They knew waaaay more than the rest of us did at the time, you don't wanna get MeToo'd for a party you went to 100 years ago, do you?

The temporal trolley problem. Lol

There's a few of these

I think the biggest one for me is quite how much support Hitler apparently had in the Anglosphere before the wars.

Assuming he managed to grow that support without war, I have a feeling we would have potentially had a very fascist 50s across the world instead of the era of progressive politics we actually got. Then whatever inevitable revolution or nuclear winter that followed a couple of decades later, would leave the world looking very different to today.

Right I think if some bloke brought me some OG plague from the 1200s, my body would have no clue.

I think chirality is something most people overlook in those situations too. Even if you found a world of beings exactly like you, a perfect earth with plants and low CO2 concentrations, if their proteins have opposite chirality to yours, you’re probably going to die of prion disease.

“Oh look a perfectly human person on an earth like planet I’m sure I can take my helmet off”. Nope. You just inhaled spores or skin cells or pollen or viruses or literally anything that contains “misfolded proteins” and if any of those get at all digested they could cause your body to produce more misfolded proteins, a cycle that will eventually lead to your demise.

“Look this plant isn’t poisonous” chirality is harder to check than chemical makeup. So yeah it has vitamin B but is it the kind that could kill you? (We don’t have to worry about this much on earth because basically all life on this planet makes and uses proteins of similar chirality)

“Wow that alien sex was great” too bad there were skin cells in saliva you both exchanged/ingested (or proteins in other bodily fluids) so you’re both going to die now.

Worst part is that prions are really slow acting. You could all be chilling in this wonderful earth like home for months until around the same time you all suddenly get sick and die. There’s no cure, so there’s nothing you can do besides leave a warning for the next crew who might stop by.

Oh and the same dangers go for native life on the planet too. To them you’re made of misfolded proteins so any scavengers who eat you and maybe even predators who eat them have a chance of developing and spreading prion disease. Your bodies are basically bioweapons. Any earth crops or animals you brought with would be biohazards too.

I personally trust humanity that we will work out a way to have sex with something we shouldn't rather quickly. Our horniest scientiest and our brightest perverts will find a way, even if it's at great personal cost.

There's a decent chance one or both species carries some form of microscopic life that the other has no defenses against

I'd argue there's essentially zero change we'd be biologically similar enough for any microbes to bridge the gap. It's a big deal when microbes jump species here on earth

Not only will starship captains and crew not be able to have sex with the hot aliens they meet

Not so fast, we do have some convenient barrier device to avoid contamination in this context.

Can you explain more about the last sentence how planets with oxygen might be the most dangerous please? I'm interested

Sounds like philosophy of identity. What is you? Is only things with your DNA you? Will a bunch of dead hair, skin cells, and nails teleport with you? Are the things inside your body you? Is only your brain you and it will get transplanted into a new body in the future?

The time traveler's diarrhea

There was already an outbreak of thousand year old Anthrax from thawed animal corpses in Siberia several years ago.

Or any smallpox samples sitting in the back of an old lab, like the ones they found in 2014. Or the smallpox samples that the US and Russian governments keep ~~as WMDs~~ for research purposes.

You're just knowledgeable enough to know that Earth moves, but not intelligent enough to know that there's no absolute reference frame it moves in respect to.

If you don't continue travelling with the Earth along its path when you time travel, you could literally end up at any random point in the universe, unless you pick a different, arbitrary, body to move in reference to.

Lol, like the people time traveling wouldn't be able to shift the absolute position in space....

People say this but the reality is that you are already traveling through time and you aren't teleporting into the space where the Earth used to be. Just as traveling backward would essentially just reverse that process. i.e unless you specifically design a time travel device to kill you that way, thats not how time travel works.