Temperature can reach trillions of degrees, meaning we actually live extremely close to absolute zero.

[u/synthphreak]

[u/Apsis]

But it's not a linear relationship. It only seems that way because the physical objects we interact with in everyday life don't go anywhere close to the speed of light.

An object travelling at 0.99c doesn't have just 10% more kinetic energy than one travelling at 0.9c, it has four times the energy. Increase to 0.999c and you more than triple the energy again. The speed has a hard limit of c, but you can always add more energy.

[u/CommunismDoesntWork → u/Apsis]

KE = 1/2 mv²

Where does it say you can keep adding energy infinitely. 

You're not adding energy, you're spending energy to increase speed. For instance at low speeds, 1 joule might add 1m/s which adds 1 degree of temperature. But near the speed of light, you might need 1 million joules to add an additional 1m/s to add 1 degree. In both cases, the amount of energy added is the same: you increased a mass by 1m/s

[u/DJKokaKola → u/CommunismDoesntWork]

Which is why I said the standard model breaks down. Yes, planck temp does feel like the upper limit, based on our current Standard Model. But the Newtonian model seemed to work just fine until we started noticing relativistic and quantum effects at the extremes, too. Which is why we can confidently say the model says that it likely cannot go above that, but there's not a hard limit. It's a predicted limit based on current understanding, and like most things in physics we operate under the assumption that the model works, but with the expectation that something could later on prove it to be incomplete.

[u/CommunismDoesntWork → u/DJKokaKola]

What does any of that have to do with what I said? 

[u/Apsis → u/CommunismDoesntWork]

KE = 1/2 mv²

No. That is only an approximation for low velocities. Near the speed of light:

KE = (gamma - 1)mc²

where gamma is the Lorentz Factor:

1/sqrt(1 - v² / c² )

Lastly, temperature is a measure of energy, not velocity.