# Why isn't there light exiting anywhere else?

• yosimba2000
In summary, this video explains the behavior of light passing through a block of plastic with changing density. The light takes the path with the least time to arrive at the current exit, rather than taking another path to exit at a different point. This is due to Snell's Law, which explains why light is refracted at a certain angle and not others. Unlike a regular light bulb, which emits light in all directions, a laser produces light in a narrow beam, resulting in only a small amount of light emerging at a wide angle.
yosimba2000
In this video, a laser is being shined through a block of plastic with changing density.

At time 0:13, light enters the plastic and exits. The light takes the path the way it does because that path provides the least time to arrive at the current exit

But why doesn't the laser also take another path to arrive at another exit below the current exit? Surely there is ANOTHER path of least time that would allow light to exit at another position?

I imagine that instead of a laser we use a lightbulb, the whole block of plastic would be illuminated and each possible exit point would have light passing through it. What's up with a laser?

OmCheeto
In the end, you're asking why, when a ray of light enters water, it gets refracted at a certain angle, not at others. That's essentially Snell's Law, so I would recommend reading that.

Yes, I know of Snell's Law, but what I'm confused about is why the light doesn't get reflected everywhere to cover all possible points.

If I shine a regular lightbulb through a piece of plastic, all possible exit points on the other side of the plastic are illuminated. Not so with the laser, as shown in the video.

The laser can only produce light in one direction?

yosimba2000 said:
If I shine a regular lightbulb through a piece of plastic, all possible exit points on the other side of the plastic are illuminated. Not so with the laser, as shown in the video.

The laser can only produce light in one direction?

The intensity of light from a laser is almost entirely contained within a thin beam than only slowly spreads out as the light travels. Only a very small amount of light emerges at a wide angle from the laser. This is unlike a regular light bulb where light is being emitted in every direction from each point on the surface of the filament (or phosphor coating if we're talking about fluorescent lights).

davenn

## 1. Why is space considered to be dark if there are stars and galaxies?

The reason space appears dark is because it is mostly empty and does not contain any significant sources of light. While stars and galaxies do emit light, they are extremely far apart from each other, resulting in large gaps of darkness in between. Additionally, the light from these objects can only travel so far before it becomes too faint to be detected by our eyes.

## 2. If space is mostly empty, why isn't it completely dark?

Despite the vast emptiness of space, it is not completely dark due to a phenomenon called cosmic microwave background radiation. This is a faint glow of light that permeates the entire universe and is leftover from the Big Bang. It is believed to be the oldest light in the universe and is the reason why space has a very low level of light, rather than being completely dark.

## 3. Why does light not travel infinitely through space?

Light travels in a straight line and can only travel so far before it becomes too faint to be detected. This is because light is a form of electromagnetic radiation, which can be absorbed or scattered by particles in space. The farther light travels, the more it interacts with these particles, causing it to lose energy and become less visible.

## 4. How do scientists know that there are areas in space without any light?

Scientists use various methods to detect and study light in space, such as telescopes and satellites. By analyzing the wavelengths of light and the amount of light received from different regions in space, scientists can determine the presence or absence of light in those areas. Additionally, the absence of light is also inferred from the lack of visible objects or structures in those regions.

## 5. Could there be other forms of light in space that we cannot see?

Yes, it is possible that there are other forms of light in space that we cannot see. The electromagnetic spectrum includes a wide range of wavelengths, and visible light is only a small portion of it. There could be other types of light, such as infrared or ultraviolet, that we are not able to detect with our eyes, but can be observed using specialized equipment. Additionally, there could be forms of light that are completely unknown to us, waiting to be discovered by future scientific advancements.

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