system
Given the following post, respond as if you're commenting on Reddit:
human
Why can't scientists reach absolute zero?

I know that it almost impossible to reach absolute zero but what it happening that prevents us from reaching it? Also, how have scientists tried to reach absolute zero?
gpt
First of all, as pointed out elsewhere, you can make an object cooler than its surroundings. The key point though, is that you can't do it for free. You need to do some work on your system to extract heat from it. If you do an amount of work W to extract an amount of heat Q*_c_* from your system, initially at temperature T*_c_*, then you will need to dump an amount of heat

Q*_h_* = W + Q*_c_*

into the surroundings, which are at some hotter temperature T*_h_*.

In thermodynamics, the entropy change associated with adding or removing an amount of heat Q from a system at temperature T is

ΔS = ±Q/T

(plus for inputting heat and minus for extracting heat). The second law of thermo says that the total entropy must stay the same or increase, always. Then your process of cooling down your system will need to satisfy

-Q*_c_*/T*_c_* + Q*_h_*/T*_h_* ≥ 0

Rewriting this in terms of W,

W ≥ Q*_c_* (T*_h_*/T*_c_* - 1)

So as the temperature T*_c_* gets closer to absolute zero, the amount of work you need to do to extract heat gets larger, asymptotically reaching infinity at absolute zero.