Comments on: The cosmic distance ladder

By: The Cosmic Distance Ladder (version 4.1) « What’s new

The Cosmic Distance Ladder (version 4.1) « What’s new — Sun, 10 Oct 2010 18:40:44 +0000

[...] once at UCLA. The slides I used were similar to the “version 3.0” slides I used for the same talk last year in Australia and elsewhere, but the images have been updated (and the permissions for [...]

By: Patrick

Patrick — Mon, 12 Jul 2010 04:43:00 +0000

On slideshare: http://www.slideshare.net/embeds/cosmic-distance-ladder-terrance-tao-updated-102609

By: Nurdin Takenov

Nurdin Takenov — Fri, 02 Jul 2010 14:15:44 +0000

Good presentation, I finally ralized the Aristarches’ method.
Slide 24: “Aristotle also knew there were stars one could see in Greece but not in Egypt, or vice versa.” – hm, it seems that all stars senn in Greece also seen in Egypt.
Slide 41: “Aristotle argued that the Moon was a sphere (rather than a disk) because the terminator (the boundary of the Sun’s light on the Moon) was always a circular arc.” – isn’t the arc of terminator is elliptical?

By: Diego

Diego — Tue, 11 May 2010 14:44:13 +0000

Dear Terry,
Thank you for your reply. Yes, I see your point. However, going down from the everyday scale to the atomic level by means of an electron microscope is like going up from the everyday scale to “the universe scale” (9th rung in your slides) by means of the Hubble telescope. It skips a lot of rungs (e.g. the width of a human hair, the edge of a very sharp knife, the porosity of crystals, the nano-scale, etc.) With my question I meant “homemade” or “just clever” ways to conceive the smallness of things along the lines of the ancient Greeks’ techniques.
Perhaps in the future we will be able to measure the width of the Kaluza-Klein compact dimensions in a lab with a gigantic machine. That would be fun.
In terms of waiting time, yes, galaxies take a long time to return our calls; but it could easily take us a longer time to measure small lengths near the Planck length (about 10^20 times smaller than the diameter of a proton, according to wikipedia).
Although that might all be mere speculation, it would be entertaining to illustrate their corresponding scales, as an exercise in numerical literacy…

By: Terence Tao

Terence Tao — Tue, 11 May 2010 06:08:10 +0000

Well, it is much shorter; with electron microscopes, for instance, one can already get down to the atomic level, and below that range one can more or less compute everything from quantum field theory, using collider data and known values of physical constants to calibrate. The big difference is that we can study microscopic objects in a laboratory, and subject them to whatever physical tests we please in a reasonable amount of time, but we cannot send out some test or probe, say, a distant galaxy without having to wait millions of years for the result.

By: Diego

Diego — Tue, 11 May 2010 04:13:05 +0000

Hello Terry,
I keep coming to your wonderful slides on the cosmic ladder. I wonder, is there anything like a “microcosmic ladder”? That is, going smaller rather than bigger.

By: Estelle

Estelle — Fri, 02 Oct 2009 00:29:11 +0000

page 19, Aristotle (384-382 BCE)… [Oops! That should be 384-322 BCE, thanks. The next update of the slides will have the correction. -T.]

By: Nicole

Nicole — Tue, 08 Sep 2009 23:37:29 +0000

I thoroughly enjoyed your lecture at QUT yesterday and found the ancient methods of calculation fascinating. Was a bit miffed not to have brought something to take notes on, so you can imagine my delight and gratitude that you have made the slides available here! Thank you so much.

By: Clay-Mahler lecture series « Mathematics in Australia

Clay-Mahler lecture series « Mathematics in Australia — Mon, 07 Sep 2009 03:29:02 +0000

[...] Here are the slides for the public lecture “The cosmic distance ladder”. [...]

By: David

David — Sat, 05 Sep 2009 09:17:17 +0000

Define the universe:)