The Supermassive Podcast - 59: BONUS - Why can't anything go faster than the speed of light?

Episode Date: December 13, 2024

From planetary alignment through the galaxy to spacetime expansion, The Supermassive Team answer your questions. Keep sending us your questions, email us on [e-mail] or find us on instagram @SupermassivePod

I understand that one method of detecting an exoplanet is to detect the dip in ma- uh? To detect the dip in magnitude when it transits a s- oh my goodness. I understand that one method of detecting an exoplanet is to detect the dip in magnitude when it transits its star. When it transits its star. God. Hello, and welcome to another bonus episode of the Supermassive podcast from the Royal

Astronomical Society with me, science journalist Izzy Clark, astrophysicist Dr. Becky Smethurst and the society's deputy director Dr. Robert Massey. Before we dive into the Supermassive mailbox, Liam in Amsterdam has sent in a brilliant email about our last bonus episode is, and I just had to read it because it's fantastic. It says, hello Astro podcasters, I love the nuclear pasta idea, you know, that we talked about on the previous episode.

Yes, strong agree. But Liam says, I think you've missed the solution on naming the field. Clearly someone who studies neutron stars is a pastrophysicist. Oh, I love it. How do we miss that? I honestly love this so much. And I really, I'm actually disappointed in us that we missed this because it's so brilliant. So well done, Liam. Yeah, well done, Liam. Yeah. He also says,

love the show, science education for the win. Which I absolutely yes. I think Liam gets a gold star for a very excellent email. Okay, so let's go to some questions. Robert, Sam has this question. They say, given space time has been expanding, wouldn't the volume of Earth or the sun, Milky Way, local group, etc. increase over time? If not, what does it say about the nature of space-time expansion? Yeah, that's a great question, Sam. Oh, and by the way, in passing, I definitely want a pastrophysicist on my office door. In my love of cooking, I've got to do it. Or run a column or something.

You absolutely do. It's got to be done. You do. Right. So anyway, Sam, it is a great question. So the answer is that the expansion and the dark energy we think is driving it, this weird stuff that we still don't know what it is again, happens on the larger scale. So we expect to see things like super clusters of galaxies, enormous structures, hundreds of millions of light years long, get to eventually disperse as a result.

But the smaller things, and certainly galaxies, planets and stars, there's much stronger local forces. Gravity on the smaller scale is much stronger than this expansionary force we think. So they're not expected to be pulled apart in the same way, you know, they're hold together. And on the very smaller scales, if you think about people and objects and so on, then they're held together by electromagnetic forces and they're very, very strong indeed, much stronger than gravity as well. So, you know, they're not affected by the expansion. There is this less accepted idea of a big rip, not, you know, pretty contentious where the expansion does eventually start to pull things

to bit. But even if that happens, it's going to be in hundreds of billions of years time. So, you know, not one to add to the list of dangerous things that can happen via astronomy. We can relax about that. Bekkah Okay, I'm Bekkah. Josh in Virginia asks, do you think that the recent finding that galaxies in the early universe are more massive than expected is potentially suggestive of how we get supermassive black holes that are too big to be explained by our current understanding of how they form and grow. Good question, Josh. So I think what you're referring to is like both JWST's discovery of galaxies

that are apparently too massive for our best models to explain. And then the supermassive black holes that have been found in the early universe by JWST that have masses bigger than we think should be possible for black holes to grow to in the time that they've had. Cause obviously light takes time to travel to us. So as we see more and more distant things,

we're seeing them earlier in the university's history. So for example, if we see like a million times the mass of some black hole, only like 500 million years into the university's history, you think how on earth has it grown that big in such a short space of time? Now it's an intriguing sort of question you've asked Josh about, like,

are they linked, those two things? Because in the local universe, like in galaxies that we see fairly nearby to, it was like relatively nearby, right? There is a correlation between the two things, like the mass of a black hole and the total mass in a galaxy. Like the two are correlated, right?

