Lecture 01: A Grand Tour of the Universe

[williamnbaudinet]

Two thumbs up for the presentation. Learned a lot from it.

[jasperb]

Hello

I downloaded the video and watched until about 9.20
and the video stopped working. Is there another copy or
a certain media player which will avoid this?
I have tried using quicktime and VLC to play the video.

Thanks
J

[owlice]

Jasper, you can watch it on YouTube here: http://youtu.be/OO7qvAETCMs

[Scottyboybc]

thanks for the free material, it's appreciated!

[LocalColor]

Just discovered this class - glad this is still available to us. Thank you!

[objetivonocturno]

Thanks

[addseo1115]

Thanks for sharing the good lessons here. Nice to see

[dllamas]

Thanks for share

[shastriarvind88]

hi ,
very interesting topic discussion .i myself very keen to know more about Universe.i want explore it.

[jaydcx]

To Bystander on the size of the Universe... Physicist here!
The universe appears to be 13.7 billion years old, by the farthest objects we can observe as determined by red-shift.
However, it is not necessarily appropriate to consider how much larger it is now, just because 13.7 billion years have gone by (since those furthest objects emitted photons) and those furthest portions are supposed to have kept traveling at least as fast as when we observe these boundary objects here on earth now, much later.
That's because of the intersection of several physics laws and astronomy: the expansion of the universe appears to be speeding up; so that those far objects are not now where they were 13.7 billion years ago. In all likelihood, those furthest objects lie outside of our observable universe because the accelerating expansion of space has carried them into regions that are receding from us FASTER than the speed of light! So light coming back toward us emitted now, will never get to us... Light emitted in our direction is red-shifted away to zero frequency... never gets here!
This is similar to case of light approaching the event horizon of a black hole, getting red shifted so far that it also does not escape the black hole once it gets to the event horizon. The light headed for the black hole does indeed go into the black hole, crosses the event horizon in a finite time in it's proper frame of reference, but we just never get to see it because it is red-shifted away.
Another problem with deriving current size is the whole notion of simultaneity: it is fraught with erroneous assumptions as we cannot really physically define what it means to say that light that was emitted from distance at edge of 13.7 billion years will, right now, synchronous to us, start to travel our way... Why? The special theory of relativity! What appears as simultaneous to one observe will not be so to another one moving with a considerable relative velocity in another frame of reference... Our minds can of course think of such simultaneity, but defining it physically may not be possible.

So yes the universe is probably quite larger than 13.7 * 2 billion light-years diameter by now, but the fact is we don't know how much, and we suspect that some of that is already past our event horizon in space into which it has traveled, space receding from us faster than the speed of light. It's no longer within our observable universe. But guess what? Doesn't that tell us that the entirety of the universe is just not or ever observable to us? Unless of course it stops, and then turns around and re-compresses in a big crunch.

[KennerKenny]

Definitely learning a lot from here. Thanks!