That planet you’re orbiting may look familiar, but how can you be sure it’s the one you left behind? After all, whether you’re getting around with hyperspace, subspace, or something more exotic entirely, you’re leaving the normal universe, with its well understood physical laws, behind. If even the slightest thing goes wrong (or right), you might find yourself in a world both unsettlingly alien and uncomfortably close to home. Alternate universes, where your closest friends are dire enemies or the human race has succumb to tyranny. The rules of these places may go against everything you’ve fought for, but it’s hard enough to save one universe–to try to set things right in all the infinite universes is a task not even Sisyphus would envy.

No, the best you can hope for is to get home (which, if you ask Dr. Sam Beckett, is easier said than done), and here are some of the ways to make sure that happens.

4. What Could Have Been

Some of the worlds you come across will make you really appreciate what you have, though.

What? No, not those articles. The idea’s the same, though: an alternate universe offers you a window into things that never happened in your home realm, and another season of your favorite show is only the tip of the iceberg. If you end up passing through more than one alternate universe, you’ll have the opportunity to see events unfolding in dozens of ways you might never have thought possible–different outcomes of elections, different victors of wars… some of these worlds might seem practically utopian compared to your home dimension.

One of the more insidious consequences of visiting other universes is a “grass is greener” effect. Every time anything goes poorly, it would be easy to find yourself thinking, “I bet things went better back there.” And even if they didn’t, there’s some universe where they did, right? No matter how unlikely it is, there’s at least one reality where it happened. It’s just a matter of getting there…

3. The Allure of the Lost

No matter how familiar they look, they’ll never be who you want them to be.

Perhaps worse than the hunt for a perfect world is simply the siren song of that which you’ve already lost. Whether it’s a critical battle that turned the tide of war, or a loved one cut down in their prime, there’s a universe out there where it never happened. You can have them back, and without any risks of destroying the timeline!

But not really. They might look like the person you knew, but they aren’t. No matter how similar their universe might seem, you can’t account for all the tiny differences; how can you reminisce about a memory you shared when it was raining in their universe that day but sunny in yours? And that’s assuming the similarities are more than superficial, which is extremely hard to prove–you could wind up having brought over their evil goatee-faced counterpart who will make it their new goal to foil you at every turn. (Everyone knows that mirror universe counterparts have a goatee, even if it’s just on their heart.)

If, somehow, it all goes perfectly, and the quantum winds align, even that may not be enough to sway the nagging doubt inside. Every once in a while, out of the corner of your eye, you’ll see the stranger they always were and remember the truth. Just hope there’s no afterlife where you’ll have to explain this.

2. Another Self

Sometimes it’s just a paint job.

Your friends, enemies, and loved ones won’t be alone in having duplicates across the multiverse–the odds are good that you might just run into an alternate version of yourself, also. Perhaps unsurprisingly, this typically doesn’t go well. Being faced with one’s self might highlight insecurities and force you to realize what it’s really like for other people to deal with you… but hey, it might be a good excuse for some character development, right?

On the other hand, you might also run into a version of yourself that has none of those flaws you’ve always been worrying about. The alternate you that’s competent, confident, and unflinchingly courageous, one that never suffered that great failure which you struggle to make up for. Is this the greatness you might have been destined for if you hadn’t been such a screw-up? No one can make you feel more inferior than yourself, after all.

But even those alternates are a blessing compared to some of the ones you might see. The tortured soul that’s lost everything… the coward who faltered at a critical junction… the monster who crossed the line and did the unthinkable without hesitation. These mirrors have many reflections, so a word of warning to those who gaze upon themselves too intensely.

1. Matter Exchange

The stars are going out? No, that happened a long, long time ago. They’ll never shine again.

But hey, there are reasons not to mess with alternate realities aside from emotional damage. For example, have you ever heard theories about the end of the universe? No, you probably won’t cause your universe to collapse instantly upon leaving, but…

Scientists speculate that there are two ways the universe could end: the “Big Crunch” and the “Big Freeze.” All space and matter in our reality was launched outward from a single point in the Big Bang, leading the universe to constantly expand from the beginning of time until now. In a Big Crunch scenario, the combined forces of gravity from the matter cause this expansion to slow, and eventually reverse, pulling everything back inward to a single point, and potentially restarting with a new Big Bang. The Big Freeze, on the other hand, never manages to slow down that expansion, causing everything to spread further and further apart, until the universe becomes a uniform density and temperature. No new Big Bang, just nothing. Forever.

Did you catch the key difference between those scenarios? The amount of matter present being sufficient to reverse expansion is key. Normally that’s a fixed constant, but you and your universe hopping antics have caused a little problem. The constant flow of matter has upset that precious balance, and shifted us from a Crunch to a Freeze, effectively destroying any hopes of continued existence for your home dimension. You never hear this discussed, because it’s usually pretty small amounts of molecules moving from one to another–lungs full of air, a piece that falls off a spaceship… but overtime, this builds up, and we’ve got billions of years to the end for it to do so.

Good job breaking the Universe!

I guess that’s it for this week. Any other tips for those daring to enter another universe? You can leave them in the comments below.