(Phys.org) —Schrödinger's famous thought experiment in which a cat hidden in a box can be both dead and alive at the same time demonstrates the concept of superposition on the macroscopic scale. However, the existence of such "cat states" (or simply "Cats") would be problematic in reality, as cat states not only go against common sense, but also pose problems for understanding gravity and spacetime.

"Different people emphasize different concerns about Cats," Lajos Diósi, a physicist the Wigner Research Center for Physics in Budapest, Hungary, told *Phys.org*. "Some people emphasize different ones at different times. So, allow me to pick up two arguments. Penrose (in my words): A Cat implies superposition of macroscopically different space-times, making physical time elusive. Myself: If we measure a Cat state a la von Neumann (why not?), then the collapse will macroscopically violate many conservation laws."

To address such problems, Diósi has expanded upon a model in which gravity-related spontaneous wave function collapses can suppress Schrödinger cat states, forcing them to take on only one value. Diósi's paper on suppressing cat states is published in a recent issue of the *New Journal of Physics*.

Several years ago, Diósi and Sir Roger Penrose each independently derived a model which can cause the spontaneous collapse of a cat state. This model came to be known as the DP model. According to the model, the measure of "catness" can be quantified as the difference between the two gravitational fields corresponding to the two states that make up a cat state. The greater the catness, the shorter the cat state's decay time.

Traditionally, the DP model is applied to single macroscopic degrees of freedom, such as the center of mass of a macroscopic object. In the new paper, Diósi has for the first time derived the DP model for the acoustic degree of freedom of a macroscopic object. Basically, he shows that macroscopic excitations, or sound waves, vibrating inside a macroscopic object such as a large rock will spontaneously decohere, meaning any acoustic cat states will collapse. The findings open up new perspectives on the concept of macroscopic superposition.

"Spontaneous models are usually thought to influence bodies under extreme isolated conditions [at very cold temperatures]," Diósi said. "I discussed the possibility that the DP model might be significant in common phenomena. I don't mean a directly testable effect in acoustic waves, I mean a first step toward a theoretical search for parametric regimes where spontaneous collapse acts in the common matter of a common state."

**Explore further:**
Micro-macro entangled 'cat states' could one day test quantum gravity

**More information:**
Lajos Diósi. "Gravity-related spontaneous wave function collapse in bulk matter." *New Journal of Physics*. DOI: 10.1088/1367-2630/16/10/105006

## Achille

It is time to stop thinking we should find a way to make this analogy a reality.

## Noumenon

## tritace

Oct 28, 2014## Ducklet

## baudrunner

There was a time when driving at 30 mph was considered reckless, and later that it was simply impossible to travel faster than the speed of sound.

I solidly maintain my status as a practical realist. And yes, this still allows me to believe in the ancient astronaut theory, because all practical analysis points to their being real. Mind-trippers turn the facts into mythical fantasy.

## Noumenon

The point of a "thought experimen" is to remove all of that needless complexity, so as to focus on the point. The cat and poison apparatus is the quantum system.

## arom

Oct 28, 2014## qitana

http://www.youtub...ecUuEqfc

## Whydening Gyre

No, it just adds complexity...

## bee_farms_7

so entropy will kick-in in other words.

(because if the cat is going through time, then he is definitely one or the other = he is either definitely dead or definitely alive --- not both ---- either entropy is there or it isn't --- either time is there or it isn't ---- IF it's a real true alive kitten --- then he is either dead or alive -- not both.

## theon

Measurements will just reveal which ones are alive and which ones not; this eliminates all the hocus-pocus about living-dead cats.

And don't mention the wavefunction of the Universe, the one of my body does not even exist. There is, though, a Gedanken ensemble of myselfs (one real, the other ones in my dreams), just as in classical statistical physics one may imagine an ensemble with Gedanken copies of the macroscopic system one wishes to describe.

## Tachyon8491

## Whydening Gyre

You're not paying close enough attention to the content of the article -

Diosi/Penrose

You need to practice your reading comprehension skills...

## Whydening Gyre

Regardless of the cat's state, he is still THERE....

As are entropy and time...

## Whydening Gyre

The cat's existence is the wave. It's state is the wave function.

I think the Schrodinger analogy is stupid.

Experience via experimentation (Science) has taught us that X time exposure to Y amount of radiation causes death.

Therefore, we know that if that happens, the cat will most assuredly be mostly dead or just plain dead. Just a matter of time...

## antialias_physorg

Since small objects can be described as a wavefunction: what scale limit did you have in mind where such a description is no longer correct?

The point is that we don't know whether it happened (and neither does reality as it's still in a state of superposition of all possible outcomes)

## Da Schneib