The two most commonly used temperature scales are Celsius and Fahrenheit. The Celsius scale, named after Swedish astronomer Anders Celsius, sets 0C at the freezing point of water and 100C as the boiling point of water at 1 atmosphere of pressure — normal air pressure at sea level. The Fahrenheit scale has 32F as the freezing point of water and 212F as the boiling point. With 180F between freezing and boiling that means each degree Celsius is 1.8 degrees Fahrenheit.

Several accounts of the creation of the Fahrenheit scale exist but the general gist is that Daniel Fahrenheit set 0F at the freezing point of a brine mixture, 32F at the freezing point of water, and another point at body temperature around 96F (now 98.6F). He divided up the scale between these points giving a scale with helpful resolution.

It's interesting to think that for most of history there was no comparable way to say how hot or cold something was.

Having spent time on both sides of the Atlantic I've tried to get at least somewhat familiar with both of them. To convert between them in my head, at least around most air temperatures, I use a quick approximation. As 32F is 0C and for each one Celsius you move almost two Fahrenheit, you can roughly go from Fahrenheit to Celsius by subtracting 32 and dividing by 2 (or a little less to be closer). So 50F is approximately 9C (actually 10C), or 86F is approximately 27C (actually 29.4C). Not perfect, but often good enough if you're trying to work out if it'll be hot out. To go from Celsius to Fahrenheit it's the reverse, times by 2 and add 32.

A simple anchor point to keep in mind is that 82F is near enough 28C—you just swap the digits around.

Both scales are now actually defined relative to the Kelvin scale which sets the lowest point of 0K at absolute zero where basically all movement stops. Zero on the Kelvin scale is around -273C. As such the Kelvin scale, though helpful for scientists, is not very practical for talking about the weather.

Fahrenheit and Celsius

Optimism bias is a tendency to believe that things will turn out well in spite of past evidence or circumstances.

It can be extremely helpful. It allows us to attempt things that many may deem impossible. It probably helps drive entrepreneurs even when everyone is doubting them. Optimists are often healthier and happier.

But it can also undermine us. We might overestimate our chances of success because of what we want to happen rather than what's likely to happen. We may feel pressure from others to give a rosier outlook — like when you might underestimate a timeline when speaking with your boss. We might want others to succeed, or they may be paying us money and be hoping for good news. We probably think we'll get more done next week. We probably think we'll be more disciplined than we will be. We might think that this time it'll be different, or that everyone can't be wrong. Or we may be just discounting evidence without realising it.

Related: Hofstadter's Law, survivorship bias, Kitty Hawk moment

Optimism bias

Redshift refers to light being 'shifted' towards the redder end of the spectrum — longer wavelengths — as objects move away from each other. If a light source is moving towards us then light is blueshifted, shifting towards the bluer end of the spectrum, shorter wavelengths.

Imagine waving a spring back and forth to create a wave and then starting to run away – the waves would be stretched longer. Because the universe is expanding 🤯 distant galaxies are moving away from us faster than nearer ones — imagine how the chocolate chips in a cookie move away from each other as the cookie bakes and grows in an oven. By comparing the redshift of light seen from distant galaxies with what we would expect to see it's possible to use redshift to determine how far they are away.

Redshift is an example of the Doppler effect, or Doppler shift, in action. It's more commonly known by the stretching or compressing of soundwaves as, say, an ambulance moves towards or away from you, or how the sound in front of a moving aircraft eventually can produce a sonic boom.

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Redshift