Understanding the Disappearance of Light: A Physics Newbie's Question Answered

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Discussion Overview

The discussion revolves around the behavior of light in a closed environment compared to that of water, particularly focusing on why light seems to "disappear" when a door is closed. Participants explore concepts related to absorption, energy transfer, and the nature of light as energy versus matter.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why light disappears from a closed room, comparing it to water, which remains in the room.
  • Another participant explains that light is absorbed by the walls, air, and floor of the room.
  • A different participant adds that while light is absorbed quickly, water is also eventually absorbed, albeit at a slower rate.
  • Further clarification is provided that photons transfer their energy to matter, resulting in a slight increase in temperature of the room.
  • One participant reflects on the nature of light from a falling star, discussing its journey and absorption along the way, while questioning their understanding of the phenomenon.
  • Another participant corrects the previous statement about the timing of light reaching the observer's eye, emphasizing that it is emitted shortly before being seen.
  • A participant distinguishes between light as energy and water as matter, noting that both forms of energy eventually dissipate and are absorbed by the environment.

Areas of Agreement / Disagreement

Participants express various viewpoints on the nature of light and its interaction with matter, with no clear consensus reached regarding the nuances of these interactions.

Contextual Notes

Some participants' statements depend on assumptions about the absorption process and the definitions of energy and matter, which remain unresolved in the discussion.

strmrkt
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Hi, I am new to physics, so this might be a stupid question.

Imagine a pitch black room. If you open the door and shoot water into the room and then close the door, the water will still be in the room.

If you do the same thing, but this time with light instead of water. How come the light disappear from the room when you close the door? Why isn't the photons caught in the room?
 
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The light hits the wall and get absorbed by the wall.
 
strmrkt said:
Hi, I am new to physics, so this might be a stupid question.

Imagine a pitch black room. If you open the door and shoot water into the room and then close the door, the water will still be in the room.
Not forever! Eventually it will be absorbed into the air, floor and walls.

If you do the same thing, but this time with light instead of water. How come the light disappear from the room when you close the door? Why isn't the photons caught in the room?
They are absorbed into the air, floor, and walls, like the water, just much faster.
 
More specifically, when photons encounter matter, they tend to get absorbed, transferring their energy and heating up the matter. So, once the door is closed, the room will be slighter warmer than before. That's where the photons have gone.
 
Interesting thread, "This space for rent" I love that. Good play on words.

I observed a falling star and it appeared seemingly from no where into a long streek and then disapeared. Knowing that this light had traveled a milenia of years to reach my eye and, in this case, that light has a beginning and an end. Or at the very lease saw it end. All of that energy that I saw distiguised was absorbed or as you say the matter around it absorbed it along its way, the energy would be disapated in all directions from its' source. Or am I way off in space, that is rentable, here? :)
 
Robin07 said:
Interesting thread, "This space for rent" I love that. Good play on words.

I observed a falling star and it appeared seemingly from no where into a long streek and then disapeared. Knowing that this light had traveled a milenia of years to reach my eye and, in this case, that light has a beginning and an end. Or at the very lease saw it end. All of that energy that I saw distiguised was absorbed or as you say the matter around it absorbed it along its way, the energy would be disapated in all directions from its' source. Or am I way off in space, that is rentable, here? :)

No, the light that reaches your eyes is emitted a tiny fraction of a second before it hits your eyes.
 
"a falling star" is actually a meteorite that hits the Earth's atmosphere and burns up - only a few hundred km from where you are looking. The short burst of light is only generated a few milliseconds before it reaches you.

The difference between the light entering a room and water, sprayed from a hose, is that the light is just energy and the water is matter. However, the Kinetic Energy (motion) that the water has when sprayed into the room soon dissipates itself and the water will come to a halt so, in both cases, energy soon dies down and is absorbed into the substance of the room (even is the walls don't actually 'absorb' the water).
 

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