8 replies to this topic

[arunma]

Yeah, I tried to make the topic title sound like the title of a physics paper. Sue me. After reading this:

http://cosmiclog.nbc...statistics?lite

Long story short is that the Planck Experiment is a new microwave detector (satellite-based) which has taken better measurements of the cosmic microwave background than its predecessor WMAP. Among other results, the new estimate on the age of the universe is 13.82 billion years, which if I recall correctly is consistent within errors with the old result. Cool, huh?

[Sir Deimos]

Wow. Is it just me or is knowing how old the universe is terrifying? Hahahah.

[wisp]

I find a lot of things about the universe terrifying. If I play around with any of those sky-gazer type programs or relative-size-of-celestial-bodies doohickeys, I get super creepy feelings. I kind of like it though. XD

[arunma]

I'll have to keep reading the actual paper (sorry, I have a real job...and even though my job is astrophysics there are other things I'm supposed to be doing). But I believe that these results do more than just further constrain the age of the universe. They might actually indicate that the CMB has a dipole moment, i.e. it has a preferred direction. What the hell does that mean? Pot of gold at the end of the rainbow or something?

[Egann]

The interesting thing I noted:

The Planck team's breakdown of the universe's constituents is 4.9 percent ordinary matter, 26.8 percent dark matter and 68.3 percent dark energy, he said.

Let me remind you both dark matter and dark energy are basically mathematical fudge factors to make cosmology fit observation. Fudge factors which, in total, outmass and overpower observable stuff 20:1.

Pardon my skepticism. I can't get the word "epicycle" out of my head.

Edited by Egann, 29 March 2013 - 09:11 AM.

[arunma]

The interesting thing I noted:

The Planck team's breakdown of the universe's constituents is 4.9 percent ordinary matter, 26.8 percent dark matter and 68.3 percent dark energy, he said.

Let me remind you both dark matter and dark energy are basically mathematical fudge factors to make cosmology fit observation. Fudge factors which, in total, outmass and overpower observable stuff 20:1.

Pardon my skepticism. I can't get the word "epicycle" out of my head.

Huge difference here. Epicycles are based on the assumption that everything moves in a circle. Dark matter is based on the assumption that the theory of gravity is true. Is that an assumption you'd want to give up?

Also, dark matter can be imaged. The Bullet Cluster is probably the most famous example.

[Egann]

Huge difference here. Epicycles are based on the assumption that everything moves in a circle. Dark matter is based on the assumption that the theory of gravity is true. Is that an assumption you'd want to give up?

Also, dark matter can be imaged. The Bullet Cluster is probably the most famous example.

I was actually referring more to dark energy. At between 50 and 80% off, I think it's totally fair to question if and how much our conventional theory of gravity applies to galaxies, but fundamentally dark matter is a guess that we can't see something and that something acts like normal matter, at least gravitationally.

Dark energy, however, is a whole 'nother beast. Dark energy is a hypothesized energy powering the expansion of the universe, and on paper it's a negative pressure, or repulsive. Considering that the fundamental forces of the universe (electromagnetism, strong and weak nuclear forces, gravity) are either polar or attractive, a purely repulsive energy is immediately suspicious. It doesn't act like matter: it acts like a mathematical fudge factor.

[Mark]

meh, I think with use you get a little numbers immune.
'oh yeah, 13 billion years... *shrug*'
'Avogadro's number, you know, its just 6.02E23'

sometimes i still get the 'bigness' feeling, when considering - say - when i try to visually immagine and count how many oranges i could fit into my workplace, etc.
but otherwise nah.
when you understand the magic, it isnt magical anymore.

[arunma]

Huge difference here. Epicycles are based on the assumption that everything moves in a circle. Dark matter is based on the assumption that the theory of gravity is true. Is that an assumption you'd want to give up?

Also, dark matter can be imaged. The Bullet Cluster is probably the most famous example.

I was actually referring more to dark energy. At between 50 and 80% off, I think it's totally fair to question if and how much our conventional theory of gravity applies to galaxies, but fundamentally dark matter is a guess that we can't see something and that something acts like normal matter, at least gravitationally.

Dark energy, however, is a whole 'nother beast. Dark energy is a hypothesized energy powering the expansion of the universe, and on paper it's a negative pressure, or repulsive. Considering that the fundamental forces of the universe (electromagnetism, strong and weak nuclear forces, gravity) are either polar or attractive, a purely repulsive energy is immediately suspicious. It doesn't act like matter: it acts like a mathematical fudge factor.

Well, no comment on dark energy yet since it's not my area of expertise. But I'd say that dark matter can definitely be seen. Sure it can't be seen directly, but neither can the wind. Quite a few things in nature are seen primarily by their effects, after all. So I'd say that the existence of dark matter is largely settled among astrophysicists. Really the only question is as to the nature of its composition, i.e. neutralino WIMPs vs. something else.