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Light tends to spread out as it goes, so we only see a little bit of what originally started out the further away we are.

Photons also get absorbed by gasses and dust in their path too, which also causes it to fade.

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Hi Mick. Not a daft question at all. Photons move through free space at the speed of light. They do not deviate from a straight line, or slow or stop, unless something interferes with their progress.

I have a question. How can I understand what a photon is? I understand its an elementary particle described as a quanta, or 'package', of energy which is a type of EM radiation acting as a wave as wel

http://www.amazon.com/QED-Strange-Theory-Light-Matter/dp/0691024170 will tell you everything you want to know and you will understand it.

Just rereading my answer. It's not true that light spreads out as it travels as such, a photon will follow a perfectly straight path at all times (subject to GR and so on).

It's just that for a light source such as a torch or even a laser, the photons are not all travelling perfectly parallel to each other. So over larger and larger distances, those that are just a little bit away from parallel will diverge.

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Just reading this produced this odd thought.

If light produces photons, and photons travel at the speed of light and never die, they will eventually cross the universe.

For the past 130ish years, earth has been getting brighter due to the use of electric lights in increasing numbers. So much so, that many of our major cities are visible from space. In fact you could say that earth no longer has a dark side. So might it be reasonable to assume that some alien being on a distant planet in the future, will observe this phenomenon and conclude that the earth is (a) inhabited (B) getting hotter © going to explode

Or maybe all three. :Envy:

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Radio waves do not decay in outer space. We are still in communication with the Voyager space craft that left the solar system almost 15 years ago. It's radio is equivalent to an in car CB radio. Eventually the signals become part of the background noise of the universe, but their still there

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Just reading this produced this odd thought.

If light produces photons, and photons travel at the speed of light and never die, they will eventually cross the universe.

Light is photons. Photons can die, that's what seeing is, the absorption of photons, which turn into electrical signals - either in the eye, CCD or just any old electron somewhere.

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If we're talking individual photons then yes, they go on forever, until they impinge on something. However, light beams, behave in the same way as radio transmissions, following the inverse square law...

The chances are you'd not detect any of the photons arriving at the moon, as they'd been absorbed in the atmosphere, but if we assume that some get through, then you should be able to detect them on the moon.

Confucius say, if photon travel and not interact with any body for all eternity, does photon exist? What is sound of one hand clapping when tree falls in the forest and monk is asleep?

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I have a question. How can I understand what a photon is?

I understand its an elementary particle described as a quanta, or 'package', of energy which is a type of EM radiation acting as a wave as well as a particle? If it has no mass how can I get my mind to comprehend what a single package of a wave is and how it physically moves and interacts with 'stuff'?

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I have a question. How can I understand what a photon is?

I understand its an elementary particle described as a quanta, or 'package', of energy which is a type of EM radiation acting as a wave as well as a particle? If it has no mass how can I get my mind to comprehend what a single package of a wave is and how it physically moves and interacts with 'stuff'?

http://www.amazon.com/QED-Strange-Theory-Light-Matter/dp/0691024170

will tell you everything you want to know and you will understand it.

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