Why do we use infinity in Physics?

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Discussion Overview

The discussion revolves around the use of the concept of "infinity" in physics, particularly in relation to simplifying complex problems and making assumptions about distances in various contexts such as black holes and electric fields. Participants explore the implications of using "infinity" versus other terms like "some place far away" or a specific distance.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the necessity of using "infinity" when discussing distances in physics, suggesting that a distance `x` could suffice.
  • Another participant argues that "infinity" is a convenient shorthand for discussing limits as distances become very large, despite being a simplification.
  • Some participants propose that using "infinity" allows for the omission of complex parameters in problems, such as when calculating the electric field of a charged object.
  • It is noted that "some place far away" can be misleading, as it may not always imply a significant distance, and can sometimes refer to very small distances.
  • In optics, the use of "light coming from infinity" is explained as a way to assume that light rays are parallel, which simplifies analysis.
  • A mathematical perspective is introduced, where "tending to infinity" is used to describe behavior in exponential equations without providing finite figures.

Areas of Agreement / Disagreement

Participants express a range of views on the appropriateness and implications of using "infinity" in physics. There is no clear consensus, as some advocate for its use while others suggest alternatives or highlight potential misunderstandings.

Contextual Notes

The discussion highlights the limitations of terminology in physics and the potential for misunderstanding when using terms like "infinity" or "some place far away." The nuances of these terms depend on the specific context of the problem being addressed.

Phys12
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When we talk about a particular problem in Physics. For instance, let's say that light is coming from somewhere to hit the earth. We often say that the light is coming from "infinity." Let's say that we're tackling a black hole and we have a person somewhere as an example and we say that let's say that the person is at "infinity."

My question: why "infinity"? Can't we say that it's at a distance `x` that we don't know, or some place far away? Why "infinity"?
 
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It would be more accurate to say "in the limit approached as the distance becomes arbitrarily large", but that's a mouthful. Especially in informal discussions, it's easier to say "infinity" and move on.
 
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you can say that it's at a distance `x` that we don't know. but for a lot of problems you want to omit parameters that make the solution complicated, for example if you want to find the electric field of a charged iron chair, it's may be very difficult... but if you say that you are in the "infinity" you can omit the changes in the surface of the chair and treat it like a single point charge.

"some place far away" - it's more accurate than "`x` that we don't know" but misleading... some times "some place far away" is only 1 micro-meter away. "after a very long time" can be just a second and so on

"infinity" it's just terminology for "you can omit the annoying stuffs from your equation" ;)
 
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EnEE said:
you can say that it's at a distance `x` that we don't know. but for a lot of problems you want to omit parameters that make the solution complicated, for example if you want to find the electric field of a charged iron chair, it's may be very difficult... but if you say that you are in the "infinity" you can omit the changes in the surface of the chair and treat it like a single point charge.

"some place far away" - it's more accurate than "`x` that we don't know" but misleading... some times "some place far away" is only 1 micro-meter away. "after a very long time" can be just a second and so on

"infinity" it's just terminology for "you can omit the annoying stuffs from your equation" ;)
Perfect! :D

Thank you.
 
In optics, light coming from infinity is shorthand for the assumption that the light rays are perfectly parallel. For any x less than infinity, the rays radiate out at an angle relative to each other.

Infinity sounds far fetched, but parallel seems simple and ordinary.
 
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In mathematics we talk about an exponential equation tending to infinity as it slides right on the X axis. getting closer to y=0 and North on the Y axis as it tend to X=0. As we do not offer a finite figure we use the term tending to infinity.
 

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