100 years of general relativity


It seems general relativity is 100 years old today. We’ve been struggling a bit with this topic, so I thought these videos might help.

Why Einstein is such a big deal from Fusion Media Network on Vimeo.

General relativity explained in under 3 minutes from Fusion Media Network on Vimeo.

Science Museum – Einstein’s Cosmos from ORDER Productions on Vimeo.

#Einstein100 – General Relativity from Eoin Duffy on Vimeo.

cosmic microwave background radiation

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 is so long that the background radiation lies in the microwave portion of the electromagnetic spectrum.

The CMB was first detected in 1964 by Richard Woodrow Wilson and Arno Allan Penzias, who worked at Bell Laboratories in the USA.  They were building a radio wave detector when they found a source of noise that seemed to come from every direction.  That the noise came from every direction ruled out a specific star or galaxy.  They were also able to rule out the urban environment but…

“then they found droppings of pigeons nesting in the antenna.  They cleaned out the mess and tried removing the birds and discouraging them from roosting, but they kept flying back.  “To get rid of them, we finally found the most humane thing was to get a shot gun…and at very close range [we] just killed them instantly.  It’s not something I’m happy about, but that seemed like the only way out of our dilemma,” said Penzias.  “And so the pigeons left with a smaller bang, but the noise remained, coming from every direction.”       source: NPR.org

Here are Wilson and Penzias next to their detector.  From the size of the detector, you can see why pigeons might find it a good place to stay.

Screen Shot 2015-11-23 at 20.11.01

image: arstechnica.com

Wilson and Penzias shared the 1978 Nobel Prize for Physics for their discovery of the CMB.  Many of the images we see of the mapped CMB have been provided by a European Space Agency mission called Planck.

Now get some popcorn and watch these videos about the cosmic microwave background.

star colours

Astronomers often refer to the colour of a star, which seems a bit odd because we mostly see stars as white twinkly objects.  However, even with the naked eye, we can look closely at certain stars and detect a hint of colour – just look at this image of the Orion constellation.  As we view him, the left shoulder has a red coloured star, while the right shoulder and right foot appear to be blue.


image: Orion 3008 huge.jpg, Wikipedia

Now click on the image to see the same view at much higher resolution.  In the hi-res photo, look at the stars in the background.  They’re not all white!

What can the colour of a star tell us?

The apparent colour of the star tells us something about its temperature.  The hotter the object, the shorter the peak wavelength emitted by the star, as shown in the graph below.  This relationship is called Wien’s Law.

Although this relationship is not provided in the CfE Higher relationship sheet, there is potential for a graph question relating to Wien’s Law.


image: Wien’s Law, Wikipedia

It might be easier to see the emitted wavelengths projected against the visible part of the electromagnetic spectrum.  Here, the wavelengths are given in an alternative unit – Ångstroms (10 Å = 1 nm).  Our Sun is a typical yellow star, so its emission would be represented by the middle star in this image.

Screen Shot 2015-11-22 at 18.39.13

image courtesy of kstars, kde.org – colour is exaggerated

The colour of a star also tells us something about the expected behaviour of a star, it’s lifetime, and destiny.  This is achieved by plotting the stars on a Hertzsprung-Russell diagram.  More about HR diagrams here.

Test your understanding of the HR diagram.

This excerpt of Seven Ages of Starlight looks at the HR diagram and uses it to tell us something our Sun’s fate.

starlight – part2 from mr mackenzie on Vimeo.

In case you were wondering, we get red stars, orange stars, yellow stars, and blue stars.  But not green stars.

nat5 latent heat of fusion/vaporisation

Those experiments to determine the latent heat of fusion and latent heat of vaporisation for water bring the dynamics and space unit to a close.  Here is a copy of the handout we used in class.  You will be tested on this unit in your double period next week, so please remember to download a copy of the summery notes to help with revision this weekend.