# Probing Question: Are there upper and lower limits to temperature?

##### June 7, 2007 By Steve Miller

Most people have heard absolute zero described as the lowest possible temperature, but what does that mean? Is it really the coldest cold, or just the lowest temperature that we can measure? Is there a corresponding highest temperature? According to Moses Chan, Evan Pugh professor of physics at Penn State, answering these questions requires understanding the meaning of temperature.

"Temperature is a measure of the degree of 'disorder' or 'messiness' of a system," said Chan. "When a system is cooled down to absolute zero, then that system is perfectly ordered and all its constituents -- molecules and atoms -- are in their proper place. That is the lowest possible temperature." Absolute zero, or 0 K (kelvins) corresponds to -273.16 C, or -459.688 F.

Before quantum mechanics was developed as a model to explain the behavior of atomic and subatomic particles, scientists thought that all atoms would stop moving at absolute zero. However, even at this temperature, atoms and molecules retain what is known as zero-point energy, the lowest possible energy a system can have. As Chan explained it, the energy in the vacuum of empty space is considered a form of zero-point energy. Also described as the "ground" or "stationary" state, absolute zero is considered a stable state from which no energy can be removed.

"At low temperatures," Chan continued, "quantum mechanical effects dominate the properties of all matter." In some materials, the effect is truly spectacular. At sufficiently low temperatures, for instance, some types of matter become superconducting, carrying electric current with absolutely no resistance. Practical applications of this phenomena include high magnetic field MRI machines and very efficient electric motors and transformers.

Another vivid example of quantum effects can be found in liquid helium. When liquid helium becomes a superfluid, at temperatures below 2.176K, Chan noted, it can flow without friction. The lack of friction means the superfluid has no viscosity. If a droplet is caused to rotate inside a container, it can continue to rotate forever as if it were in a vacuum. To Chan, these are examples of macroscopic quantum phenomena -- quantum mechanics operating on a macroscopic scale.

Back in the 1920s, physicists Satyendra Bose and Albert Einstein predicted that at very low temperatures particles such as atoms will bunch together at exactly the same lowest energy quantum state. This state of matter is known as a Bose-Einstein Condensate (BEC). The collection of particles acts like a single giant atom. This phenomenon, Chan noted, was finally observed in the laboratory in 1995 by cooling rubidium atoms in the vapor phase down to a temperature of 50 nanokelvins (billionths of a kelvin) above absolute zero. The physicists who observed it, Carl Weiman and Eric Cornell, were awarded a Nobel prize for their work.

Chan's own research at very low temperatures yielded another important breakthrough in 2004. "My former student, Eunseong Kim, found that solid helium also exhibits superfluid-like properties below 0.2K," he explained. "Finding this supersolid phase indicates that all three states of matter -- vapor, liquid and solid -- can undergo BEC." Supersolid phenomena have sparked the interest of low-temperature and theoretical physicists worldwide. Chan and his current students -- Tony Clark, Xi Lin and Josh West -- are continuing the effort to understand this fascinating discovery.

So, is there a high temperature analog to absolute zero? When a material becomes very hot, its particles have lots of thermal energy, Chan said. Solids melt and liquids vaporize because their thermal energy exceeds the forces that bind atoms or molecules together. At even higher temperature, atoms dissociate into electrons and ion plasma, yet another state of matter. As more energy is injected into a system, its temperature continues to rise.

"In the sense that there is a limit to the total energy that exists in the universe, there is a highest possible temperature," said Chan. Cosmologists postulate that at around 10-43 seconds, an unimaginably tiny fraction of an instant after the Big Bang (If you were to take a trip to the farthest galaxy from Earth, 10-43 would represent the first billionth of a millimeter you traveled), the temperature of the newborn universe was 1032 K. Even the center of today's Sun, at 15,000,000 C, is frigid by comparison.

It is clear that we can never harness all the energy in the universe, so the highest possible temperature is not attainable. Can we ever experience the other end of the scale -- absolute zero? "No, we can get very close, but never to absolute zero," said Chan. "Some labs, including David Weiss's here at Penn State, can cool vapor samples to within a few nanokelvins, or billionths of a degree. But to bring something to perfect order, you have to get rid of the disorder or messiness. As the system gets closer to absolute zero, it becomes progressively harder and harder to remove that disorder."

Source: Research Penn State

## Related Stories

#### Promising technique improves hydrogen production of affordable alternative to platinum

October 27, 2015

Scientists have demonstrated that microwaves can help create nanostructured molybdenum disulfide (MoS2) catalysts with an improved ability to produce hydrogen.

#### New hope for terahertz: New laser operates at higher temperatures than some thought possible

December 16, 2010

Terahertz rays -- radiation between microwaves and infrared rays on the electromagnetic spectrum -- are a promising means of detecting explosives, but they've proven hard to generate cost effectively. So far, solid-state ...

#### Understanding the science of solar-based energy: more researchers are better than one

September 2, 2008

View a video of MIT scientists explaining how they recently discovered a catalyst that produces oxygen gas from water.

#### Probing Question: Are we running out of helium?

April 26, 2013

Party planners, take note: the atmosphere may become a little deflated at gala events in the future. Some scientists are sounding the alarm about the wastefulness of using helium—a rare, non-renewable gas—to fill party ...

#### Managing the Internet of Things

May 29, 2015

Researchers in Hong Kong have developed a software platform designed to manage and control devices for "Internet of Things" (IoT) systems. The platform can be tailored for everything from city management sensors and devices ...

#### Study sheds light on prevention of heat stroke for outdoor workers

June 18, 2012

A pioneering study by researchers of The Hong Kong Polytechnic University (PolyU) has shed light on the prevention of heat stroke for outdoor workers in a scientific manner. One of the major recommendations is to link up ...

## Recommended for you

#### 'Material universe' yields surprising new particle

November 25, 2015

An international team of researchers has predicted the existence of a new type of particle called the type-II Weyl fermion in metallic materials. When subjected to a magnetic field, the materials containing the particle act ...

#### CERN collides heavy nuclei at new record high energy

November 25, 2015

The world's most powerful accelerator, the 27 km long Large Hadron Collider (LHC) operating at CERN in Geneva established collisions between lead nuclei, this morning, at the highest energies ever. The LHC has been colliding ...

#### Researchers discover why E. coli move faster in syrup-like fluids than in water

November 25, 2015

Swimming in a pool of syrup would be difficult for most people, but for bacteria like E. coli, it's easier than swimming in water. Scientists have known for decades that these cells move faster and farther in viscoelastic ...

#### Physicists set quantum record by using photons to carry messages from electrons almost 2 kilometers apart

November 25, 2015

Researchers from Stanford have advanced a long-standing problem in quantum physics – how to send "entangled" particles over long distances.

#### Ground-breaking research could challenge underlying principles of physics

November 20, 2015

An international team of physicists, including a Plymouth University academic, has published ground-breaking research on the decay of subatomic particles called kaons – which could change how scientists understand the formation ...

#### Supercomputing the strange difference between matter and antimatter

November 20, 2015

An international team of physicists including theorists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory has published the first calculation of direct "CP" symmetry violation—how the behavior of ...