Topic: Isaac Asimov - Please Explain!

[The Bar-Abbas Anomaly]

 
My understanding was that "Dark Matter" was the latest big mystery in cosmology - We have detected more gravity in the universe than we can account for by what we can see in the radio spectrum so the theory goes that there must be a whole lot of gravity source out there that we just have not yet been able to detect...

But then this evening I read the cover story in Parade Magazine (yes, the one that comes with your Sunday newspaper) and it was all about 'Dark Energy'.  At first I thought they were refering to Dark Matter, but that's not it.  Apparently Dark Energy is some force that is contrary to gravity and is pushing stuff apart faster and faster...

So, like, I'm confused.  Is Dark Matter passe'?  Is there too much gravity in the universe or too little?  How do these two things relate?  Should I stop getting my science news from Parade Magazine?

 

[Lieutenant_Q]

Should I stop getting my science news from Parade Magazine?  Definitely.

I heard a lot around season 6-7 of VOY saying that Dark Matter didn't actually exist.  Although a lot of it was in passing.  I remember looking briefly and then saying to myself, why do I bother?  It's like trying to figure out what is healthy for you to eat.  Wait two days and what you thought was good for you is suddenly bad for you.  What you thought was going to drive you to an early grave will help prolong your life.  Wait two more days... 

[manitoba1073]

think of it this way and it will be easier for you.
 Yes both exists, there is dark matter and dark energy, However there main differences are rather simple form is like the opposite ends of a magnet. ones a positive side and ones a negetive side.

[Nemesis]

I'm not really up to date on this and there are others who could do better but I'll make a brief stab at it.

Dark Matter and Dark Energy are not usually viewed as being related.

Dark Matter

There are 2 basic reasons for the idea of Dark Matter. 

1. Assuming the Big Bang theory is true the universe needs a certain mass to be closed (that is for it to eventually collapse again rather than expand infinitely) and a significant amount of the minimum mass has yet to be found.  Not finding the mass does not invalidate the big bang but does mean that there will be no follow up bangs - this universe eventually dies and is not reborn.

2. Gravity theory is known to have problems and dark matter can be used to explain them.  For example the outer parts of galaxies orbit the core too fast for the detected mass.  The inner parts behave correctly (by currrent theories).  Also the 3 probes that the U.S. has way out towards the edge of the solar system are off course in a way that indicates that gravity is stronger out there than theory says.  Dark matter can again explain it.

The form of dark matter is different for different theories and has yet to be proven to exist.

Dark Energy

Galaxies occur in clusters and those clusters behave normally within the clusters.  Clusters of galaxies are receding from each other.  One explanation is Dark Energy as a repulsive force propelling matter away from each other and which is stronger over long distances than is gravity.  Within a galactic cluster gravity is too strong in the tens of millions of light years between galactic clusters the replusive force dominates.  Again not yet proven.