Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Temperature Limit
Name: TJ
Status: student
Age: 20s

Location: N/A
Country: N/A
Date: 2000-2001

There was a question posted some time ago regarding the upper limit of temperature. The answer given was that there is no limit to temperature beacuse it is a measure of the average kinetic energy of particles,but what if the average kinetic energy of those particles approached the speed of light (natures speed limit according to the theory of relativity) wouldn't the temperature eventually reach an enormous yet FINITE limit, as the kinetic energy of the particles approached, but could not exceed, the speed of light?

The speed of light does not limit the kinetic energy of particles. In the usual way of looking at it, as you approach the speed of light the amount of energy required to go faster increases without limit.

However, the argument relating temperature to kinetic energy is gounded in nonrelativistic physics, and there are other ways of looking at temperature. In statistical mechanics, you look at the number of different states available to a bunch of particles, and temperature describes how this number changes as the total energy increases. From this view, temperature can even be negative, so there certainly is the possibility of a maximum temperature.

Tim Mooney

The kinetic energy has two components: mass and velocity. As velocities approach the speed of light the mass starts to increase, thus requiring more energy to continue to accelerate the object. While the speed of light limits the velocity, the mass can increase indefinitely, thus the kinetic energy continues to increase.


No, there is no upper limit. While there is a finite limit to the velocity the particles may travel at (the speed of light), the kinetic energy may in fact become infinitely large.

At low speeds, the kinetic energy may be approximated by the equation:

K = 0.5 * m * v * v

However, at near light speeds, the correct equation should be used:

K = m * c * c * (1 / (sqrt(1-(v/c)*(v/c)) - 1))

In this equation, as v becomes closer to c, the speed of light, the equation approaches infinity. When v = c, the exact value is undefined since 1 is divided by 0, but it is some infinitely large number.

Basically, think of it this way, kinetic energy depends on the velocity and mass of the particle. As the speed of the particle approaches the speed of light, the mass of the particle also increases until it is infinitely large.

At low speeds, the change in mass is so small it is largely ignored and has no noticeable effect on the results. However, at near light speeds, just the opposite occurs. The change in velocity is less important to the final result than the change in mass.

Eric Tolman,
Computer Scientist

Speed and kinetic energy are related, but they are not the same thing. It is incorrect and in fact misleading to think of the kinetic energy of an object approaching the speed of light.

Although it is true that no object with mass can travel at the speed of light, that doesn't mean that there is an upper limit to an object's kinetic energy. This is because an object's mass increases as it travels faster. In fact, by the theory of relativity, an object traveling at the speed of light would have infinite mass. In terms of kinetic energy, what this means is that the kinetic energy of an object, given by the formula mv^2, increases faster than just the square of the velocity. As v approaches c, m approaches infinity, and so does the kinetic energy.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory