# Light Behaviour at High Speed: Explained

• B
• Daveopg
In summary, the conversation discusses the concept of relativity and how there is no such thing as "moving fast" as it is all relative to something else. It is also mentioned that an object with mass cannot travel at the speed of light. The question asks about the angle of a light beam when moving at different speeds, but it is pointed out that this is dependent on the frame of reference and there is no absolute angle.
Daveopg
First, I am way out of my field of understanding here so please keep it simple. I watched some videos on E=MC2 which led to how light reacts differently than matter at high speeds causing time to slow down when moving fast.
My question is, if I was to shine a flashlight perpendicular (90 degrees) to the direction traveled am I correct to say if I was moving at half the speed of light the beam would actually be at a 45 degree angle and when traveling at the speed of light the beam would be horizontal (0 degrees). This would also be true whether the beam was inside or outside of the spacecraft , correct?

The most important thing to realize is that there's no such thing as "moving fast". You can always regard yourself as stationary, and there is no experiment that will say differently. You can only be moving fast or slow relative to something else, so all of the relativistic effects you read about are things I determine happen to you and you determine happen to me, but we never directly experience them ourselves. So "light reacts differently than matter at high speeds" doesn't make any sense. Nor does it make sense to talk of whether the light beam is "actually" moving at one angle or another - there's only your description and mine. Both are equally valid.

Secondly, it's contradictory to talk of an object with mass traveling at the speed of light. It cannot happen.

However, you have your question more or less right. If you shine a laser perpendicular to what I would call your direction of motion then I will say that the beam keeps up with you (you won't see anything unusual). But if you are doing 0.5c I must measure the beam at 60° (not 45°) to your direction of travel, so that its velocity is c and the component parallel to your direction of travel (##c\cos 60##) is 0.5c.

Last edited:
Daveopg said:
My question is, if I was to shine a flashlight perpendicular (90 degrees) to the direction traveled am I correct to say if I was moving at half the speed of light the beam would actually be at a 45 degree angle and ...
Unwittingly you've assumed an absolute frame of reference here. There's no such thing as "actually" moving at a 45 degree angle. Your trigonometry might be not quite right either.

For example, at what speed and in which direction are you moving now? Relative to your computer, the centre of the Earth, the Sun, the centre of the galaxy, the Andromeda galaxy ...?

cianfa72 and Ibix

## 1. What is the speed of light?

The speed of light is approximately 299,792,458 meters per second in a vacuum.

## 2. How does light behave at high speeds?

At high speeds, light behaves as both a wave and a particle, known as a photon. This is known as wave-particle duality.

## 3. How does the speed of light affect time and distance?

According to Einstein's theory of relativity, the speed of light is constant and does not change. This means that time and distance can appear to be different for an observer moving at high speeds compared to an observer at rest.

## 4. Can anything travel faster than the speed of light?

According to current scientific understanding, nothing can travel faster than the speed of light. This is known as the cosmic speed limit.

## 5. How does light behave in different mediums?

Light can travel at different speeds in different mediums, such as air, water, or glass. This is due to the varying densities and properties of these mediums, which can cause light to refract or bend.

• Special and General Relativity
Replies
18
Views
1K
• Special and General Relativity
Replies
51
Views
3K
• Special and General Relativity
Replies
45
Views
3K
• Special and General Relativity
Replies
2
Views
467
• Special and General Relativity
Replies
25
Views
3K
• Special and General Relativity
Replies
25
Views
1K
• Special and General Relativity
Replies
45
Views
3K
• Special and General Relativity
Replies
130
Views
8K
• Special and General Relativity
Replies
1
Views
707
• Special and General Relativity
Replies
38
Views
3K