# At what temperature do the laws of physics break down?

I heard that as approaching the temperature of a kugelblitz the laws of physics break down, I saw this in the video The Kugelblitz: A Black Hole Made From Light, by SciSchow Space.

• At the planck scale: T ~ m_P c^2/k_B
– Ihle
Jul 8, 2017 at 21:39
• Which laws? There's several different models of physics, which break down at different points. Jul 9, 2017 at 0:52
• The laws of physics never break down. What happens is that the weakness in our models become obvious. Jul 9, 2017 at 3:58
• @EvilSnack: The "laws" are our phrasing of our models. The behaviour of nature never breaks down. Jul 9, 2017 at 11:32
• Our laws of physics (the ones that appear in academic papers, on Wikipedia, and everywhere else) may break down but you can bet that the laws of physics (that we don't actually know) do not. Jul 9, 2017 at 22:56

Hank Green is describing the concept of the Planck temperature, $$T_\mathrm{P} = \sqrt{\frac{\hbar c^5}{Gk_B^2}}\approx1.4\times 10^{32}\:\mathrm K,$$ which is defined as $\frac{1}{k_B}$ times the Planck energy $E_\mathrm{P}=\sqrt{\hbar c^5/G}\approx 1.9\times 10^{9}\:\mathrm J$.

As with all the Planck units, we don't really know what happens at those scales, but we're pretty sure that the laws of physics as we know them are likely to require modifications to continue describing nature at some point before you reach that regime.

What doesn't happen at the Planck scale is that "the laws of physics break down", which is a meaningless catchphrase that shouldn't be used. Unless, in fact, the world changes so much that there is no regularity to physical phenomena and no way to predict how an experiment will pan out, even in principle, then what you have is not a breakdown of the laws of physics, it's just that you've left the region of validity of the laws you know, and you need to figure out what the laws are on the broader regime.

• To further emphasize, not only do you need to figure out what the laws are in the broader regime, you need to do so in a way that still reproduces all the current laws (now viewed as approximations of the broader laws) in their regime, and probably with a smooth transition between the two. That is, we need to explain why we were ever confused by the "wrong" laws. We can do this even for Aristotle's physics, which is to say Aristotle's model does work in its regime. Jul 9, 2017 at 0:45
• The subtle link in the previous comment is an excellent read, highly relevant and pleasant to boot. I recommend clicking.
– FvD
Jul 9, 2017 at 16:10
• I'm accustomed to hearing "The laws of physics break down at T = 0." Do you hear a problem with that? Jul 10, 2017 at 3:26
• @Joshua You've likely misheard that. If you have a concrete occurrence with more context, it can probably be posted separately. Jul 10, 2017 at 7:12

Adding to @Emilio's answer, what happens during Planck's temperature is unknown. Our laws of physics does not seem to work at that temperature(@EvilSnack) for e.g. gravitational force. At that temperature, gravitational force seems to become as strong as other fundamental forces like electromagnetic forces, strong and weak nuclear forces leading to research in quantum nature of gravitational forces. On the Wikipedia article of Planck's temperature:

At temperatures greater than or equal to $\mathrm{T_P}$, current physical theory breaks down because we lack a theory of quantum gravity.

This statement is explained in details in this site:

The Planck temperature is the highest temperature in conventional physics because conventional physics breaks down at that temperature. Above $\mathrm{10^{32}~K}$, Planck time-calculations show that strange things, unknown things, begin to happen to space and time. Theory predicts that particle energies become so large that the gravitational forces between them become as strong as any other forces. That is, gravity and the other three fundamental forces of the universe—electromagnetism and the strong and weak nuclear forces—become a single unified force. Knowing how that happens, the so-called "theory of everything," is the holy grail of theoretical physics today.

"We do not know enough about the quantum nature of gravitation even to speculate intelligently about the history of the universe before this time," writes Nobel laureate Steven Weinberg about this up-against-a-brick-wall instant in his book The First Three Minutes. "Thus, whatever other veils may have been lifted, there is one veil, at a temperature of $\mathrm{10^{32}~K}$, that still obscures our view of the earliest times." Until someone comes up with a widely accepted quantum theory of gravity, the Planck temperature, for conventional physicists like Steven Weinberg, will remain the highest temperature.

Basically, if $\mathrm{0~K}$ is absolute cold that Planck's temperature is absolute hot(i.e a body cannot get any hotter than Planck's temperature).

• No, you've missed the point of the sources you quote. There's nothing stopping bodies from getting hotter than the Planck temperature. We just don't know what will happen if they do. Jul 9, 2017 at 11:33