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Fraser
2005-Jun-30, 06:41 PM
SUMMARY: University of Chicago researcher Nicolas Dauphas has developed a new method to calculate the age of the Milky Way by measuring two long-lived radioactive elements in meteorites. By calculating the amount of uranium-238 and thorium-232, Dauphas determined that the Milky Way is approximately 14.5 billion years old, give or take 2 billion. This is a close match for the age of the Universe, calculated to be 13.7 billion years by NASA's WMAP spacecraft. This means that it probably didn't take much time after the Big Bang for large structures, such as the Milky Way, to form.

View full article (http://www.universetoday.com/am/publish/pinpoint_age_milky_way.html)

What do you think about this story? Post your comments below.

wstevenbrown
2005-Jun-30, 07:54 PM
These claims seem too broad to me. I will stipulate that we understand thoroughly the branching reactions and the decay rates here in the static environment of Earth. I do not agree that the production/retention/accretion/destruction rates are well-constrained in thermonuclear environments, or even in interstellar space. A handful of local meteors tells us only the local history. A single halo star tells us the history of one MW halo star, if all our assumptions about spectrally-derived abundances, and about the interstellar medium between us and the star are correct. The U Chi journalist (who did not cite the original paper) may have heard something other than what was said.

Best regards-- Steve

antoniseb
2005-Jun-30, 08:11 PM
I agree that it is tough to really nail this down. If these isotope ratios are in crystals in a single piece of rock, and that rock is shown to be 14.5 +/1 2.0 billion years old, then that shows something solid has been around since about the beginning. If we are just talking about stuff that collected together later, it's a pretty big leap to say there's no way either of the abundances could have been poluted in a misleading way.

CharlesBell
2005-Jun-30, 08:34 PM
I can't help but note that the math seems to work out that the Milky Way was formed before the Universe?? 14.5 > 13.7
:rolleyes: :D

But considering the plus or minus 2 billion years, it must fall in there some where.

I have decided to write the numbers reported on the age of the universe on a sticky note for my office wall, so I can refer to it, everytime I see these type numbers. Its a reminder that these are just theoretical estimates.

lswinford
2005-Jun-30, 09:23 PM
I was just looking over a text, a very dated text, that we were wanting to reprint. They put the age of the universe, in the big bang discussion, at seven billion years. In the discussion of Hoyle et al.'s Steady State universe they say that we can only see some three billion years into space.

A thing or two has been seen since then, LOL!

I'm wondering if I might want to cite this one and double the "reported age of the universe"!

A beautiful thing, old books, while some still hold an amazing amount of value for contemporary consideration, some of them, from a current perspective, are really a funny read at times.

Greg
2005-Jul-01, 06:03 AM
As more and better observations are made, actual data is replacing theory and models and cosmology is becoming more and more of a science. It may be amusing to look back on it now, but think of the instruments they had to use then. Considering that, I think the cosmologists of the day did a fine job with what they had to work with. The same may be said of this era in a few hundred years, but it is less likely that we are far off the mark right now. Then again we have no idea what dark matter or dark energy is.

Nereid
2005-Jul-01, 12:27 PM
Anyone know if the Dauphas 29 June Nature paper is available in preprint form, e.g. in ArXiV?

As the story hinted, the accuracy of the number (and the size of the 'error bars') depends on the underlying theory and assumptions.

A suggestion for folk like lswinford, doing a side-by-side comparison with stuff written decades ago should include a look at overall consistency as well as changes in assumptions and underlying theory. Even today, my impression is that most folk focus on 'the number' (e.g. the age of the universe is x billion years) and gloss right over the assumptions (e.g. H0 is 71 km/s/Mpc, omegaM is ...). This leads to wonderful opportunities for dishonest (or downright ignorant) journos - "Harvard team finds universe 5 billion years younger than Cambridge team!" (I am making this up) or "Indian scientist finds newly discovered star is older than the universe!" - you simply take the raw number from one source and compare it with that from another, ignore the error bars (there are always error bars) and don't even mention the assumptions.

Guest
2005-Jul-01, 01:44 PM
There were 5 arxiv citations for Dauphas yesterday, none of which was the article under discussion-- Steve

Guest
2005-Jul-03, 04:03 PM
Hmm...

I wasn't aware that an error of + or - 2BY out of a total of 14BY constitutes "pinpointing".

Guest
2005-Jul-03, 05:52 PM
Originally posted by fraser@Jun 30 2005, 06:41 PM
SUMMARY: University of Chicago researcher Nicolas Dauphas has developed a new method to calculate the age of the Milky Way by measuring two long-lived radioactive elements in meteorites. By calculating the amount of uranium-238 and thorium-232, Dauphas determined that the Milky Way is approximately 14.5 billion years old, give or take 2 billion.
This entire calculation is flawed.

Many measurements indicate that heterogeneous material formed meteorites. They did not come from a well-mixed average of the entire Milky Way !

1. Meteorites trapped many short-lived radioactive species (Pu-244, Al-26, Fe-60, I-129, etc.) that were produced just before the meteorites formed. The nuclear reactions that make Pu-244 also produce U-238 and Th-232 (the r-process).

2. Meteorite inclusions contain deficiencies (-) and excesses (+) of isotopes made by various stellar nuclear reactions (He-burning, the r-process, the p-process, the s-process, etc.).

Meteorites are not an average sample of the entire Milky Way. The U-238 and Th-232 in meteorites does not tell the age of the Milky Way !

With kind regards,

Oliver
http://www.umr.edu/~om

Nick4
2005-Jul-26, 03:44 AM
Sounds like a plousible theory.