Friday, November 11, 2005

Stretchy, stringy questions

When relating a story or giving a presentation, did you ever "get ahead of yourself" the saying goes? Well, that may be the closest you ever get to to time travel! But the topic of time travel is fascinating -- as are related realms of physics -- and certainly puts more mundane earthbound happenings into perspective.

Here are a few sites with some VERY nice multimedia demonstrations and explanations of this sort of thing:

  • Einstein Light - multimedia modules that present the main ideas of relativity, with background info about mechanics and Galilean relativity; electricity, magnetism and relativity (Maxwell); the principle of Special Relativity; relativistic mechanics leads to E = mc2 ; how relativity implies time dilation, and more.
  • The Elegant Universe - a fascinating and thought-provoking journey through the mysteries of space, time, and matter. Brian Greene's excellent 3-hour visual feast, with outstanding graphical animations explaining string theory (alias "the theory of everything").
  • Superstring Theory >> Cosmology >> Take a trip through the Big Bang >> Black Holes
You'll find some more links like this, towards the bottom of the page at ... or its mirror/backup USA site

I really like the explanations given by physicist Joseph Wolfe of the University of New South Wales (in Australia) at the Einstein's Light website. For example, at (in the section called Is time dilation true? How big are the effects?) there's this interesting example:
"Some particles striking the Earth's upper atmosphere have energies that exceed 2*1020 eV. If such particles are protons (with mass of about 1 GeV), their speeds would be 0.999 999 999 999 999 999 999 995 c. For them, g is 1011. Now the age of the universe is about 13 billion years for us, but for such particles, the age of the universe would be about (13 billion years/1011), ie about a month. Such a particle could cross the visible universe in a matter of months (their time)."
You'll have to read the rest of the article to see this in context, but it's a sobering thought all the same.

Wednesday, November 09, 2005

How wide is the Universe?

Is the universe bound to be twice as wide across, measured in light year units, as it is old (measured in years)?

The universe is reckoned to be some 13 billion years old. Does it follow that it must be some 26 billion light years across?

(This would presumably be a result of spreading out in all directions at the same speed following the "Big Bang" ... See some musings about my state of growing ignorance in this posting at my other blog: Blissfully getting to know less about everything )

NOTE: see an update to this post at:

How Wide is the Universe? - revisited