online

Just getting the scale straight in my head, so I can explain it all to my 9-year-old!

Right now, if I’m not mistaken, about 5% of the universe’s total energy has been observed by its influence on photons. 25% more can be accounted for only by its gravitational influence, so that’s the actual current amount of “dark matter”. 70% is dark energy (the mysterious thing that’s responsible for the expansion’s acceleration).

I just checked with my wife, (who is a historian of astronomy), and she confirmed that Vera Rubin does have a daughter named Judy, so I’m guessing that’s who Buzz went to school with.

Whoa, your class mate’s mom discovered dark matter? That’s another thing that’s been puzzling me lately… It’s my understanding is that astronomers first realized back in the 30′s that galaxies didn’t have enough mass to behave the way they were behaving. My impression is that this problem remained in the forefront right up to today. So my question is, what event constituted the “discovery” of dark matter?

Is this the primary evidence for the existance of dark matter?

But beyond that, we still don’t know whether terrestrial planets are common, or how many are on sufficiently circular orbits to give a fairly stable climate, or what the real habitablity range is for those kinds of planets (since atmospheric greenhouse feedback relations can stabilize a temperature over a wide range of distances from the star).

We also don’t know if you need a terrestrial planet? How about a jovian moon? How about the atmosphere of a jovian planet itself? Both of these are at least worth considering as places for life to develop.

Lastly, we don’t know even know if you really need liquid water conditions for life. There are some lovely liquid methane lakes on Titan (see today’s Astronomy Picture of the Day) that look pretty inviting, provided you don’t mind a temperature of 93K.

I think that we will have a much better idea of the likelihood of life elsewhere once we have more thoroughly explored the solar system. If there really isn’t any life in the oceans of Europa or the lakes of Titan, and there really aren’t any fossils in the sedimentary beds on Mars, then maybe we can say that life is rare. On the other hand, if life developed just one more place in our solar system, then I’d bet it is common throughout the universe. After all, if you get it twice in one little solar system, it be easy to get the right conditions.

Ausrick, before you get too discouraged, remember JBS Haldane’s comment after a lecture on the habitable zone around stars: “But what if they (alien life) look like bloody stones?”

Nice picture, it seems Hera’s breast has many heirs.

Just curious.

Also you’re assuming the galaxies are falling inwards, whereas in all likelyhood the galaxies in this cluster are moving too fast to remain in the cluster. Over time one would expect the cluster to fall apart.

ioresult Says:
Skeptigirl: The universe is pulling away from us at the same speed and acceleration whichever direction we look. According to your idea, that would mean we should be surrounded by black hole matter further than 14 billion light years away in every direction. This can’t be: the gravitational field inside a massive hollow sphere is flat, there is no pull in whatever direction. So even if there were black hole matter all around us, it wouldn’t affect the universe’s expantion. That puts us back at thinking about the cosmological constant, or the quintessence, or dark energy (however you may want to call this thing that ir ripping the universe appart).

I’m aware of the dif in expansion and movement. I told you it was naive speculation. I suppose I wasn’t taking into account the fact redshifts don’t suggest any gravitational point of attraction. Back to contemplating….

Gravity inside a hollow sphere. Do this google search: “gravity inside hollow sphere”. It sould yeld a couple of interesting texts.

About the universe’s quintessence: type “Quintessence (physics)” in wikipedia.

Skeptigirl:
The universe is pulling away from us at the same speed and acceleration whichever direction we look. According to your idea, that would mean we should be surrounded by black hole matter further than 14 billion light years away in every direction. This can’t be: the gravitational field inside a massive hollow sphere is flat, there is no pull in whatever direction. So even if there were black hole matter all around us, it wouldn’t affect the universe’s expantion. That puts us back at thinking about the cosmological constant, or the quintessence, or dark energy (however you may want to call this thing that ir ripping the universe appart).

You said, “whereas in all likelyhood the galaxies in this cluster are moving too fast to remain in the cluster. Over time one would expect the cluster to fall apart.”

If they are moving too fast to remain in the cluster, then that means they aren’t gravitationally bound, doesn’t it? If they aren’t gravitationally bound, then how did they come to be a cluster in the first place? Maybe you or Phil could explain this.

From a statisticians point of view, what I’ve been reading seems a little more lonely–that chances of other habitable planets occuring seem to diminish with every new discovery. The last paper I read had quoted something like there being 202 parameters that need to fall within very specific guidlines to form a habitable planet (another paper only said 120, but I think it was written earlier). It seems that everthing from the metal content of the star to where and when gas giants form and what type of orbit they have seems to have an effect on planetary formation models. and they quoted the statistical probability of another habitable planet occurring as 1 in 10^140. I also heard by comparison that there are supposedly only about 10^76 protons in the universe. (this last one is hearsay, I’ve seen it a number of places, but not in a scientific journal and have no idea the context… I’m sure the amount of protons estimated in 1970 would probably be different than the amount estimated today.)

Now I admit, these numbers seem out of whack to me, but to be honest my mind can’t truly conceptualize them anyway… and with every advance or discovery they change as do the models that seem to generate them. So I see how some one could say they would tend to believe we are alone and I can easily see why someone would say the opposite.

I’m really only qualified to say the universe is awe inspiring and humbling… and I think that galaxy on the lower right side of the picture is pretty Oh, and to echo that it makes you think about things like this to begin with… before seeing this picture I was only concerned with where I sat my Mountain Dew. Thanks Phil!

Fantastic Images!