Hey folks! Here’s a pinned post where you can ask science questions!
Here’s a quick rundown of what this post is and isn’t:
- This is a place where you can ask science-related questions!
- This is a place to provide science-based answers to others’ questions!
- This isn’t reddit’s askscience community. By this I mean we don’t have the resources (or, really, desire) to vet users’ credentials, and you shouldn’t expect that whoever is answering your question is necessarily an expert. That said, this community does have a large share of professional scientists and engineers, and I’m hoping that those folks will be interested in sharing their expertise when they can.
- This isn’t a place to ask for medical advice – since we can’t vet qualifications these kinds of questions won’t be allowed here in the interest of preventing harm, and I’ll remove any comments that ask personal medical questions. If you have a question about medicine that’s not asking for advice, that is fine and allowed.
- This isn’t the only place on this community where you’re allowed to ask questions! If you have a question related to another post, ask in the comments there. If you have a question not related to another post, I’d like it if you tried asking here first (to help this thread gain some traction), but you’re also free to ask in a separate post if you’d prefer (or both).
I’m going to post this inaugural thread with no set expiration date. I’m currently thinking a new thread maybe every 2–4 weeks, but I’d like to see what the volume of comments here ends up being like before deciding for sure.
I’ll start us off with a biology question:
One thing I’ve always been really interested in is biomineralization, especially as it relates to single-celled organisms like diatoms and magnetotactic bacteria. But it seems like moving solid crystalline materials around inside a cell (or from the inside out, I assume, in the case of diatoms?) would be much more difficult than moving around liquids or bendy organic molecules. How do cells manage to do this?
It’s probably formed outside the cell, with some extracellular matrix nucleating the crystal which is then built from ions pumped out by transport proteins.
In humans you can compare cartilage with bone. Cartilage is mostly organic extracellular matrix, where bone simply adds deposited calcium carbonate in between the extracellular matrix (where the water would be in cartilage).
Thanks for the reply! Does the idea of an extracellular matrix make sense for single celled organisms like diatoms?
I’m not a biologist but I do research with “mineral” types of materials. It does indeed seem much more difficult to transport solids than liquids within the cell. But from what I know cells have organelles called vesicles to move things around, and nanoparticles are plenty small to fit inside them. With some brief searching I found this article https://www.nature.com/articles/s41467-021-24944-6 that shows the process in diatoms using cryogenic transmission electron microscopy. So they imaged this process directly. They actually found that this species deposits the silica directly into the cell wall. So for long thin structures they do transport the Si-compounds in liquid. I’m sure you can find further reading in this article’s references.
Ooh fascinating! Starring this post for later when I’ve got a moment to look at that paper. As a TEM guy myself (although I’ve never done cryo), it’ll be really interesting to see their figures! Thank you for sharing, I’m excited to have a look!
Got a physics question everyone. Or maybe it’s more of a sanity check? Can someone explain to me the relationship between entropy and relativity? I’ve been reading about entropy and how it is one of our theories, if not the only, that is tied to the arrow of time, with most or all of our other theories working regardless of time’s direction. My understanding is that this has led some to consider that the probabilistic functioning of entropy creates our subjective experience of the arrow of time, despite relativity seeming to inform us that all spacetime already exists as a 4D manifold.
But I’m struggling to conceptualize that in combination with relativity, or even come up with good questions to understand what it is I am struggling with lol. Maybe this is it: If entropy creates our subjective experience of moving along the arrow of time, that would still make sense with relativity, right? Because any entropy related to me is in my frame of reference, whether I am moving at just below the speed of light or I’m affected by this planet’s gravity? And this is what we see with particle accelerators as well - that radioactive particles with certain half-lives will have extended half-lives relative to an observer’s frame of reference outside the accelerator.
I guess I am also struggling with what your question is! I think I’m getting hung up on: “Because any entropy related to me is in my frame of reference…” What exactly is it you mean by this? I think the source of confusion is probably coming from here, since as far as I can tell the rest of what you said makes sense.
(Also, just to clarify a point: there’s no issue with time being a dimension and the arrow of time also being a thing. The arrow of time arises from the boundary conditions on time, ie the low entropy state of the early universe, and it’s totally okay to have dimensions that are bounded at one or both ends. For example, if you’re standing on an infinite plane in a 3D space, one of your space dimensions is also bounded on one side. The plane forms a lower boundary on the up-down dimension, but you could travel up as far as you want.)
Okay so, it’s common for people to talk about distant stars as appearing one way because the light takes (mi|bi)illions of years to get to us, and that makes perfect sense to me… But when they go on to say that, for instance, Betelgeuse has already gone supernova but we won’t see it until the light gets to us…
According to the principle of the relativity of simultaneity, since the speed of light is the speed of causality, wouldn’t it be a bit more accurate (though definitely more confusing to the public) to say that the stars actually are as we observe them, but that the star is far enough away that traveling to it, even instantly, would basically require significant time travel forward? I guess it would just be a different way to talk about “the present” in relativistic terms, which is only difficult because our languages never evolved to handle the concept.
What you think?