Scientists today accept the existence of photons and their weird wave-particle behavior. What they still debate is the more existential side of things, such as where light came from in the first place. To answer this question, physicists turn their attention to the big bang and the few moments that followed.
You might recall that the big bang is the birthing event that gave rise to the universe. You can read more in How the Big Bang Theory Works, but it will be useful to remind you of the basics here. About 15 billion years ago, all matter and energy were bottled up in a small region known as a singularity. In an instant, this single point of super-dense material began to expand at an incredibly rapid rate. As the newborn universe expanded, it began to cool down and become less dense. This allowed more stable particles and photons to form.
Here's what may have happened:
- Immediately after the big bang, electromagnetism didn't exist as an independent force. Instead, it was joined to the weak nuclear force.
- Particles known as B and W bosons also existed at this time.
- When the universe was just 0.00000000001 seconds old, it had cooled enough for electromagnetism to break from the weak nuclear force and for the B and W bosons to combine into photons. The photons mingled freely with quarks, the smallest building blocks of matter.
- When the universe was 0.00001 seconds old, quarks combined to form protons and neutrons.
- When the universe was 0.01 seconds old, protons and neutrons began to organize into atoms.
- Finally, when the universe was the tender age of 380,000 years old, photons broke free, and light streamed across the dark chasms of space.
This light eventually dimmed and reddened until, finally, the nuclear furnaces in stars kicked on and began generating new light. Our sun turned on about 4.6 billion years ago, showering the solar system with photons. Those photons have been streaming to our humble blue planet ever since. A few fell on the eyes of great thinkers -- Newton, Huygens, Einstein -- and caused them to stop, to think and to imagine.
Keep reading for more links to satisfy your curious mind.