Note: -40C == -40F, so grecy doesn't need to specify the units[1]!

[1] Unless he's using Kelvins.

With a reading of -40, I'm fairly certain* he's not using Kelvins.

[*] Sometimes negative temperatures are used to represent temperatures ABOVE infinity. That's when high-energy quantum states are MORE populated than low-energy quantum states... it's useful for things like making a laser. But I still think it's unreasonable to believe that the temperature outside is -40 kelvin.

What do you mean by 'above infinity'?

In a nutshell, if you put a negative temperature object A in contact with any object B with a positive temperature, energy will flow from A -> B, regardless of how high B's temperature is. This is the opposite of everyday positive temperatures, where energy will flow from the high-temperature object to the low-temperature one. So in a sense you could say that the temperature of A is "above infinity".

Negative temperatures are effectively hotter than any positive temperature, as I understand it.

If he's using Kelvins, I sense a Nobel.

I sense a broken thermometer

Funny you should say that - the reason I said "way past -40" is because all the thermometers I can find don't go past -40.

Even the digital ones just say "-40.0C" at about 6pm, and won't show anything else until 17 hours later when the sun comes back, and they creep up a few degrees.

Someone else just mentioned it, but I used to live in northern BC and our "red liquid" thermometers recorded temps down to about -60C or so. Coldest I can recall as a kid was -54C. We still walked to school.

Awesome, I'll have to keep a lookout for one.

I rode my bike in yesterday at around -45C. The snow drifts were too big today, so I walked for 35 minutes instead.

I'm curious, do you use mountain bike tires to get more traction in the snow, or are you able to use the small, thin street tires so long as the snow is sufficiently slushy/salted/shovelled?

I ride a mountain bike, though my tires are only normal width. I did put studs in my tires to help with icy conditions.[1] So far I've had a good winter of riding.

I don't think anyone would ever ride a road bike in the winter, it would not be possible with the snow the way it is (deep, often drifting, rarely cleared)

Tons of people up here ride "fat tire" winter bikes with up to 4.5 inch tires. They ride the downhill trails right through winter.

[1] http://www.youtube.com/watch?v=GI-fR2tXR_8 (I used a cordless drill and just drove them through - took 30 minutes all done)

For mercury thermometers, it's because mercury freezes at -38C (-37F). Alcohol (red liquid) thermometers should work to -70C (-94F).

It's not clear why your thermometers don't register below -40, unless it's a legacy of the mercury thermometer limitation baked into the product (or frozen in, so to speak).

That sounds quite extreme... What do you do for living?

I'm a Software Engineer, so I'm inside all day.

I also ride my bike to work every day, and I ski patrol at the local mountains on the weekend.

I went camping in -35C two weekends ago, it was great!

I think I'd rather camp at -35C than at 2C with driving rain and wind - which is far more likely here in Scotland! (-35C is about the coldest I've experienced at altitude in the Alps).

2C with driving wind and rain is fine once you get in your tent. -35C, not so much.

One of the hardest things to deal with is condensation and sweat - anything even remotely damp (socks, sleeping bag, boots, gloves) will be frozen rock solid in the morning.

I stand corrected!

I have no experience of camping in temperatures as low as -35C. However, I have found that camping in Scottish mountains it is much more pleasant when it is in the range 0 to -10C than just above freezing.

I'd quite like to live for a while in place like this, especially if there's a ski resort nearby (or the opposite – on a tropical island).