27 February 2019

Sixteen Candles

If you're not watching "How the Universe Works", you must turn in your geek credentials. While "Parts Unknown" was the best show on the TeeVee, "Universe" is the most interesting. From what I can tell, each 'new' episode is cobbled together from past segments stitched with one or two new ones. Yesterday dealt with dark matter, dark energy, and the End of It All.

So, I read today's NYT, which being Tuesday has the "ScienceTimes" extra section, and there is a Dennis Overbye piece on the front page and most of the back page. Dealing with the self-same topics. Much of the text could have been from the "Universe" episode (or vice versa), which makes sense given that the science is just a bunch of facts.

Hubble discovered universe expansion in 1929, but in 1998 it was found that the expansion was accelerating. How that can be is the subject of the "Universe" episode and much of the article. What caught my attention in the article was this:
But to calibrate the Hubble constant, astronomers depend on so-called standard candles: objects, such as supernova explosions and certain variable stars, whose distances can be estimated by luminosity or some other feature. This is where the arguing begins.

For some years, I'll guess from the time I first heard about acceleration, I wondered how that could be known. Expansion is deduced simply from red shift, but acceleration requires a benchmark to make the comparison. That's the standard candle. I never bought that such a thing could actually exist, from the point of view earthlings being able to measure such. To do so we need to know both the local (to the distant object) luminance and the distance from here to there.

The article spends some time attempting to nail the standard candle down. I'll leave it to the reader to decide whether it's been nailed.

No comments: