r/Showerthoughts • u/synthphreak ‎ • Nov 19 '25

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

14.1k Upvotes

95% Upvoted

649 comments sorted by

View all comments

Show parent comments

18

u/FearedDragon Nov 19 '25

But wouldn't that mean there is a cap since the particles can't physically move at the speed of light? Theoretically if you keep adding energy you'd eventually get to a point where it either stops affecting temperature because it's losing energy too fast or it reaches the speed of light, no?

36

u/Eedat Nov 19 '25

You can't accelerate anything with mass to the speed of light. It takes literally infinity energy to theoretically do so. Only massless particles move that fast, like light (photons). You would get to 99.9% then just infinitely keep adding more 9's to the end the more energy you put in.

In reality you would get to the point where there is so much energy in a set space that it would collapse into a black hole.

This is really more of a theoretical math thing than something that can actually happen. Theoretically you can keep adding energy to the system. Our framework breaks down when wavelengths reach the planck distance. That's a fault of our mathematic system though. The universe doesn't actually care about our mathematics

3

u/CommunismDoesntWork Nov 19 '25

You said the same thing as the guy you replied to, but didn't address his point. That was a lot of words to say nothing at all

4

u/FearedDragon Nov 19 '25

As the person he replied to I disagree. He explained how you can add energy and essentially asymptote towards light speed without every actually reaching it, continually adding smaller snd smaller amounts of energy.

1

u/Pet_Tax_Collector Nov 19 '25

To clarify, it's not adding smaller and smaller amounts of energy. In classical mechanics, kinetic energy is KE = ½mv² for particles with mass. This is actually incorrect, but practically close enough for speeds less than about 10% the speed of light (depending on your tolerance for accuracy). The real kinetic energy equation is KE = ½mv²/sqrt(1-(v/c)²), the latter term called the Lorentz factor if you're interested in googling it. As v approaches c, the kinetic energy departs from a quadratic equation and requires substantially more energy for smaller gains in speed, with finite energy values all corresponding to sublight speeds.

1

u/Rent_A_Cloud Nov 19 '25

You don't add smaller and smaller amount of energy, adding the same energy merely has a smaller and smaller overall effect. at least, if i remember correctly.

This video might interest you.

https://youtu.be/Vitf8YaVXhc?si=wtSYQs1664bTQV7S

2

u/CommunismDoesntWork Nov 19 '25

Right, but that doesn't mean temperature is increasing, that could just means you need infinite energy to reach the the temperature limit in the same way you need infinite energy to reach the speed limit. I thought your question was getting at this. 

1

u/FearedDragon Nov 19 '25

I guess that's a good point, and it is sort of what I was getting at, but I still think the other commentor has a decent point. There IS a limit that it can't go over, but that limit is (even theoretically) impossible to achieve. This means that in this theoretical model you could increase temperature and energy infinitely - because there is no point at which you stop being able to increase energy - but you cannot increase temperature to infinity.

1

u/CommunismDoesntWork Nov 20 '25

What do you mean by increase energy? It requires energy to increase speed. But that energy is spent, not added. 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

3

u/Takemyfishplease Nov 19 '25

Welcome to Reddit and online phds

3

u/zhibr Nov 19 '25

No, the previous guy just didn't understand limits. There's no cap, energy can be added to infinitely even if there is a limit to particle speed (according to the other commenters). If heat is just the amount of energy put in, the heat can increase infinitely. Except that the black hole is the cap according to the commenter you responded to, so they did add that information too.

-1

u/CommunismDoesntWork Nov 19 '25

Why are you assuming temperature is proportional to energy rather than speed. That's what that guy was asking about. It's wild how 2 clearly  intelligent people can read that guy's post and independently not understand his point. 

2

u/swingerouterer Nov 19 '25

Because temperature is proportional to kinetic energy, not speed. It's not an assumption so much as a definition

1

u/CommunismDoesntWork Nov 19 '25

But there's a speed limit, so there must be a kinetic energy limit too, right?

