Starship Asterisk*

Do galaxies every just break apart and stop rotation?

John128 wrote:Do galaxies every just break apart and stop rotation?

Galaxies can be torn apart by interaction or collision with other galaxies, but for them to just break apart or stop on their own I don't think would be possible.

http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... g+galaxies
http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... +collision

John128 wrote:Do galaxies every just break apart and stop rotation?

On any reasonable time scale we can deal with, galaxies are stable structures. They may be disrupted by a collision with another galaxy, but the resulting structure or structures eventually reconsolidate.

Largely due to the conservation of angular momentum, rotation is the normal state of pretty much every object in the Universe. Objects do not, as a rule, ever stop rotating.

Chris Peterson wrote:Largely due to the conservation of angular momentum, rotation is the normal state of pretty much every object in the Universe. Objects do not, as a rule, ever stop rotating.

It is fascinating to contimplate this... everything constantly moving... for a long time we thought the Earth was rock steady and everything else moved. Now we know better.

Nothing is at a static state... and only 'nothing'. So how fast are we 'really' moving? (Relative to the Universe) Do we measure speed of travel at a fixed reference to Earth's relationship to the Sun... like planetary mass and weight? Or is there another factor in relating to other cosmic objects?

emc wrote:It is fascinating to contimplate this... everything constantly moving... for a long time we thought the Earth was rock steady and everything else moved. Now we know better.

Nothing is at a static state... and only 'nothing'. So how fast are we 'really' moving? (Relative to the Universe) Do we measure speed of travel at a fixed reference to Earth's relationship to the Sun... like planetary mass and weight? Or is there another factor in relating to other cosmic objects?

Inertial motion "relative to the Universe" may be a meaningless concept, as there's no assurance that the Universe provides a fixed frame of reference. Indeed, most cosmological theories place every observer at the center of the Universe, so there can be no motion with respect to the Universe, only with respect to other objects in the Universe. We can (in principle) determine our inertial motion with respect to the observable Universe by measuring redshifts. And we might (in principle) determine our non-inertial motion (which is, in some sense, with respect to the Universe) by measuring anomalous accelerations.

Thanks for the reply Chris Peterson,

I should have thought more carefully before posting... when I wrote 'Relative to the Universe' I was thinking of other cosmic objects.

I see from your answer that we must have a baseline, so each of us becomes that... Cool! So we're kinda still "rock steady" so to speak.

emc wrote:Nothing is at a static state... and only 'nothing'. So how fast are we 'really' moving? (Relative to the Universe) Do we measure speed of travel at a fixed reference to Earth's relationship to the Sun... like planetary mass and weight? Or is there another factor in relating to other cosmic objects?

An earthbound observer rides along with the Earth's spin, the Earth's orbit around the Sun, the Sun's galactic orbit, the Galaxy's motion in the local group, and so on. The Monty Python Galaxy song summarizes it nicely (starting 25 seconds in): http://www.youtube.com/watch?v=rgCZjSBTtyY

The cosmic microwave background (CMB), the farthest surface in the Universe that we can see right now, provides a great inertial reference frame against which we can measure our speed "relative to the Universe." From Earth, the CMB shows a dipole anisotropy (APOD link): opposite sides of the microwave sky are red- and blue-shifted, and it turns out that we're moving at 600 km/s toward the Virgo supercluster. Okay, 600 km/s is very fast, but the accelerations we feel from all these motions are minuscule, making even the Earth's surface a pretty good inertial (non-accelerating) reference frame.

Thanks for your response Pete,

I enjoyed the Monty Python skit. And I followed your link to another APOD and finally the Great Attractor. Kind of an information trek similar to our shared cosmic journey riding along on planet Earth.

The Great Attractor, being a mystery, I hope allows some imaginative speculation on my part... I wonder... that if the unknown GA mass is truly Dark Matter then where does it come from? And why is it located where we are headed? I speculated Black Hole emissions in another Asterisk thread. I was joking of course, but there is some imagined logic... Black Hole Emissions transcending time and space... but there has to be some physical medium for matter to move from one place to another, right?... so my imagination, perhaps, is just being imaginative...

Is there another possibility that our motion is just our trajectory based from the Big Bang... and there is no GA? This is not likely based on what I read in Wiki on Dark Matterand I realize I am missing the education required to understand the cosmos, but it is fun to try.

I know little of what I speak... I haven't quite wrapped my head around the cosmos.