affected and travel freely.)

 

 

Asking questions here or in other parts of this forum, is a very good way to increase your knowledge on whatever interests you at the moment.

[kevina]

Ah thanks for clearing that up. Believe either I might have mis understood the original post or there was some bad language which caused me to miss what they were saying. Anyhow thank you for a clarification I love stuff stuff like this and usually check out everything I don't quite get on Wikipedia and reading various science thread.

 

 

Thanks again for the reply