I want to know the answer too.

I always thought the universe is expanding to a larger universe. I never thought that it could be expanding to something else.

There's no notion of spacetime outside the universe. The spacetime is the universe.

Two assumptions:

a) the universe is infinite. In this case it doesn't expand into anything, the things inside of it just stretch apart.

b) the universe is finite. In this case it expands into something, but because we're trapped inside spacetime, we can't answer this scientifically.

The wording "expanding" adds more confusion than it helps. See [1] for the discussion about this topic.

[1]: http://curious.astro.cornell.edu/ask-a-question/104-the-univ...

I think it’s like the universe being a balloon (infinite or not) and inflating it. The space between any two points on the balloon increases over time. And at the Big Bang the space was basically 0.

Think of it another way: All matter in the universe is getting smaller. But the universe have the same size, so distances between everything increase.

the universe doesn’t expand into something bigger. It’s like multiplying the set of the real numbers by two, the set doesn’t become bigger and its boundaries do not change.

I think you or someone understands this subject should write a detailed comment in this thread that explains this to software folks like us. I appreciate the help.

I doubt a renowned professor would use expanding instead of inflating. likely the student got stuck on the balloon metaphor.

Explaining what is/was "around" the big-bang was never done properly in most physics courses I've taken, and for a good reason: you need to understand the notion of local space metric before you can get that - as the theory currently stands - there is basically nothing outside of the expanding universe.

There are some things humans will simply never be able to come into contact with or fully comprehend. Such things include the 4th dimension, the concept of infinity, and the concept of nothingness. The universe and what lies outside of it, unfortunately involves all of these concepts, so while there may or not be nothing beyond the universe, because we cannot measure this or engage with this, it is only effectively nothing and not literally nothing.

Is the universe infinite? Debatable.

What’s the answer? Curious.

It's not expanding, separate points are growing further apart.

Any metaphor you hear about a balloon or fabric or things like that is an overly simplified version of complicated mathematical models of the universe.

Are electrons getting larger? Are atoms getting larger?

Long story short, no and that's because forces are only applicable in certain situations and not others, and in this case gravity, electromagnetism, and similar subatomic forces are binding the atoms we know and preventing them from "expanding". I'm not an expert and this is just my simplified version of a simplified version.

Here's more to read about it:

https://www.quora.com/Astrophysics-If-the-universe-is-expand...

https://medium.com/starts-with-a-bang/ask-ethan-if-the-unive...