Author Archives: mrmackenzie

dosimetry⤴

from @ fizzics

This week, we’ve looked at calculating radiation doses.  The absorbed dose D, measured in Grays (Gy), takes into account the energy E absorbed and the mass m of the absorbing tissue. The higher the energy, the greater the absorbed dose.  If you are wondering why the absorbing mass is important, consider the different masses of ... Read more dosimetry

how will the Universe end?⤴

from @ fizzics

It’s complicated and cosmologists are not certain.  One of the issues is only being able to see about 4% of the mass in the universe – the stars, planets, gas and dust.  About 25% of the mass of the universe is Dark Matter.  It’s “dark” because it doesn’t emit light that enables us to see ... Read more how will the Universe end?

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

the Milky Way is not alone⤴

from @ fizzics

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 ... Read more the Milky Way is not alone

evidence that special relativity is real⤴

from @ fizzics

For the past two weeks, we’ve been looking at equations that describe time and distance changing according to speed. It’s been quite heavy on theory and maths with no supporting evidence to suggest Einstein’s ideas were correct.  I want to address that lack of evidence by pointing you to some practical work that had been ... Read more evidence that special relativity is real

applications of satellites⤴

from @ fizzics

By now you should have watched the video about satellites.  This screenshot showing a satellite passing over the Highlands was taken from about 17 minutes into the programme – did you notice at the time?               It was quite eye-opening to see just how much modern society relies on ... Read more applications of satellites

re-entering the atmosphere⤴

from @ fizzics

In space there is no air resistance to oppose motion, so the Space Shuttle orbiter could travel at very high speeds, up to 17,000 mph!  At these speeds, the orbiter experienced enormous air resistance as it descended into the Earth’s atmosphere at the end of its mission. Air resistance is just like any other form ... Read more re-entering the atmosphere

x-rays⤴

from @ fizzics

X-rays are a form of electromagnetic radiation.  They have a much higher frequency than visible light or ultraviolet.  The diagram below, taken from Wikipedia, shows where x-rays sit in the electromagnetic spectrum. image by Materialscientist Wilhelm Röntgen discovered x-rays and the image below is the first x-ray image ever taken.  It shows Mrs. Röntgen’s hand and wedding ring.  ... Read morex-rays