Hey! Is achieving absolute zero possible? And how? What would the implications be?

No, you can not get to absolute zero. To get to absolute zero, you would have to remove all of the energy (excluding zero point energy, which can not be removed) from the system. But to do that, you need to keep energy from getting into the system as you are removing it from the system. Since the greater universe (everything that is not part of the system you want to cool) is not at absolute zero, it will always be trying to warm your system up. The only way to keep the flow of energy from the greater universe from getting into your system is to perfectly isolate the system from the greater universe. But there is no way to perfectly isolate a system from the greater universe. So no matter how hard you try to isolate the system as you are cooling it, there will always be some coupling to the greater universe that will be adding energy, trying to thermalize the system and you will never be able to remove all the energy in the face of this always-on heating mechanism.

But you can get awfully close. Refrigerator technologies (such as dilution refrigerators) can get down to around 0.001 K. Laser cooling can be used to cool clouds of atoms or single atoms down to 0.000001 K. Laser cooling is actually a number of different techniques each with different cooling limits, but the basic idea is that you couple your atoms to a laser. If you think of something that is very cold, it has a very small distributions of states. The colder it is, the smaller the distribution of states. A laser is coherent light with a single (or very very close to a single) state of light. So by coupling the laser to the atom, you can use the laser to interact with the atom to leave it in a smaller distribution of states, while the laser light absorbs the atom's lost state distribution. Thus the laser can reduce the atom's state distribution and cool the atom. Laser cooling and similar techniques can also be used on things like mirrors and cantilevers (physical objects) to cool them, but the temperature limits of these larger objects are not nearly as low as they can be for atoms. The coldest things we can make are Bose-Einstein Condensates (and also cold Fermi gasses). A Bose-Einstein Condensate, or a BEC for short, is a collection of atoms that is super cold. To make a BEC you start out with a cloud of atoms and laser cool them to the coldest possible laser-cooling temperature. Then you trap the atoms in a magnetic trap and you slowly reduce the strenght of the magnetic trapping until the atoms are just barely trapped. That allows the hotest atoms (the ones travelling the fastest) to escape from the trap. By continuing to slowly lower the trap depth, you will eventually be left with the coldest atoms. This is called evaporative cooling because it is nearly identical to the way a cup of coffee cools down as it evaporates (the hotest atoms escape, leaving only the cold ones). By doing this, you can cool the atom cloud down to 0.0000001 K or less, at which point the atoms condense into a "new state of matter" that behaves differently than normal matter. This is about as cold as we can make things, but still it is not absolute zero.

You should know that absolute zero is not just the lowest kinetic energy. It is the lowest energy in general. Often people think temperature is a measure of how fast the atoms are moving, but there are other degrees of freedom that an atom can have energy in. Atoms can be excited into higher electron states. In thermal equilibrium, the electron states and the motional states and all the degrees of freedom will have the same amount of energy. So to get to absolute zero, you not only need to slow the motion of the atoms, but you need to remove energy from the electron states and any other possible states.

You should also know that in some definitions of temperature, you can actually have negative temperatures. Lasers are such an example, as you can legitimately attribute a negative temperature to a laser. But by other definitions, a laser would have an infinite temperature. So it depends on exactly how you define temperature.

Achieving Absolute Zero

In real practice, if you want to measure something, you will somehow affect the something you are trying to measure right?

So, if you are trying to measure the energy of something with zero KE, how do you do it. If you shined a photon on it, you just imparted momentum to it right?

Now let's say you don't impart any momentum to it, you wait for it to send something to you by radioactive decay. If it sent something to you, it will have imparted a reactive force to itself in the opposite direction. Even if it was capable of simultaneous equal and opposite decay release, it will cause an elastic oscillation.

These are just a couple of thoughts.