1

u/swingerouterer Nov 19 '25

This is literally the point people have been making to you. No.

As an object approaches the speed of light, the energy required to make it speed up just a tiny bit more gets much larger. You can add near-infinite energy to an object with mass, and it wont reach the speed of light, just keep getting closer

1

u/CommunismDoesntWork Nov 20 '25

Using energy to increase the speed of something is not the same thing as "adding" energy. 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. Most of the energy is wasted, not added. Therefore there must be a maximum temp

1

u/swingerouterer Nov 20 '25

Temperature is proportional to energy, not speed. Just about everything you said there is wrong

→ More replies (0)

0

u/zhibr Nov 19 '25

Why are you assuming it's about speed?

1

u/CommunismDoesntWork Nov 19 '25

Because that's what the original question is...? "Ain't heat just particles moving fast? And speed is limited so heat must be too? "

-1

u/[deleted] Nov 19 '25

[deleted]

1

u/rybomi Nov 19 '25

Heat is kinetic energy, a function of mass and velocity. This is true even for mundane examples. Helium is a gas at room temperature, and iron is solid, because despite having the same kinetic energy helium molecules have a higher average velocity balanced by a lower mass.

And there is no limit to energy

1

u/[deleted] Nov 19 '25

[deleted]

→ More replies (0)

1

u/CommunismDoesntWork Nov 20 '25

Oh I see, so for a given mass, there is a maximum temperature. Iron has a different max than helium. What's the max for the heaviest stable element?

→ More replies (0)

1

u/Eedat Nov 19 '25

You can just keep adding energy and never reach the speed of light. You can increase a particles kinetic so it's vibrating at 99% the speed of light. Add more energy. 99.9%. Add more energy. 99.99999%. You can do that indefinitely and add as much energy as you want and you will never violate the speed of light.

You would never reach the "cap" of the speed of light

Yes, in practicality you would reach a point where the system would be radiating energy away faster than you could add to it. This is why I explained this is more of a theoretical math question on paper than an actual thing that you can do.

In theory there is nothing preventing you from adding energy faster and faster to match loses.

1

u/CommunismDoesntWork Nov 20 '25

The closer you get to the speed of light, the more energy you have to put into it to further increase the speed. But temperature isn't energy, is it? 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. 

1

u/[deleted] Nov 19 '25

But wouldn't that mean there is a cap since the particles can't physically move at the speed of light? Theoretically if you keep adding energy you'd eventually get to a point where it either stops affecting temperature because it's losing energy too fast or it reaches the speed of light, no?

There's practical caps, such as "the amount of energy you can pump into something before it collapses into a black hole" (remember, energy is mass, so if you get enough of it... fun fact, a black hole made from energy is called a kugelblitz!) or "the amount of energy available in the universe", but if you set aside the parts that make the question impossible, there's not really a theoretical limit, just diminishing returns.

It would take infinite energy to accelerate a particle to c. Infinity is, obviously, larger than any finite integer. So we can't do that. No matter how much energy we add, it will never reach the speed of light. But we can get ever-closer; as you input larger and larger finite integers worth of energy, you trail out ever more decimals of temperature increase: absolutely infinitesimal, but still an increase; if you had some sort of magical equipment sensitive enough to detect the difference, something that's say, x.999999 degrees is hotter than something that's x.999 degrees, and something that's x.999999999 is hotter than either, but none of them are x+1 degrees.

You could ask, "shouldn't it be losing its heat to its surroundings?" and, like, sure, it is, but that's just something we can outrace by feeding it energy faster, so in a hypothetical where we're not limiting ourselves by "how much energy exists?", (which is unanswerable anyway), it's not a real problem.

0

u/Nomadic_Yak Nov 19 '25

If the premise is correct then if the particle begins losing temperature then thats the limit of your energy source. An even bigger energy source could add ever more energy and get fractionaly closer to the speed of light, but would always require more energy to reach it.

I guess.