How Can Galaxies Travel Faster Than Light?

Thu Mar 29, 2012 1:05 am » by **Evildweeb**

by tdarnell on Dec 14, 2010

Get Astronomy tweets here http://twitter.com/DeepAstronomy

Probably my biggest regret when I made the Hubble Deep Field in 3D video is saying the phrase "these galaxies are racing away from us, in some cases faster than light".

I had originally thought I was being clever and the comment would spur discussion. instead there was no discussion, only name calling and I mightily regretted putting it in there.

Anyway, this video was a long time coming, I had been meaning to make this for some time to illustrate what I was talking about.

Music used:

http://www.archive.org/details/kpu107

Don't forget to play with WolframAlpha, it's awesome!:

http://www.wolframalpha.com/

http://www.youtube.com/watch?v=myjaVI7_6Is

:nails:

Thu Mar 29, 2012 1:23 am » by **Noentry**

That was very informative.

:cheers:

Thu Mar 29, 2012 1:44 am » by **Evildweeb**

noentry wrote:That was very informative.

Thanx noentry, it woulda been up here yesterday had it not been for, well, you know who.

LOL

cheers

:cheers:

Thu Mar 29, 2012 1:56 am » by **Audreyrose**

Oh, you were doing very well up until the 3 minute mark!

I was very impressed!

But, here's your error. The 3 different "types" of redshift, only refers
to the 3 different circumstances which cause light from stars, galaxies,
and the cosmic microwave background to be shifted.

The formula that relates the "z" value to the speed "v" at which the object
is moving away from us is the same for whether it's a local galaxy, undergoing
motion due to local gravitational effects (like as you pointed out, the Andromeda
galaxy is moving TOWARDS us, due to it's gravitational attraction to our Milky
Way galaxy), or if its motion is due to the fact that the universe is expanding
(cosmological redshift).

So go back to that wikipedia page: the top box gives the relativistic doppler
shift formula for Minkowski spacetime (flat spacetime, which the universe more
or less is), and use the formula for motion in a purely radial direction (as the
cosmological redshift is due to galaxies moving directly away from us).

In this formula, if the galaxies speed "v" was equal to the speed of light "c",
the "z" value is: z=infinity!

So any "z" value less than infinity means the galaxy is moving at less than
the speed of light.

I studied astronomy at Caltech and worked on these types of galaxies, that is
how I know this.

P.S. The formula is at this wikipedia page:

http://en.wikipedia.org/wiki/Redshift

Thu Mar 29, 2012 1:58 am » by **Ghost32**

I dont think that the video above is accurate.

The birth and the death of the photon is the same instance but space time is warped and we percieve it as travelling, but thats just an effect of the human mind, and if something was really traveling at that speed it would not actually move because at the speed of light, time and space stand still.

Also that what we think is a constant is not really, The speed of light and time and the expansion of the universe all seem to be speeding up. :think:

Excerpt From The Primacy Of Conciousness

:ghost:

32

Thu Mar 29, 2012 2:00 am » by **Evildweeb**

audreyrose wrote:Oh, you were doing very well up until the 3 minute mark!

I was very impressed!

But, here's your error. The 3 different "types" of redshift, only refers
to the 3 different circumstances which cause light from stars, galaxies,
and the cosmic microwave background to be shifted.

The formula that relates the "z" value to the speed "v" at which the object
is moving away from us is the same for whether it's a local galaxy, undergoing
motion due to local gravitational effects (like as you pointed out, the Andromeda
galaxy is moving TOWARDS us, due to it's gravitational attraction to our Milky
Way galaxy), or if its motion is due to the fact that the universe is expanding
(cosmological redshift).

So go back to that wikipedia page: the top box gives the relativistic doppler
shift formula for Minkowski spacetime (flat spacetime, which the universe more
or less is), and use the formula for motion in a purely radial direction (as the
cosmological redshift is due to galaxies moving directly away from us).

In this formula, if the galaxies speed "v" was equal to the speed of light "c",
the "z" value is: z=infinity!

So any "z" value less than infinity means the galaxy is moving at less than
the speed of light.

I studied astronomy at Caltech and worked on these types of galaxies, that is
how I know this.

Outstanding response Audrey, and welcome btw.

There has been serious commentary regarding the issue with Andromeda approaching us also having a shift differential that makes no sense, according to this model.

I would be interrested in hearing your take on both the Andromeda data as well as how it relates to the supposed examples of outward motion shift.

Thanx again.

cheers

:cheers:

Thu Mar 29, 2012 2:19 am » by **Audreyrose**

You're welcome!

I truly meant to write a respectful, but helpful, reply and
am so glad you took it that way! The narration was beautiful -
is that your voice? Great graphics too.

I don't know that much about Andromeda, only that it is moving
towards us (in our Local Group, there are two big galaxies,
the Milky Way and Andromeda, and a bunch of smaller ones,
maybe 20 (don't remember exactly) teeny tiny ones in comparison).

So, all that I know is that because of gravity, the two big galaxies
are indeed moving towards each other, and in fact will collide in
some 3 billion years or so (so stock up on your emergency supplies
soon!).

But that's all I know, so I can't help you with any details beyond that.

Those high "z" galaxies I actually did a lot of research on, so that's
why I felt so confident in my reply regarding "z" values.

P.S. This may help a little with your question though. Because
the Andromeda galaxy is so close to us, any effects due to the
expansion of the universe will be extremely minimal, and in fact
can probably be ignored.

Thu May 03, 2012 7:55 pm » by **Audreyrose**

Hi,

I can help answer any more galaxy or science questions if anyone has any.

I have been writing on this board for a while, and decided I really wanted to let
the forum members here know who I am.

So, see my bio at http://melindajanekellogg.com

I am currently unemployed, so would be happy to answer
questions whlie I am here, if you are interesting in having a real "professor"
to talk to!

I was a great teacher, so I will be really nice and respectful - there are NO
stupid questions!

Thanks,
Audrey