Why can't we see the light before we turn on the bulb?

  • Thread starter Jonnyb42
  • Start date
  • Tags
    Bulb Light
In summary, the conversation discusses the concept of the "light cone" and a question about why we cannot see light from a light bulb before it is turned on. The answer is that the light only emits in the future direction, and events outside the "light cone" are not connected to the light bulb.
  • #1
Jonnyb42
186
0
Pardon me if there is an obvious answer, I have not spent too much time thinking about it.

Having stumbled upon the "light cone." (Just the spacetime diagram centered around the event of turning on a light source.) I have the following question:

I am not going to be too detailed, but why can't see the light from a light bulb we switched on before we switched it on, if the light emits in the past direction as well as the future direction?
 
Physics news on Phys.org
  • #2
It does not emit in the past direction.

Only events within the past light cone can affect the light. Anything outside the light cone is causally unconnected to the light bulb.
 

1. Why can't we see the light before we turn on the bulb?

The light from a bulb is produced by a flow of electrons through a filament, which creates heat and light. When the bulb is not turned on, there is no flow of electrons and thus no production of light. Therefore, we are unable to see the light before the bulb is turned on.

2. How does the bulb produce light?

The bulb produces light through a process called incandescence, where an electric current is passed through a filament, causing it to heat up and emit light. This process is similar to how the sun produces light through nuclear fusion.

3. Can we see the light from a bulb in complete darkness?

No, we cannot see the light from a bulb in complete darkness because light requires a medium to travel through. In complete darkness, there is no medium for the light to travel through, so it cannot reach our eyes for us to see it.

4. Why does the bulb take a few seconds to produce light after being turned on?

When a bulb is turned on, it takes a few seconds for the filament to heat up to the point where it starts producing light. This is because the filament has to reach a high enough temperature to emit light, and this process takes a few seconds.

5. What is the difference between incandescent and LED bulbs?

Incandescent bulbs produce light through the process of incandescence, where an electric current is passed through a filament. On the other hand, LED bulbs produce light through a process called electroluminescence, where a current is passed through a semiconductor material, causing it to emit light. LED bulbs are more energy-efficient and have a longer lifespan compared to incandescent bulbs.

Similar threads

B Can We "See" Effect Before Its Cause?
    • Special and General Relativity
Replies
11
Views
1K
I Understanding Simultaneity Through Male & Female Clocks Meeting
    • Special and General Relativity
Replies
12
Views
1K
I Michelson & Morley in Space-Time Diagram: Can't Make it Work
    • Special and General Relativity
Replies
18
Views
1K
I Solving the Flickering Light Paradox
    • Special and General Relativity
Replies
20
Views
1K
Why do the headlights on the car become dim when the car is starting?
    • Introductory Physics Homework Help
Replies
4
Views
266
I Understanding Relativity of Simultaneity in Resnick, Part II
    • Special and General Relativity
Replies
20
Views
803
I How to Measure Speed of Light & Is It Constant?
    • Special and General Relativity
Replies
13
Views
1K
B Why does it require an infinite amount of energy to reach the speed of light?
    • Special and General Relativity
4
Replies
130
Views
8K
Can RGB LED simulate incandescent bulb 'glow'?
    • Electrical Engineering
Replies
3
Views
1K
I Why doesn't relativity of simultaneity lead to a contradiction?
    • Special and General Relativity
Replies
17
Views
576

Hot Threads

Recent Insights

Back
Top