Tag Archives: cosmology

evidence in support of the big bang: #3 olbers’ paradox⤴

from @ fizzics

You might remember that we looked at some paradoxes when we studied special relativity earlier this term.  Here is another situation where a paradox can arise.  The German astronomer Heinrich Olbers (1758–1840) asked why the night sky was dark.  At the time, astronomers believed that the Universe was both infinite and steady state (unchanging), so ... Read more evidence in support of the big bang: #3 olbers’ paradox

evidence in support of the big bang: #2 nucleosynthesis⤴

from @ fizzics

As we worked through the diagram explaining the stages of the Big Bang model, we looked at a section of the diagram where the Universe was hot enough for nuclear fusion.  At this point, hydrogen nuclei were fusing together with other hydrogen nuclei to create helium nuclei.  As the Universe expanded, it cooled and further ... Read more evidence in support of the big bang: #2 nucleosynthesis

evidence in support of the big bang: #1 CMBR⤴

from @ fizzics

introduction to the Big Bang from mr mackenzie on Vimeo. Georges Lemaître’s theory of an expanding Universe, which has become known as the Big Bang, was supported by Hubble’s observations.  The expanding Universe idea was challenged by influential scientists who believed the Universe was both infinite (and therefore not expanding) and steady state (unchanging).  Supporters ... Read more evidence in support of the big bang: #1 CMBR

Perimeter Institute – EinsteinPlus 2016 – Day 2⤴

from @ stuckwithphysics.co.uk

Day 2 of EinsteinPlus 2016 saw the group formally welcomed to the spectacular Perimeter Institute building after an equally spectacular breakfast. (There are two excellent bistros at PI, which provided the group with a fabulous range of meals over the week long visit. I'd say more, but there'd be a real danger of this becoming a food blog...)

The morning session was split into two -

  • Cosmology - this used an existing PI activity 'The Signature of the Stars' from their educational resource on 'The Expanding Universe' - using diffraction glasses observations were made of line spectra from a variety of gas discharge lamps. These spectra are used to identify the elements present in stars, in the Milky way and in distant galaxies. The spectra of light from distant galaxies shows the same spectral lines as stars in our galaxy, but the lines appear in slightly different positions, with longer wavelengths. This effect, known as Red Shift, occurs because the galaxies are moving away from us, and each other, at high speeds. Measuring the red shift for a galaxy can be used to measure its speed, which relates in turn to its distance from us. This effect was first observed in the early 20th century and used to formulate Hubble's Law - which states that not only is the universe expanding, but the further away from us a galaxy is, the faster it is moving. The activity includes data allowing the red shift of a range of galaxies at different known distances to be used to find their speeds. This data is then plotted it give a graph representing Hubble's Law, which gives an approximation of the Hubble constant and can in turn be used to find the age of the universe.

  • Gravitational waves - this used a newly developed activity based around the recent detection of Gravitational Waves at the Laser Interferometer Gravitational Wave Observatory (LIGO) facilities in the USA. The facilities use extremely large scale (~4km) laser interferometers to measure incredibly small expansions or contractions (~10-19 m - 1000 times smaller than the diameter of a proton) of the devices which occur when gravitational waves pass. There are many areas of physics and engineering involved in the development and operation of the LIGO detectors, from the solutions to Einstein's General Relativity which predicted the existence of Gravitational waves, to the intricate suspension of the mirrors sued to improve the sensitivity of the detectors - developed at the University of Glasgow. The activity centres around the properties of waves, and their behaviour when they undergo reflection - beginning with demonstrations of mechanical waves using a slinky. Observations of phase change upon reflection were developed upon and related to the operation of the interferometers at LIGO. These ideas were utilised in a hands on activity to simulate the paths of the laser light used at LIGO in order to find the nature of the light detected when the device is unstretched (no gravitational wave) and stretched. This task offers an excellent opportunity to link this part of the Advanced Higher physics unit on waves to a context which involves real, cutting edge physics.

LIGO unstretched

LIGO stretchedAfter lunch, followed a two more sessions -

  • Neutrino Detection - another new activity, this is based on the Nobel Prize winning work of Professor Art McDonald and his team at the Sudbury Neutrino Observatory (SNOLAB). The session began with an overview of the production of neutrinos in the sun and the difficulty in detecting these particles - the 'Solar Neutrino Problem'. The session continued with a description of the facility at SNOLAB and a hands on task modelling the detector using marbles, cardboard boxes and a baking tray. There was a great deal of discussion about this task, and the nature of the model to describe and explain neutrino detection. Consequently there was a shortage of time for the remaining tasks, dealing with real data from SNOLAB and the theory of 'neutrino oscillation'.

  • Dark Matter - this session used the 'Dark Matter Within a Galaxy' activity from 'The Mystery of Dark Matter' materials. The activity begins with a revision of the basic rules for circular motion and gravitation, using a range of data to find and plot the orbital speed of a star against its radius from the centre of its galaxy. These values, calculated from classical theory, do not compare well with observational data - implying that there must be more mass in these systems that we can not detect - Dark Matter. Whilst the part of the underlying physics of this task, circular motion, is beyond the scope of the Higher physics course in Scotland, it might be fair to use this as a practice data handling task which could be used to exemplify and reinforce the very brief mention of Dark Matter in the 'Our Dynamic Universe' unit.

The final session of the day was a keynote presentation delivered by Professor Avery Broderick from the University of Waterloo on the Event Horizon Telescope (EHT). This program uses nine existing telescopes across the globe and applies a technique known as Very Long Baseline Interferometery (VBLI) to improve the resolution at which images of very small objects can be made.

It is hoped that by improving the resolution for existing telescopes and including planned future telescopes in the gathering and processing of data, the EHT will obtain the first direct images of the event horizon for a black hole in our galaxy. Recent observations in the constellation of Sagittarius are thought to indicate the presence of a black hole with a mass around 4 millions time that of our sun. This black hole is of the right size and at the right distance for the EHT to be able to make observations that will allow an image to be obtained in the next few years.

The data gathered and images obtained by the EHT will allow for further testing of Einstein's theory of General Relativity, and provide a greater understanding of phenomena such as black hole accretion and plasma jets.

After this presentation and another excellent meal the group was offered a tour of the Perimeter Institute building, offering an insight into how the facilities have been designed and developed in order to attract and facilitate the work of some of the world's foremost theoretical physics (not to mention a very large number of teachers and students).

A selection of images of the building will be included in a gallery as soon as I figure out how to make it work...

 

cosmic microwave background radiation⤴

from @ fizzics

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!) ... Read more