And we sort of interpret that as like the black hole grows together with the galaxy, right? They co-evolve, they co-grow. So it is definitely possible that like one could be fueling the other in the early universe. And that is something that people are looking into whether those like correlations hold or whether like the black hole grows first

or the galaxy grows first and then they move on to those sort of correlation lines that we see so in the local universe. Having said that, there's so many explanations floating around to explain either how the black holes got big or how the galaxies got overmassive. The thing that I think is most likely is that the galaxies that have been found are not actually that massive

as we think, right? The masses that we're estimating are estimates, right? They're also degenerate, right? So they can be confused with how distant they are in the models. And so that adds things to it. We also like don't know the spread of stars of different masses that form in the early universe.

We assume it's the same of the spread of stars that we see in the Milky Way. And we need to know that to say, okay, we've seen this much light here. So if there's this sort of spread of this different types of stars giving off the light that we think they give off, okay, that means that this galaxy has this much mass. But if you change that ever so slightly, then you're going to change the mass that you estimate and that you get out. And there's all sorts of different explanations from, it could be that dark matter doesn't dominate in the early universe to all sorts of different things

like primordial black holes might form in the early universe and that speeds up galaxies forming or black holes even forming. And so there's so many different things going around that I think it's just more likely that we don't know enough about the early universe yet to make any definitive conclusions. Like, yes, JWST has been what,

three years since launch now, two and a half years of science operations. That sounds like a long time, but in terms of getting science done and understanding things, we're still in the like swimming through confusion. Baby steps. Stage, you know, so it's gonna take time for us

to piece out, you know out all the puzzle pieces. We've got to turn them all over, figure out the edge pieces. We've got to then break in a group of my colleagues. It's going to take a very, very long time for us to figure this all out. I think we need to have a klaxon that is like, we just don't know button. Like when the QI alarm goes off. Yeah, I like that idea. Okay, Robert, Phil Banting has emailed us to say, further to the recent discussion

about space themed names for babies, on two mornings a week, I help run my church's toddler group. And one of our clients is a girl called Artemis. And we also had a girl called Luna. I hope that if either of these girls ever applies for astronaut training, she will get ushered straight to the front of the queue. But until then, our toy rocket will have to do.

That's lovely. Thanks for sharing that. Right. So now on to the questions. He says, I understand that one method of detecting an exoplanet is to detect the dip in magnitude when it transits its star. But that is only possible if the Earth is aligned with the orbital plane of the planet. This made me wonder whether planetary systems have even roughly similar alignment throughout the galaxy, or are they completely random? If they are random, there must be many exoplanets that are impossible to detect using this current technology. Thank you for your podcast, of which I am a supermassive fan. Wonderful. Thank you, Phil. Yeah, and a brilliant question, actually. I do hope Artemis and Luna

go on to do fantastic spacey things. Keep us updated. Or at least become an archer, one of the two. Exactly. But your deduction is actually pretty much spot on. So we only detect transiting exoplanets where the system is quite close to being edge onto the Earth. So in other words, that the orbit of the planet around the star is aligned in such a way that it will pass in front of it from our perspective. So if that isn't the case, then we won't see a transit if it's tilted, then you just imagine, you know, if you

let alone if you look at it face on you would the planet would effectively be going round around the star, but it won't block the light. And they're almost all of them are simply too close to their stars to be seen, you know, directly. So we just won't be able to detect them in the same way. However, and you know, it is also then fair to say we expect them to be entirely randomly distributed. There's no reason to believe that they would be preferentially lined up with the earth. You know, that'd be a very weird thing to be happening. So what we can then do is say well if we detect and we detect around 6,000 exoplanets confirmed already a huge number and bearing in mind we didn't know about any 30 odd years ago.

This is this is just a completely novel field still. Bearing in mind that number it implies there are a lot more out there that we can't detect directly, but we can just do some statistics and say okay then there'll be ten times as many as the number we can actually detect. And there are other ways you can find them. There's a technique where you can look at the way that the planet, if it's big enough, at least, or even if it's fairly small, actually pulls the star back and forth a bit and measure that tiny change in speed and velocity. I call that the wobble method. Again, the wobble method is absolutely fair. Make the planet wobble. And actually that still is better if it's edge on because, you know, if the planet is

going round again face onto us, then, you know, we don't see quite the same shift. So really it tells us that the universe is absolutely teeming with planets. We can assume that a huge number of stars have planets and that implies there really are a vast number of planets out there. Can I add something to that? Yeah, go for it. It's fun to think about how because transits are easier to detect because all you're doing is measuring the brightness, that's the thing we did first.

