# Thread: How far can the sun's light reach?

1. ## How far can the sun's light reach?

If the sun emits a photon towards a galaxy at, say z=2 (what would that be in light years? Anyone got a formula?) would the photon reach a planet in that galaxy before it accelerates over the cosmic "horizon"? What is the cutoff at which it is impossible in principle to reach from the Solar System?

2. The cosmological event horizon is the search term you're after.
It depends on the model of Universe expansion you use, of course. There's a good discussion here, I think.
According to the ΛCDM model, our universe currently is expanding at a rate that increases with time, and our cosmological event horizon is located about 16 billion light-years from us.
(Customary link to Ned Wright's Cosmology Calculator.)

Grant Hutchison

3. I am paraphrasing Tom Mazanec's interesting question, though I already like grant hutchinson's answer:

We see photons from as far out as z=1090 (that's the CMB). We've probably seen a few galaxies from as far out as 12<z<14. But those photons were all emitted when the universe was quite young. If you followed a photon with a free path emitted by the Sun today, How far could it ever get as measured by the material at a z-value we see today? Could it get out to galaxies we see now at z=1?

As grant hutchinson noted, it depends on the model of the universe that you use. I'm curious to know the answer for a few likely models. I suspect Tom needs to know for a story he's writing.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•