Short Answers To Big Questions: What Is Dark Matter?
ARI SHAPIRO, HOST:
Time now for short answers to big questions. A while back, we asked you to challenge astrophysicist and NPR blogger Adam Frank with your questions about physics, astronomy or science in general. You did. And Adam Frank is here with some answers. Hi, there.
ADAM FRANK, BYLINE: Great to be back.
SHAPIRO: All right. Today's question comes from Randall Russell (ph). He tweeted to ask how the search for dark matter is going, asking, what are the prevailing theories? Adam, first remind us what dark matter is.
FRANK: Right now, when we think of dark matter, we think of it as, like, a cloud of invisible particles, right? So it's definitely - it's a particle...
SHAPIRO: Do you mean literally invisible, or just not detectable by, like, a telescope?
FRANK: Here's the cool thing. It's literally invisible in the sense that - like, you know, when you put your hand on the table, why does your hand stop, right? It's because the matter in the particle and the matter in your hand are interacting right there, exerting forces on each other so your hand doesn't just pass through the table.
FRANK: But these dark-matter particles barely interact with everything else, right? So right now right - if there is dark matter, right now there is a stream of dark-matter particles passing through you. And they're like ghosts in a sense. They just barely ever interact with any other kind of matter except through gravity, which is actually pretty weak.
SHAPIRO: Wait. So we're not just talking about stuff that's light-years away. We're talking about stuff that is here now...
FRANK: Oh, yeah.
SHAPIRO: ...On Earth...
FRANK: If dark matter...
SHAPIRO: ...Around us?
FRANK: If dark matter exists - so the way to think of it - there's a - you know, think about the galaxy. We think of the galaxy as being this beautiful pinwheel sort of thing. If dark matter's true, that's not the galaxy. The actual galaxy is this giant ball of particles, this giant gas of dark-matter particles. And that's where most of the matter is, right? The irony of dark matter and dark energy is most of the universe seems to be in this dark, invisible, non-interactable - or barely interactable - form.
SHAPIRO: But, ultimately, it sounds like the answer to the question, how goes the search for dark matter, is pretty much the way it's been going, which is that there's no real progress.
FRANK: When it comes to the direct detection, yeah, there's no real progress. We're doing lots of interesting studies. And we're putting limits on them. But nobody's found a direct detection. There's been no direct detection. But if you're talking about this sort of seeing the effects of what we think is dark matter, that's getting better and better all the time. We are definitely convinced that something is going on out there, whether it's dark matter - or we're going to have to invent something else - that is still for the future to decide.
SHAPIRO: And by out there, you mean also in here.
FRANK: Yes, in here. We're talking about the fundamental structure of the universe, right? We think of the universe as being all of this stuff that we can touch. But what we're - you know, if dark matter and dark energy is true, actually, that's like the pond scum on top of this giant, dark ocean. Most of the universe, if this is true, is going to be in a dark form.
SHAPIRO: Is there a reason we should care about this?
FRANK: On your day-to-day life, probably, you know, not. But, you know, if all of us are concerned with our being - right? We all know that we're going to die someday. And we wonder, like, wow, what's the universe? What's going on? And, you know, this is an (laughter) essential answer about what's going on - that it could be that most of the universe is in this other invisible form. So it just raises the questions about how strange and beautiful the universe is.
SHAPIRO: That's University of Rochester professor and NPR science blogger Adam Frank. And if you have a question about physics, astronomy, science in general, send us a note. The show is on Twitter at @npratc. You can find us on Facebook, as well. Thanks, Adam.
FRANK: Thank you. That was great. Transcript provided by NPR, Copyright NPR.