# What is Coherence? Explained Clearly

• ShayanJ
In summary, coherence is a statistical concept that measures the predictability of results at different times and places based on a single measurement. It is related to interference, where two waves can affect each other if they are coherent. Coherence can occur when waves are traveling in the same direction and in phase, such as in laser beams or light from distant sources.

#### ShayanJ

Gold Member
Recently I've been trying to understand coherence,about waves in general.But its just a little hazy to me.Can someone explain it clearly?
Thanks

This question is asked here repeatedly- have you done any searching?

Coherence is a statistical concept that measures how well you can predict results at other times (temporal coherence) and places (spatial coherence), given a single measurement at your current time and place. The 'mutual coherence function' is the most general expression, 'coherence time' and 'coherence area' are restricted to either the time or space domains. Coherence time depends on the (temporal) frequency bandwidth of the source, coherence area depends on the spatial extent of the source.

Well,I guess I understand that.I'm just confused because people say two waves can interfere if they are coherent with each other or sth like this.But I don't understand why.Interference seems to be a local phenomenon i.e. the amplitude and phase of the waves at one point and only at that point affect the result of their interference but coherence is about the connection of two points,in space or time!

The simplest coherence relationships occur when all of the waves are traveling in the same direction, and are in phase ... just like a platoon of soldiers marching together. Incoherence is a mob running in all directions.

Laser beams have very strong temporal coherence due to the stimulated emission properties: in phase, same energy, and same direction. Light from very distant sources is also coherent: from stars or the sun. This is because all of the incoherence is lost along the way ... imagine an alley at some distance from the rapidly dispersing mob: those who arrive there will all be going in the same direction!

## 1. What is coherence?

Coherence is the quality of being logical, consistent, and understandable. It refers to the clear and understandable connection between ideas, sentences, and paragraphs in a piece of writing or speech.

## 2. How is coherence achieved?

Coherence is achieved by using effective transitions, using consistent and logical organization of ideas, and ensuring that all ideas are relevant and support the main topic or thesis statement.

## 3. Why is coherence important in scientific writing?

Coherence is important in scientific writing because it helps readers understand the research and its findings in a clear and logical manner. It also allows researchers to effectively convey their ideas and arguments in a way that is easy to follow and comprehend.

## 4. What are some common techniques for improving coherence?

Some common techniques for improving coherence include using clear and concise language, using effective transitions between ideas, and ensuring that all ideas are relevant and support the main topic or thesis statement.

## 5. Can coherence be achieved in all types of writing?

Yes, coherence can be achieved in all types of writing, including scientific writing. However, the level of coherence may vary depending on the purpose and audience of the writing. It is important to adapt the level of coherence to the specific needs and expectations of the readers.