# Looking for an explanation/definition of a "causal diamond"

• Jimster41
In summary, the conversation discusses the concept of a "causal diamond," which is a representation of a computation with an input and output. This is used to explain the idea that for any experiment or computation, there is a starting point and an endpoint. This concept is related to the idea of an observer's birth and death, with the diamond's surface acting as a horizon for the observer. The conversation also mentions the association of temperature with the non-eternal observer.
Jimster41
hopefully something a little better than the wiki etc. What does a "deformed" one look like, or one drawn in the case of EPR, entanglement etc.

Scott Aaronson has an explanation http://www.scottaaronson.com/democritus/lec20.html with a picture of the causal diamond.

"Bousso formalizes this notion with what he calls a "causal diamond," but I'd just call it a computation with an input and an output. The idea is you have some starting point P and some endpoint Q, and then you look at the intersection of the forward light-cone of P and the past light-cone of Q. That's a causal diamond. The idea is that for any experiment we could actually perform—any computation we could actually do—we're going to have to have some starting point of the experiment, and some end point where you collect the data (read the output). What's relevant isn't the total amount of entropy in the universe, but just the total amount of entropy that can be contained in one of these causal diamonds."

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If P and Q are the birth and the death of the observer, the diamond's surface is an horizon for him. He will follow a line which cannot skip behind this horizon.
Even if there is no acceleration,Roveli writes that a temperature has to be associated to this non eternal observer.
If you see no thermal bath it is because you are eternal!

Jimster41

## What is a causal diamond and how is it defined?

A causal diamond is a concept in physics that represents a region of spacetime that is bounded by two null surfaces, typically representing the past and future light cones of a given event. It is defined as the intersection of two light cones that originate from a single point in spacetime.

## What is the significance of a causal diamond in understanding causality?

Causal diamonds are important because they provide a way to visualize and understand the relationships between cause and effect in a given spacetime. They allow us to see how a single event can have ripple effects in both the past and future, and how the actions of one object can impact the surrounding environment.

## How is a causal diamond used in theoretical physics?

In theoretical physics, causal diamonds are often used as a tool for studying the effects of quantum entanglement and the concept of the "block universe." They are also used in the study of black holes and the nature of time in general relativity.

## Can causal diamonds be applied to real-world situations?

While the concept of a causal diamond is primarily used in theoretical physics, it can also be applied to real-world situations, such as predicting the spread of diseases or analyzing historical events. However, the accuracy of these applications may vary depending on the complexity and accuracy of the underlying model.

## Are there any controversies or criticisms surrounding the use of causal diamonds?

Some physicists argue that the concept of a causal diamond is limited in its ability to fully capture the complexity of causality in the universe. Others question the validity of using a single point of origin to define a causal diamond, as it may not accurately represent the true nature of causality in a given spacetime.

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