Which is why we know so many planets that are edge on. But the fun thing to think about is how many exoplanets that future or current surveys will detect with these different methods like Gaia. So ESA's Gaia mission, which is like surveying a billion stars in the Milky Way and it detects its motions. So you'll detect if there's a planet edge on that's making it wobble towards and away from us,

but it's also gonna do what's called astrometry, which is to get really precise positions of the stars. So if there's a planet completely face onto us, making the star sort of go around in a little circle, then we should also detect that, which we haven't been able to do before in a wide kind of scale. It's only been like individual stars that we happen to have been watching that you spot that, but now we've got this big survey. It's fun to think, you know, will we overtake the amount of planets that have been found because of the wobbles rather than because of the transits?

Like, I don't know, we could see like a shift in the field, you never know. Very cool. And Becky, we're gonna end on this zinger from Lizzie19 on Instagram who asks, why can't anything go faster than the speed of light? It's a zinger, we're really ending on a biggie there. Thanks Lizzie, you know, I was just winding down. No, no.

If you'll allow me, I think I did this question the most justice in a chapter of my book, A Brief History of Black Holes. If you'll allow me, I think I did this question the most justice in a chapter of my book, A Brief History of Black Holes. If you want to check that out Lizzie, maybe pop it on a Christmas list, wink, wink. But I will try and do my best very briefly on the podcast for you. So it's Einstein's theory of special relativity that tells us that like nothing can go faster than the speed of light. And it's all down to this idea of space-time. So not just space, but like the four dimensions, space and time, all intrinsically being linked together. And so in special relativity, as an object moves faster, so moves faster through

space in a given time, it actually gets heavier. So like, you know, when we think about how heavy something is, we're also talking about the curvature of space thanks to Einstein's theory of special relativity, right, in terms of how much gravity it has. And so if it's getting heavier, its mass increases. And therefore, if you remember Einstein's other equation he told us about, E equals mc squared, mass and energy are equivalent, then it's going to get a higher amount of energy and the amount of energy required to continue accelerating that thing that's getting ever heavier and ever more energetic, you know, if you want to accelerate at higher speeds, right, the amount of energy you need is going to increase. And so as you approach

the speed of light, the mass, or how heavy an object is, becomes so infinitely large that you need an infinitely large amount of energy to accelerate it to a higher speed and to the point that you just reach infinity. Right? And so if you actually plot this out, if you're a fan of a graph, right? If you plot this out, you get, who is a fan of a graph? Right? If you plot this out, you know, you get this sort of limits approach to the speed of light where you just keep, you know, drawing the line upwards and you never actually cross that sort of speed

on the X axis of the speed of light. So that means it is technically physically impossible according to Einstein's theory of special relativity, general relativity, to accelerate any object with a mass to exceed the speed of light, because it would require an infinite amount of energy that, you know, infinity notoriously difficult to reach. Is it just to keep skin bigger? It keeps going.

Amazing. Thanks for that, Becky. And that's all the time we've got for questions. So do keep sending them in along with your pictures, your baby name requests, your Christmas lists, anything else you need us to help with. We're here. We do love reading them all. So you can email podcast at ras.ac.uk or find us on Instagram. It's at supermassive pod. And we're going to be having a full on Q&A in January. So just pile them on send them in because we've got to make up all the episodes.

Yeah, exactly. We usually do that in January, don't we? It's a fun tradition that we've started. So yeah, we're really gonna need a lot of questions. Absolutely. Get thinking, get them sent in. Yes. And also we'll be back in a couple of weeks

with our end of year episode on the scientific search for extraterrestrial life, which is very exciting to think about all the ways that people are doing that. But until then everybody, happy stargazing.