[Sephiroth]

Originally Posted by idi banashapan

Imagine the universe like a giant, stretchy balloon with tiny dots drawn on it. These dots represent galaxies.


1. The Universe Expands Like a Balloon

At the very beginning, the universe was tiny, hot, and dense. Then, it started expanding, like blowing up a balloon. The galaxies (dots) weren’t moving through space; instead, space itself was stretching between them.


2. The Light We See Started Its Journey Billions of Years Ago

When we see light from a galaxy that’s 13 billion years old, it means that light left that galaxy 13 billion years ago. But back then, that galaxy was already far away from where we are now, the universe had expanded a lot even by that time.


3. Space Has Stretched the Light on Its Way to Us

Light always travels at the same speed (about 300,000 km per second), but because space itself is expanding, the journey the light had to take got stretched over time. This also makes the light appear redder (this is called redshift). Light moving away appears bluer. This is the light version of a doppler in audio (where an police car siren appears to change frequency and pace as the car approaches and then goes past).


4. The Galaxy Is Much Further Away Now

Even though the light has taken 13 billion years to reach us, the galaxy it came from isn't 13 billion light-years away today. It's much further, maybe 30+ billion light-years away! That’s because space has been expanding the whole time.


So, Why Can We See It?

Even though space was smaller back then, there was already a path for the light to travel. That galaxy wasn’t in the exact spot where we are now, but its light had enough time to reach us as space stretched.


Think of it like this:

If a friend sends you a balloon with a drawing on it, but the balloon inflates while the drawing is traveling to you, the picture still arrives, it just looks stretched out.

That’s what happens to light in our expanding universe!

Thanks for the logical approach - which is how I like it to be.

First, though - a correction: Blue shift occurs when an object is approaching an observer, not receding. Local galaxies might be approaching but expansion of the universe outside any locality is generally accepted due to the red shift observations.

I've got a problem with the balloon analogy where it is stated that the objects on the edge aren't moving - just the space between them. That's not logical to my mind. As the balloon expands, if that's what happening, the objects are moving further from the notional centre. Indeed, the red shift itself indicates relative distance and thus relative motion of the objects being observed.

SO that leaves still with the conundrum that light leaving somewhere close to the centre of the universe that was released closer to the time when the so-called Big Bang occurred and our region of space had not yet been expanded into cannot be seen here! That would knock the Big Bang theory on the head unless it occurred at least 2x the 13.5 billion years that the light we're seeing was emitted.

Plus, relatively, a galaxy on the "other side" of the "balloon" would be even further away and we have no tools with we we could see the so far red-shifted EM waves. It's even been postulated on this thread that such galaxies are receding from us at a speed faster than light itself (hence Einstein's relativity theory).

Logic versus the balloon?