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Sibling rivalry doesn’t always show up in ways you expect.

One aspiring physicist has spent years building his identity around a single passion, planning an entire future in astronomy and physics.

So when his sister announced she’s studying applied physics too, that sense of ownership started to crack. Logically, he knows she hasn’t done anything wrong and he wants her to succeed.

But knowing that doesn’t stop the discomfort of imagining a future where “the physics sibling” isn’t a title he holds alone anymore.

You’ll want to keep reading for this one.

AITA for feeling weird that my sister wants to study physics too?

I (18M) have been interested in astronomy and physics for a long time.

I am studying physics right now and I want to become a physicist and hopefully work in astronomy one day.

So one day, when his sister also showed interest in the subject, it pushed him over the edge.

Recently, my sister said she’s planning to study applied physics.

I don’t think she’s doing anything wrong, and I genuinely want her to succeed.

The problem is that I feel strangely uncomfortable about it.

He starts to feel like she’s somehow encroaching on his identity.

Part of it is that I always felt like physics was my thing.

It feels awkward imagining us both being “the physics siblings,” getting compared by family, or having our careers overlap.

He recognizes this isn’t exactly logical, but it doesn’t change his feelings.

I haven’t argued with her about it because I know these feelings might be irrational.

I don’t want to stop her from studying physics, and I don’t think she should change her plans because of me.

I just can’t shake the feeling that something I considered uniquely mine suddenly isn’t anymore.

AITA for feeling this way?

Is an entire subject really something this teen can take ownership of?

Redditors really rip the bandaid off with their feedback.

This teen hasn’t really done anything wrong — yet, anyway.

Maybe he should take this as more of a compliment than an insult.

Gatekeeping is never the right move.

If you enjoyed this post, check out this story about a student who did the math and figured out he was better off skipping school than serving detention if he forgot his ID.

Wanting something to stay “yours” isn’t the same as wanting someone else to fail. Those two things can exist in the same head without making anyone the villain.

This isn’t really about physics. It’s about identity, and how much of that identity got built around being the only one in the family chasing this particular dream.

Clearly expecting his sister to study a different subject isn’t the right path forward, but it’s still good to acknowledge his feelings so he can begin to plot a more productive path forward.

Building a stronger sense of identity is always a great exercise, and it looks like he found the perfect catalyst.