epidemiology

Yeah but equally that original plague bacterium has no clue about antibiotics and no resistances. So you'll be fine. As probably will be people in the Future. Or they died out without you anyway.

The guy who speaks with a computer that reads his cheek movements is probably a good candidate for falling under "celebrities they flew in to provide a smoke screen."

I feel safe in assuming Hawking wasn't actually tied into an oligarchal pedophile conspiracy.

I often wonder how different the world would be if Hitler had used his power for good.

what about water in your cells? checking out the pyramids being built and showing up as a mummy? maybe tying time travel to biology is a bad idea

You time travel and are suddenly both very hungry and a little more bald, haha.

The Ship of Timeus

Prion diseases are not as simple as coming into contact with a protein composed of D-amino acids.

While it's still not fully known, it's generally one specific type of protein PrP^C that gets transformed by PrP^Sc, converting the C to Sc, and so on.

D-amino acids also occur naturally on earth.

As for B vitamins, none include proteins as far as I remember, they're all small(ish) molecules like biotin and folate. Also having a difference in stereochemistry with most of these vitamins, wouldn't cause toxicity.

Obviously there are some cases of small stereochemical changes being toxic (thalidomide). But generally small changes won't automatically make something toxic.

Prions wouldn't work like that. They would have to be very similar, and the same chirality, as our own proteins, or else the misfold would not self-replicate like prion diseases do.

Obligatory "that Venn diagram is basically a circle."

Yeah, it is probably going to be one of the top 5 reasons to join a starship crew, so life will probably, ah, find a way. For all we know, NASA might even have a focus group working on this already.

BUT that doesn't mean it won't lead to the extinction of one or both species involved.

Read "scientities"

That's the result of a balance between different microbes and their own defensive measures. Entirely novel microbes and biological functions could overwhelm all of that. Hell, if they have just evolved a next level ATP, they could have access to an order of magnitude more energy than our microbes and bodies can use, in which case we'd probably have no chance unless it doesn't recognize us as food.

It's not guaranteed to happen, but with 0 data about alternate evolution trees, any reasoning about the odds is speculation (including my use of "decent chance").

Edit: This would be the case for viruses. Unless they work very differently or our biochemistry has some convergent evolutions, alien viruses should be harmless to us and vice versa. Just like the hundreds of viruses we are exposed to with every breath, most don't react to our cells any differently from how they'd react to wet rocks.

I guess it's possible to have safe alien sex with a full body latex suit and respirator. Though maybe think twice if the alien has sharp spike features.

Oxygen is reactive enough that free O2 doesn't tend to stay that way. Even to us, too much oxygen is toxic because it starts reacting with things we don't want it to inside our bodies (which is why antioxidants are beneficial). The presence of oxygen in an atmosphere implies there's life producing it (or maybe some other process we aren't yet aware of). It can also imply that there's also life using it to keep it in a balance that doesn't freeze the planet or allow it to destroy any life because oxygen producers keep pumping more of it into the atmosphere.

And the danger part comes from a combination of alien life maybe having microbes our immune systems can't defend against and the possibly of picking one of those up and bringing it back to other human settlements before the carriers realize they have a fatal infection.

That second part is what makes it more dangerous than a ship accidentally flying into a star or trying to land on a gas giant, which would probably be fatal to all aboard the ship but not dangerous to humanity as a whole. Even just entering an oxygen atmosphere with a ship that never lands could be bad if that ship must later return home.

But the universe is also constantly expanding. So the frame of reference becomes obsolete because it's at an entirely different point in space now.

Throw thousands of satellites back in time but each offset. Measure when you get a broadcast from them and how far back you sent them and bam, we find out for reals.

Then there's you who forgot that we actually do have a universal reference frame with the cosmic microwave background.

Nah, I know the thing with reference points, but that's a matter of navigation and relativity.

In reality, a point in space is a point in space, like, a specific "pixel" of the Universe (oversimplified) that might be occupied with something or not.

We just can't anchor this point since we don't know what reference is absolute and the laws of physics can be applied to every inertial reference, so this doesn't help.

hey I invented time travel, but there's one thing I can't figure out... how do you travel in space?

I think a time travel device would, itself, need to be a spaceship anyway. And since it would have to travel FTL to achieve time travel in the first place, getting back to where Earth is at that point in time shouldn't be difficult.

If your time machine works this way, if you're not isolated from reality while you travel, you'll have to do everything at crazy speeds and potentially backwards and you'll be limited by the age at which you're reasonable enough to be able to travel back. You won't be able to travel to times when you don't exist as a person.

Nope, actual Earth.

That thing that gets routinely ignored by every starship captain ever?