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FQXI ARTICLE

May 23, 2022

The End of the Quantum Road?

Caslav Brukner ponders whether we’ve already found the ultimate theory of nature, without realizing it.

FQXi Awardees: Caslav Brukner

September 23, 2011

CASLAV BRUKNER

University of Vienna

Kuhn’s influence has been profound—and it’s left some wondering whether physicists will ever find the much sought after

In the video below, Brunker talks about classes of theories that may move beyond quantum theory, and whether the next theory will be crazier than quantum:

The germ of Brukner’s obsession with quantum theory goes back to his childhood. Born in Novi Sad, Serbia, in 1967, the young Brukner was always more interested in asking "why?" rather than "how?". He recalls being more excited about pondering the nature of time and what makes a watch tick, rather than taking it apart and putting it back together again. When his brother gave him a copy of

"Over the years, I have learned that quantum physics is weird and eludes every attempt to be understood within a classical picture," says Brukner. "It is this weirdness that keeps my curiosity alive—like that of a child— and searching for answers to nature’s puzzles."

Brukner is now searching for those answers with the help of a $69,600 grant from the Foundational Questions Institute. At the heart of his research is the question of whether quantum physics provides the ultimate description of reality or whether there are other more fundamental theories lying in wait.

It is this weirdness

that keeps my curiosity

alive—like that of

a child.

that keeps my curiosity

alive—like that of

a child.

- Caslav Brukner

Some physicists find this quantum weirdness hard to stomach and hope to retrieve a classical concept of realism in which properties of the world about us exist regardless of whether or not we observe them. Einstein famously believed that particles contain extra properties, or

Quantum Overload

Brukner began to examine the features of quantum mechanics when he moved to Austria to pursue a Ph.D. at the Vienna University of Technology with Anton Zeilinger. Together, they realized that many weird quantum features could be explained by thinking about the information contained in a quantum system, just as computer scientists look at how information is encoded, stored, and transferred in bits. According to their approach to quantum mechanics, the most elementary quantum system, the qubit, carries one bit of information.

QUANTUM CROSSROADS

Should we accept quantum mechanics as the ultimate theory?

Or keep looking?

Credit: IQOQI, University of Vienna

Brukner argues that the total information that can be carried by an electron spin is finite. That means, by necessity, the system’s answers to some questions will contain an element of randomness. Thus, Brukner and Zeilinger realized that the observed quantum behavior could be explained by nothing more mysterious than a lack of storage space for sufficient information.

One of the most

exciting questions for

physicists is: what

is our next theory?

exciting questions for

physicists is: what

is our next theory?

- Caslav Brukner

Brukner and Zeilinger have analyzed how information can be stored in an entangled system. For example, it would take two bits of information to jointly encode entanglement into two particle spins, so that they are parallel to each other. Once those two bits have been exhausted, there is no more storage space to encode extra spin information into either of the two entangled particles individually, says Brukner. As a result of this lack of extra encoded information, measuring the spin of one of the pair must yield a random value, while the spin of its partner will be immediately fixed, regardless of distance.

Final Theory?

Brukner’s work suggests that weird quantum properties such as superposition and randomness are here to stay—any theory that tries to get rid of them will fail to overcome this information limit. So, does that mean that quantum theory is the final theory? Should we now stop hunting for anything deeper? Not necessarily.

"One of the most exciting questions for physicists is: what is our next theory?" says Brukner. "The entire history of science has taught us accepted scientific theories are superseded by new ones, of which the old are special cases. It is therefore hard to believe that quantum theory is our final theory."

Although most proposed alternatives to standard quantum mechanics have steadily fallen by the wayside, Brukner believes that this is because they all tried—mathematically and conceptually—to save some part of the pre-quantum concepts of classical physics. Brukner, however, wants to study alternatives that preserve the seemingly bizarre properties of quantum mechanics. "I want to investigate those theories, which, like quantum theory, are intrinsically probabilistic, allow superposition and entanglement, but may still differ

Brukner is a very

deep thinker, who

believes in fundamental

connections between physics

and information.

deep thinker, who

believes in fundamental

connections between physics

and information.

- Vlatko Vedral

Vlatko Vedral, a quantum physicist at the University of Leeds, UK, likes Brukner’s attempts to derive theories beyond quantum mechanics. "Brukner is a very deep thinker, who believes in fundamental connections between physics and information," says Vedral. "Herein lies the hope to go beyond speculation and arrive at some experimentally testable predictions, which is the main goal of physics and underpins its wonderful power to comprehend the world."

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Please read the important Introduction that governs your participation in this community. Inappropriate language will not be tolerated and posts containing such language will be deleted. Otherwise, this is a free speech Forum and all are welcome!

Recent Comments

MARCEL-MARIE LEBEL wrote on October 10, 2011

LC

At the speed of light, time stops. Then, a true time duration can be found as the period T of an EM wave.

On the other hand, the wave (assumed as being of the same nature) associated with a sub-luminal speed particle does not experience stopped time and therefore does not have a true per se period T. This variable T does not exist for the free associated wave. But when we interact with the particle, we cause a slight deceleration and the emergence of a wavelength and period T....

LC

At the speed of light, time stops. Then, a true time duration can be found as the period T of an EM wave.

On the other hand, the wave (assumed as being of the same nature) associated with a sub-luminal speed particle does not experience stopped time and therefore does not have a true per se period T. This variable T does not exist for the free associated wave. But when we interact with the particle, we cause a slight deceleration and the emergence of a wavelength and period T....

LAWRENCE B. CROWELL wrote on October 10, 2011

The “box” or infinite well is a potential which enters into the Hamiltonian. A measurement process is something which is commonly thought of as outside the system. Now one can introduce some quantum system which entangles with the system you are measuring. However, there is this chain of observations, for this process does not reduce the wave function, but rather replaces the superposition of states with an entanglement. There must then be some additional detection of the entangled state...

The “box” or infinite well is a potential which enters into the Hamiltonian. A measurement process is something which is commonly thought of as outside the system. Now one can introduce some quantum system which entangles with the system you are measuring. However, there is this chain of observations, for this process does not reduce the wave function, but rather replaces the superposition of states with an entanglement. There must then be some additional detection of the entangled state...

MARCEL-MARIE LEBEL wrote on October 9, 2011

LC

Or, maybe you understood it almost right. Be it Stern-Gerlach or Zeeman or any other measurement, measurement applies an additional constraint which comes to be one more and last quantum number. The measurement is making it quantized. Same as a particle in a box; constraint is forcing the temporary quantization.

Marcel,

LC

Or, maybe you understood it almost right. Be it Stern-Gerlach or Zeeman or any other measurement, measurement applies an additional constraint which comes to be one more and last quantum number. The measurement is making it quantized. Same as a particle in a box; constraint is forcing the temporary quantization.

Marcel,

read all article comments