# Alex Filippenko on Reddit (u/AlexFilippenko)

Part of Scientists on Reddit, researched with Autumn (https://www.autumn.ai) from public sources. Updated 2026-11-07. Interactive version: https://www.autumn.ai/resources/scientists-on-reddit/alex-filippenko

Alex Filippenko: Astrophysicist at UC Berkeley, supernova researcher.

- Reddit account: [u/AlexFilippenko](https://www.reddit.com/user/AlexFilippenko/) (Personal account)
- How we know it's theirs: [The 2014 r/IAmA AMA, posted from this account](https://www.reddit.com/r/IAmA/comments/25830r/)
- Where they post, in the records we retrieved: r/IAmA (144), r/space (40), r/Astronomy (1)
- Known activity in the posts we found: 2013 to 2015
- Wikipedia: https://en.wikipedia.org/wiki/Alex_Filippenko

## Moments

### u/AlexFilippenko in r/IAmA, Mar 14, 2013 · Personal story

Replying to a redditor:

> What made you decide astrophysics as a career?

> I've always been fascinated by science. From ages 10 through 17, my main interest
> was chemistry, but as a freshman in high school I was given a small telescope.
> With it, I "discovered" Saturn -- the third "star" at which I pointed the telescope!
> This really jazzed me, and astronomy became a growing interest. In my freshman
> year of college, at the University of California at Santa Barbara, I took an introductory
> astronomy course from Professor Stanton J. Peale, and it was truly wonderful. I realized
> that the physics of the very large is governed by the physics of the very small (atoms
> and subatomic particles), so by switching to astrophysics I could "have it all." So I
> changed majors with the intention of becoming an astrophysicist, and I've never
> regretted the choice.
>
> One final factor in my decision: As a budding young chemist, I played with explosives
> and had a couple of pretty bad accidents. I realized that I don't have the self-discipline
> to stay away from dangerous chemicals, so I should switch fields as an act of
> self-preservation, if nothing else!

Full thread: https://www.reddit.com/r/IAmA/comments/1aaaug/comment/c8vnpku/ · 111 points as of Nov 7, 2026

### u/AlexFilippenko in r/space, Sep 19, 2015 · Explains things

Replying to a redditor:

> Sorry if this is a stupid question, but if space is a vacuum and air naturally gets sucked into a vacuum what keeps our atmosphere from being sucked into outer space? EDIT: added 1 word

> It's actually a misconception that a vacuum exerts a force that "sucks" air into it. Air can spread out from where it is located, into a vacuum if there's one nearby. But Earth's *gravity* keeps the air in our atmosphere from spreading out into space.

Full thread: https://www.reddit.com/r/space/comments/3lkoul/comment/cv777dy/ · 12 points as of Nov 7, 2026

### u/AlexFilippenko in r/IAmA, May 10, 2014 · Explains things

Replying to a redditor:

> Does the fact that the universe is "flat" suggest that we can put a minimum size on the entire universe that's at least as big as a hypothetical closed universe in which or local curvature is too small to detect with current techniques?

> Yes, that's right. I think current estimates place the volume of the entire Universe to be *at least* 80 times the volume of the observable part of our Universe.
>
> But in fact, the entire Universe may well be far, far larger than that, according to inflation models. It could easily be the case that the ratio of the diameter of the entire Universe (all that there is) to the diameter of our observable Universe is as large as the ratio of the diameter of the observable Universe to the diameter of a proton: something like 10^41 for the ratio. In other words, our observable Universe is like a proton relative to the entire Universe. Whoa!

Full thread: https://www.reddit.com/r/IAmA/comments/25830r/comment/chenf7f/ · 56 points as of Nov 7, 2026

### u/AlexFilippenko in r/IAmA, May 10, 2014 · AMA answer

Replying to a redditor:

> Some of my friends have taken your Introduction to Astronomy course at UC Berkeley and loved it. They say that your last lecture is especially inspirational. What do you tell them in that lecture?

> Well, one of the things I tell them is that each of them
> is special in a cosmic sense, not just an insignificant speck
> of dust in the Universe, because they have the intellectual
> capacity to understand what scientists are learning about the
> Universe. In a sense, it's as though the Universe has developed a
> way to know itself, through us. We are the observers of the Universe,
> the explorers of the Universe, the brains and conscience of the
> Universe. And it needn't have been like this! Alter the laws of
> physics ever so slightly, and our Universe may have been stillborn,
> devoid of such complexity. We were dealt a darn good poker hand,
> so to speak.

Full thread: https://www.reddit.com/r/IAmA/comments/25830r/comment/chemd4j/ · 63 points as of Nov 7, 2026