## Scholar tutorial for ODU unit assessment

The Scholar tutorial is on Monday 14th November, starting at 6pm.  You can join the room from 5.30pm using the link on this page.

## Hubble discovers our universe is expanding

In the 1920s, Edwin Hubble had access to the Hooker telescope on Mount Wilson, Los Angeles.  This was the largest telescope in the world at that time.  His first breakthrough was the discovery of a cepheid variable star in the Andromeda nebula.  This enabled him to calculate the distance to Andromeda and he quickly realised this was not a nebula but a galaxy outside the Milky Way.
This video follows his work.

Hubble then turned his attention to other galaxies, looking for cepheid variable stars that would allow him to determine their distances from the Milky Way.  He used redshift to calculate their recession velocity and plotted a graph against distance.

He found that the recession velocity (v) was directly proportional to distance (d).  We can express this relationship as

$v = H_o d$

where $H_o$ is the Hubble constant.  Astronomers agree that the current value of the constant is

$H_o = 72 kms^{-1}Mpc^{-1}$.

Since this is a  SQA course, we need to convert into SI units – giving

$H_o = 2.3 \times 10^{-18}s^{-1}$

In this video, Professor Jim Al-Khalili looks at Hubble’s work on the expanding universe.

Although he was American, Edwin Hubble transformed himself into a tea drinking, pipe smoking, tweed wearing Englishman during his time as a Rhodes Scholar at Oxford.  He probably wouldn’t approve of this last video.

Unfortunately, astronomers were not eligible for the Nobel Prize for Physics.  The rules have now been changed.

## redshift

more redshift

and Yoker Uni’s video about Doppler and stuff

While redshift can be used to tell us about the recession velocity of (non relativistic) galaxies, we also need to find a way to measure the distance to these galaxies.  Astronomers have two main methods to measure these distances; parallax (more parallax here) and cepheid variable stars – there’s a Khan Academy video on cepheid variable stars.

## special relativity

This video follows Einstein’s thought process as he worked through his special theory of relativity.

special relativity from mr mackenzie on Vimeo.

time dilation

another take on special relativity and the twins paradox

…and the Glesga Physics version

length contraction

This video has helpful examples to explain length contraction.

Sometimes it’s easier to imagine we’re a stationary observer watching a fast moving object go whizzing past.  For other situations, it’s better to put yourself into the same frame of reference as the moving object, so that everything else appears to be moving quickly, while you sit still.  The muon example in this video shows how an alternative perspective can work to our advantage in Special Relativity.

Another way to think about this alternative frame of reference is that it’s hard to measure distances when you yourself are moving really quickly.  Think about it, you’d get tangled up in your measuring tape like an Andrex puppy.

###### image: trotonline.co.uk

It would be far easier to imagine you’re the one sitting still and all the objects are moving relative to your position, as if your train is stationary and it’s everything outside that’s moving.  That keeps everything nice and tidy – including your measuring tape.  Got to love Einstein’s postulates of special relativity.

## revision notes for higher ODU resit

I’ve attached a set of notes to help with your revision for the Our Dynamic Universe resit on Tuesday.  Remember that the resit paper will have knowledge questions only, so focus on the unit content during your revision rather than practising numerical problems.

Thanks to Mr Noble for sharing his ODU notes.

The cosmic microwave background radiation (CMB) is radiation left over from the big bang.  When the universe was very young, just as space became transparent to light, electromagnetic energy would have propagated through space at a much shorter wavelength.  Nowadays, the temperature of space has fallen to approximately 2.7 K (that’s 2.7 K above absolute zero!) and, using Wien’s Law, we can confirm that the peak wavelength of the electromagnetic radiation is so long that the background radiation lies in the microwave portion of the em spectrum.

The CMB was first detected in 1964 by Richard Woodrow Wilson and Arno Allan Penzias, who worked at Bell Laboratories in the USA.