Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

How many observers would it take to cancel out the number of photons produced in a medium sized star like our Sun, thus making it dark?

(I want to consume more photons than the star is generating)

share|improve this question
1  
It depends how close they are to the sun and on how large each is (in a non-overlapping sense) –  Henry Oct 23 '12 at 20:52
    
Is there a way to even begin to calculate such a thing? Let's go smaller... how about a candle flame? What would it take in terms of consumption to render a candle dark? –  aserwin Oct 23 '12 at 22:36
2  
What in the world do you mean by "observers"? Would a black sphere surrounding the star count as an observer? That would make it dark... –  FrankH Oct 23 '12 at 23:32
add comment

1 Answer

up vote 2 down vote accepted

It is certainly true that observation of a photon destroys it. However the energy of the photon has to go somewhere, and it usually goes into heating up the observer.

Suppose you surrounded the Sun with a complete sphere of observers, then very quickly the shell of observers would heat up to the same temperature of the Sun and would start emitting photons itself. Then result would be that distant observers would still see the same net radiation coming from the Sun.

In a sense this already happens. The energy the Sun produces is generated by a relatively small part of the Sun near its centre. The rest of the Sun absorbs photons heading outwards then emits photons in turn. It takes energy emitted from the core at least 100,000 years to escape from the surface. I say "at least" because estimates of the energy travel time vary widely. Anyhow, if you count the outer layers of the Sun as "observers" then the process you describe already happens.

share|improve this answer
    
It would be the same net energy but if the sphere of "observers" has a very large radius compared to the radius of the sun, the photons would be much lower energy per photon and thus there would be more photons. –  FrankH Oct 24 '12 at 6:58
1  
I specifically avoided talking about photons because they're a widely misunderstood concept. I'd say a photon is best viewed as the unit of interaction of the photon field. The view of light as a swarm of photons is misleading. –  John Rennie Oct 24 '12 at 7:33
1  
OK about photons. But the impression I got from your answer is that the black sphere would end up being as bright as the Sun but it wouldn't since it would be infrared rather than visible light. in the Sun gamma ray photons in the core the core become visible photons at the surface. –  FrankH Oct 24 '12 at 11:44
    
The temperature of the sphere would depend how far above the Sun's surface it was. If it was co-incident with the surface it would be at the same temperature as the surface. The further away the sphere is the colder it will be. –  John Rennie Oct 24 '12 at 13:52
    
Exactly! So mention that in your answer. Otherwise it sounds like it would be the same as the sun. –  FrankH Oct 24 '12 at 15:20
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.