# Light in Vacuum

1. Jun 16, 2004

### timetraveldude

If you were in a vacuum and shined a flashlight would you see the light?

2. Jun 16, 2004

### The_Thinker

Not unless there are dust particles present or you are shining it at something specific.

3. Jun 17, 2004

You can only ever see light when you look directly at the source or when it is reflected off something....

You can see the sun and stars, and we on Earth are in a vacuum!

4. Jun 17, 2004

### Lokolo

its like the moon, we see the moon only because light from the sun is reflecting off of it onto our earth.

If you shined a torch into space, you wouldn't see the light unless it hits something on its way, and this is delayed (depending on how far away it is!). An example, turn your torch on, a light comes a year later off an object (planet maybe!), switch it off and the light will stop shining a year later.

Ps. you would need a very poweful torch

5. Jun 17, 2004

### 12345

It takes light from the sun 8min. to reach Earth, which means the sunlight you see now set off on it's journey from the sun 8min. ago.

6. Jun 17, 2004

### timetraveldude

This raises some interesting points. If light can only be observed when it is interacting with matter what can be said about its existence when it is not observable?

7. Jun 17, 2004

Absolutely nothing.

8. Jun 17, 2004

### Staff: Mentor

9. Jun 17, 2004

### pallidin

It's existance is not affected. Light, or any other force, does not depend on observation for existance.

10. Jun 17, 2004

### timetraveldude

Just because you can not observe something with your eyes doen't mean you can't say something about it.

11. Jun 17, 2004

### timetraveldude

This is your view. You think that if you can not measure it with a machine or detect it with you senses it doen't exist. You are wrong.

12. Jun 17, 2004

### JasonZ

Noone questioned its existence (except perhaps yourself). Tell us what you believe can be said, since you seem to be looking for a specific (supportive?) answer.

-Jason

13. Jun 18, 2004

### timetraveldude

You people need to learn how to have a debate.

14. Jun 21, 2004

### timetraveldude

Then how do you know it exists?

15. Jun 22, 2004

We are therefore so fortunate to have you here as a fine example.......

I'll obviously have to work on my technique........

16. Jun 22, 2004

### abertram28

how do you know it exists even when you 'see' it? how do you know a blinking light is a blinking light rather than your pulse in a tumor on your optic nerve?

i think you need to re-evaluate your thoughts on knowing and believing. im betting you cant differentiate between the two. most people cant. when they 'see' something they feel that they know it, but really they are believing it. to know it, you must believe in it, true, but you must also know the conditions the predict it and the conditions that it creates. then you can evaluate whether something exists. i believe all science is hypothetical.

17. Jun 22, 2004

### timetraveldude

Because other people see the same thing.

Knowing is certain, believing is not. You know a vase because the mind that perceives the object perceives the object in accordance with the definition of a vase.

18. Jun 22, 2004

### abertram28

the major problem i see with that is that you cannot rule out coinicidence. similarly you cant say that if you dont see it but i do see that it doesnt exist. if its not two way, id say its not proof.

i dont get it. you know why? cause i dont have a definition for vase in my mind. therefore, they simply cannot exist! you said it yourself, if others dont see it, its not really there.

</sarcasm>

19. Jun 22, 2004

### timetraveldude

It is impossible that the number of people who understand red indicates stop is a conincidence.

If you don't understand the definition you don't perceive the vase.