Thread: Dark Matter

Originally Posted by hoglahoo

Craig,

As far as I can tell, matter can change location relative to each other at a faster pace than the expansion of the universe. Just a few minutes ago I noticed that a chocolate chip cookie grew closer and closer in proximity with my maw until it actually became part of me. Empirical evidence that universal expansion does not prohibit collisions!

Aha! But my dear colleague...after said chocolate chip cookie entered your maw, was masticated, and swallowed, it has now begun the process of continuing to expand your midsection.

Thus, the universal expansion continues unabated!

I don't get what you all are going back and forth for. If leading scientists in various fields of physics and astronomy have reason to believe that dark matter exists, than I'd say chances are they have pretty good reasons to say so. If you don't believe them, you should go and look at their research, not debate about it on here. Maybe some members know enough to make a compelling, "scientific" argument, and maybe not, but just because someone here cannot does not mean that no one can.

I put "scientific" in quotes, because in a thread I made, it seemed most members were not able to adequately define what science is.

I've tried to chime in in a few other threads, and I've tried to start a thought provoking thread, and I have come to the conclusion that I'm finished with it on here. There is too much "popular science," most of which I would say is not actually science, and not enough people who are willing to look at real scientific papers (or even wikipedia), so what's the point. If you really want to know something, do some real research.

That is my 2 cents based on my current outlook. But things always change...

Here's an answer from Karen Masters on the same question:

Anyway it's quite natural for galaxies to collide even though the universe is expanding - although I could see why you might get confused about it. What happens is that there is a battle between the forces of gravity between the two galaxies (which is trying to pull them together) and the expansion of the universe (which is trying to pull them apart). With galaxies that start out quite close together, it is almost always gravity that wins, so in the end the galaxies will collide. This will most likely happen to the Milky Way and the Andromeda galaxy (our nearest large neighbour) in a few billion years.

Originally Posted by holli4pirating

I don't get what you all are going back and forth for. If leading scientists in various fields of physics and astronomy have reason to believe that dark matter exists, than I'd say chances are they have pretty good reasons to say so. If you don't believe them, you should go and look at their research, not debate about it on here. Maybe some members know enough to make a compelling, "scientific" argument, and maybe not, but just because someone here cannot does not mean that no one can.

I put "scientific" in quotes, because in a thread I made, it seemed most members were not able to adequately define what science is.

I've tried to chime in in a few other threads, and I've tried to start a thought provoking thread, and I have come to the conclusion that I'm finished with it on here. There is too much "popular science," most of which I would say is not actually science, and not enough people who are willing to look at real scientific papers (or even wikipedia), so what's the point. If you really want to know something, do some real research.

That is my 2 cents based on my current outlook. But things always change...

Whoah now!

If leading scientists in various fields of physics and astronomy have reason to believe that dark matter exists, than I'd say chances are they have pretty good reasons to say so.

What ever happened to peer review? Subjecting hypothesis to scrutiny and discourse?

Originally Posted by NYCshaver

Here's an answer from Karen Masters on the same question:

Anyway it's quite natural for galaxies to collide even though the universe is expanding - although I could see why you might get confused about it. What happens is that there is a battle between the forces of gravity between the two galaxies (which is trying to pull them together) and the expansion of the universe (which is trying to pull them apart). With galaxies that start out quite close together, it is almost always gravity that wins, so in the end the galaxies will collide. This will most likely happen to the Milky Way and the Andromeda galaxy (our nearest large neighbour) in a few billion years.

Baloney!

Gravity may pull them together, but if they are both travelling outward from universal expansion, the collision would be much more tangential, rather than head-on.

Originally Posted by Seraphim

Baloney!

Gravity may pull them together, but if they are both travelling outward from universal expansion, the collision would be much more tangential, rather than head-on.

You base this on what?

The galaxies will be traveling at the same rate so you can ignore that.
All you have left is gravity which will cause the collision.

Karen Masters has a PhD in Astronomy from Cornell. I would think she knows
what she is talking about.

Originally Posted by NYCshaver

You base this on what?

The galaxies will be expanding at the same rate so you can ignore that.
All you have left is gravity which will cause the collision.

Karen Masters has a PhD in Astronomy from Cornell. I would think she knows
what she is talking about.

Ignore massive velocities that cause Doppler redshifting of light?

Originally Posted by Seraphim

Ignore massive velocities that cause Doppler redshifting of light?

Yes if they are both travelling at the same velocity.

Originally Posted by NYCshaver

Yes if they are both travelling at the same velocity.

They are travelling at the same velocity, in the same direction (more, or less...). I get that. But then the gravitational attraction makes they collision course a vector off of that main direction. How could the two massive inertias make 90 degree turns from their original heading, and then end up colliding head-on?

Originally Posted by Seraphim

They are travelling at the same velocity, in the same direction (more, or less...). I get that. But then the gravitational attraction makes they collision course a vector off of that main direction. How could the two massive inertias make 90 degree turns from their original heading, and then end up colliding head-on?

Well I went back and looked at the article you linked too. They never said it was a head-on collision.