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Fraser
2007-Mar-12, 03:33 PM
The questions are piling up, so it's time to get through them. We've got a great collection this week. How can our eyes collect so many photons? What's the speed of gravity? ...

Read the full blog entry (http://www.astronomycast.com/questions/episode-27-the-third-question-show/)

EvilEye
2007-Mar-13, 05:38 PM
The very first question on the show created another question for me.

You said "If I throw a rock...."

But that doesn't answer the question of how a photon gets to lightspeed.

My flashlight doesn't have any photons in it that I am aware of. But when I turn it on, there they are, and already going the speed of light. I didn't have to throw them. How to they accelerate from nothing?

Steve Limpus
2007-Mar-19, 10:34 PM
Joao Frasco asked how come he can see a photon stream from a distant star even if he moves just a little to the left or right?

When I thought about his question it made sense if you think of light as particles. Even distributed at Planck distances, as the photons spread out over space you would expect "gaps" to appear between the photon streams at cosmological distances.

Is part of the answer to his question - how come no gaps - to do with the wave properties of light? Doesn't the light also propogate like ripples on a pond in all directions. I'm thinking of the "two-slit experiment."

Can anyone explain better?

EvilEye
2007-Mar-20, 12:24 AM
Oh... and does physics work with a photon?

I mean when a photon IS created and sent on its way, does where it came from experience even the same miniscule reverse reaction?

I mean like a rocket leaving the pad, pushing down on the pad as hard as it is lifting.

Or is a photon independant of Newton's physics?

Steve Limpus
2007-Mar-20, 01:05 AM
Oh... and does physics work with a photon?

I mean when a photon IS created and sent on its way, does where it came from experience even the same miniscule reverse reaction?

I mean like a rocket leaving the pad, pushing down on the pad as hard as it is lifting.

Or is a photon independant of Newton's physics?

Hi EvilEye

I remember something along the line that the photon is "created" by a quantum change to an electron - the electron shuffles orbits back and forth within the atom emitting a photon each time, like when a light bulb filament is heated by electricity.

So the action/reaction exists at the level of energy transfer within the atom. Photons have no mass so perhaps Newtonian physics doesn't apply?

Something like that! :doh:

Steve Limpus
2007-Mar-20, 01:17 AM
Photons have no mass so perhaps Newtonian physics doesn't apply?

Just had a thought - solar sail space craft work off light "pressure" don't they?

There must be some Newtons at work there?