eli5: Why is it temperatures can go up to the trillions but only down to -273?
In: Physics
Temperature is related to energy. A particles can be at it’s lowest energy at 0k. Note: even if there is a particle in an environment that has a temperature of 0k, the particle would still have movement. You still cannot break the uncertainty principal.
There is also an absolute got (plank temperature). This temperature has a value of
1.416785(71)×10^32 k. A bit higher than trillions…
You get this by using the plank length (the smallest distance) to calculate the smallest wave length which then corresponds to the highest frequency of a vibration. You can then use this frequency to calculate the associated energy and use the calculated energy to get a temperature.
Theres basically a small temperature range where atoms are solids, a minuscule range below that where theyre wacky, a small range where theyre liquid, and then an absurdly huge range where theyre gasses. Because our form of life needs solids liquids and gasses we have a limited scale to measure things with, if we were beings of pure gas we might make the scale more centered around the actual range of possible temperatures.
This is a weird question to answer because there really is no solid answer: “Why can most things in our daily life get A LOT hotter, but not a lot colder?” Well, that’s just the reality we exist in.
Technically, bonds that hold molecules together (and thus you and I together) can’t exist at very high temperatures. Therefore, anywhere there is life, things would have to be quite “cold” on the universal scale (much cooler than millions of degrees).
In general, most of space is “cold” (much closer to -273 than millions of degrees Celsius) and earth sits in the middle of empty space this earth is relatively “cold” to. So, since we humans were born on a planet much closer to -273 to millions of degrees, we acclimated to temperatures around that level and designed our systems that way. That’s about it.
We just happen to live around the lower end of the spectrum in terms of temperatures across the universe. Life gets harder to support at higher temperatures for a number of reasons, one being that things start to become unstable, they have so much energy at those higher temperatures molecules literally breakdown or react more readily with others.
Another way of looking at it is, temperature can be measured in Kelvin, which ranges from 0 to (trillions) humans evolved on earth, where temperatures range relatively close to 0K (on a cosmic scale). We live roughly between 273K and 300K. We call those temperatures 0C and 27C because it’s just more convenient to use a scale that’s based around our normal temperature. Using a celsius scale, the coldest you can get is -273C.
A civilization that evolved to live at 1 trillion K might ask why temperatures barely ever get hotter than “normal temperature”, but can go all the way down to -1,000,000,000,000
Think of it as temps measure something, like a pile of bricks. You can always add a couple more bricks. But once there are no bricks, you cannot remove any.
We could have a scale that start’s with 0 and then 1 is freezing point of water and all the rest are just increments of the same with few decimals and you are like “shit, it’s 1.134 degrees outside!”
There is a reason we do things like we do
You could move millions of miles per hour but the slowest you can move is 0.
Except, in this case, we call the state of no movement -273 degrees Celcius.
Note: In Kelvin, 0 is the state of no movement.
I think the best ELI5 level reason comes from thinking about gases. Briefly, what we call absolute zero is the temperature where a perfect gas (an imagined ideal situation where the gas will never become a liquid,and the atoms/molecules take up zero volume on their own) occupies zero volume and exerts zero pressure.
Suppose you have some helium gas in a sealed container. You’ll make sure gas is held at constant pressure and let the volume change as you change the temperature. When you decrease the temperature you’ll see the volume gets smaller. If you decrease the temperature by 10 degrees, the volume will decrease by some amount, say 10 mL. If you decrease it by 20 degrees, the volume decreases by twice that amount, so 20 mL smaller. 30 degrees, three times the decrease. You can do this over a very large range of temperatures. Suppose we plot volume on a vertical axis and temperature on a horizontal one. We’ll see a straight line forms – increasing temperature leads to increasing volume, decreasing temperature leads to decreasing volume.
Your volume can get as large as it wants. We don’t know if there’s a limit to how big space is, so we can imagine taking the temperature and volume as high as we want. But the smallest volume the gas can occupy is zero. Negative volumes have no meaning. This means if we draw our line back to where it hits zero volume, we’ll have the lowest temperature that makes any sense at all.
This would be interesting, but what makes it remarkable is if we switch helium for argon, or neon, or hydrogen, or any gas (as long as we stay far away from where it turns into a liquid) we will find it’s the same lowest temperature for every one. If we change our experiment and hold volume constant while measuring pressure we get a similar argument and we find the same lowest temperature. This temperature seems to be a floor for gases. If we use gases as our thermometers, we’re going to see a lower bound. There are more involved arguments regarding statistical mechanics that show a lower bound on temperature as well, but they are beyond the scope of an ELI5.
I want to address one other thing. Lots of top level comments are talking about temperature as a measure of the motion or vibration of the molecules. This is wrong.
To illustrate my point, consider a pot of water. You heat it up to boiling. Well below the boiling point you see lots of tiny bubbles in the bottom. This is dissolved gas coming out of solution. After a time, the water starts to bubble again and you get into normal boiling. It doesn’t have to be a rolling boil. Just a nice, steady change from liquid to gas with bubbles forming at the bottom of the pot and rising to the top and the temperature holding steady. The gas in these bubbles is (very nearly) pure water vapor. The temperature of the liquid is quite close to 100 C, depending on the air pressure, but so is the temperature of the gas in a bubble. The molecules in both situations are water molecules, but those in the gas phase are moving a heck of a lot faster than those in the liquid phase. If they weren’t, they couldn’t have separated from one another enough to form the bubble. We have a situation where the gas is at 100 C, the liquid is at 100 C, but the kinetic energy of the molecules in the gas phase is tremendously larger than the kinetic energy of the molecules in the liquid phase. So, temperature cannot simply measure how much the molecules are moving. It is far more subtle than the textbook discussions.
The idea that it measures “average kinetic energy” comes from other details about the ideal gas model I used to lay out absolute zero. In an ideal gas the only place you can put energy is in the kinetic energy of the molecules. If we have other buckets to dump the energy into, then the ideal that temperature measures average kinetic energy fails.
Source – I’m a physicist.
Imagine you have a car. It’s a really fast car, but for some reason, the car has a speedometer that shows 0 at 100 km/h.
If you slow down 10 km/h from “0”, the speedometer says -10. Can you slow down from -100? Why not?
Temperature scales measure the movement of particles. A particle can only slow down until it stops moving, at that point it can’t go any slower. Like our car that stops moving at -100, particles stop moving at -273 C. Now, if you want a “speedometer” that puts 0 at 0, then instead of Celsius you’d use Kelvin.
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