An Astrophysicist's Top 10 Unsolved Mysteries

it's my birthday this week so to celebrate I thought I would compile a list of my top ten unanswered questions so these are a mix of questions I get asked all the time by people who are curious about space probably like yourself watching this video or that I think are the most interesting unanswered questions and remember the fact that we don't know the answer to these questions is a good thing because it means there's more to learn more to know and more progress to be made you might not agree with this list they'll let me know in the comments below if you think there is another unanswered question that I have missed this is my top 10 though I mean they're not actually ranked in order even though the numbered 1 to 10 I couldn't possibly rank them at all I thought show favoritism to objects in space although anybody that actually knows me at all will know that if I was really hard-pressed the black hole questions would win out in the end which is why we're starting with number 1 what's inside a black hole first up if you're picturing a black hole is literally a hole in space that stuff falls into and is lost forever stop it's not a hole a black hole is a place in space that has so much stuff in it that it's the heaviest thing in the universe black holes grow by eating or what we call accreting more matter so really I guess we should be calling them Black Mountains because they're essentially these huge piles of matter in the universe that we can't see because we'll never get any information from them because their gravity is so strong that light can't escape the question is though obviously what happens to the matter that crosses the event horizon of a black hole that adds to that mountains mass unsurprisingly we don't really know the best clue we have is sort of from the Pikachu to a black holes right you write this sort of pre evolution side of things is a neutron star a neutron star is the after the core of a star that's crushed down so much though all you're left with is neutrons that are as tightly packed together as they possibly can be the thing is though if you keep adding more and more mass to that you eventually the gravity is so strong that it overcomes the forces stopping the neutrons being squashed together and then that's when you have a black hole but of course because we can't observe what that matter looks like because we can't get light from it we have no idea what form it takes once it gets squished maybe it is a whole new form of matter that we don't know about maybe it turns back into pure energy because e equals MC squared as Einstein said but then again maybe we'll just never know next up what is the universe expanding into we don't know it's a bit of a misnomer that question because technically it's not a logical question to ask so yes the Big Bang created everything in the universe that we see around us but it also created time and space itself they didn't exist before the Big Bang if space only exists in the universe then asking what the universe is expanding into doesn't make sense because you're asking for a location and a location can only be found in space which doesn't exist outside the universe now having said that there are a lot of hypotheses floating around the theoretical astrophysics community that there are multiverses ie our universe is not alone there is not just one single universe there are many universes and ours is just one of many and so that as ours expands the universe is that we are somehow connected to around us they contract because we're expanding into them perhaps that's purely theoretical though and it probably always will be but never say never you know physicists might think of some clever way of saying if these exist it would mean this in our own universe and we can test for that but this idea of an expanding universe leads us to our next question what is dark energy or to put it another way what is causing the expansion of the universe what we do know though is that the universe is definitely expanding when we look out into space on average all galaxies are moving away from us and that really was the smoking gun evidence for the theory of the Big Bang but it doesn't explain why that expansion is happening there must be some force or energy that's pushing the universe out that's causing space to expand now we call that energy dark energy but just because it has a name doesn't necessarily mean we know what it is we don't even know any of its properties either all we know is that it's exerting this negative pressure ie a pressure pushing outwards counteracting gravity and it's currently winning that fight speaking of dark things next up is what is dark matter made of we don't know now unlike dark energy we actually know a lot more about dark matter and its properties I made a video a couple of months ago on the history of how scientists but grudgingly came to the conclusion after you know decades worth of research the 85% of all the matter in the universe was actually this dark matter dark matter is essentially matter that doesn't interact with light so it doesn't absorb light it doesn't emit light or it doesn't reflect light either so that means we can't see it but just because we can't see it doesn't mean we don't know it's there you ever seen a million dollars no think about the wind right you can't see the wind but you see the trees move and so you know it's there so we have a lot of similar evidence but in space of dark matter existing because it interacts by a gravity and that's how we know that it's there and from those observations we've been able to a couple of its properties the thing is those properties don't line up with any of the types of particles that particle physicists know about so it's obviously some type of matter that we have never thought up before if we could detect them here on earth then we might have half a chance but until then we're gonna be as ignorant as humanity was say two three hundred years ago when we didn't know about atoms we knew that we existed but we didn't know what we were made of sticking on the matter theme the next question is where is all the antimatter no wonder I did a recent video on this but I still wanted to include it in here because I think it's such an important question now unlike dark matter which is incredibly abundant in the universe you know 85% of all the matter in the universe antimatter is incredibly rare and that's the big question why is it so rare so antimatter is essentially the opposite of normal matter so if you took an electron which if you remember high school physics is the particle that goes round the centers of atoms electron has a negative charge if you had an anti electron which is called a positron it would have a positive charge it would be it anti particle and if the two of those things met they would cancel each other out and they were turned back into pure energy e equals mc-squared energy and mass are the same thing according to Einstein and we call that process annihilation now all of our scientific theories predict that in the Big Bang there should have been equal amounts of matter and equal amounts of antimatter made there was no preference to make one or the other if that's the case though then everything should have just denial a didn't turn back into pure energy again but obviously that didn't happen because we're now surrounded by universe made of matter antimatter is still made in natural processes like radioactive decay in fact bananas are a massive source of these anti electrons the thing is they just don't hang around for very long before they end up meeting a normal electron and turning back into pure energy again so people are still trying to figure out in these huge big particle physics experiments like there isn't CERN why more matter than antimatter was created in the Big Bang sticking on the Big Bang theme the next question is what happened in the first naught point naught naught naught naught 1 seconds of the universe or to put it another way 1 times 10 to the minus 43 seconds because I don't want to say 42 zeroes all over again not only do we not know we don't even have the maths to know this one because at that point the temperature and pressures in the universe are so high that the four sort of fundamental forces of physics so gravity electromagnetism the strong and the weak force that look after sort of binding atoms together in radioactivity they all merge to just become one like mega force and then nothing behaves like it should do anymore in fact if you use Einstein's theory of general relativity which best theory is you know it describes nearly everything we see in the universe in terms of gravity anyway and you try and use that theory to predict what is happening at that time you end up with what's called a singularity so people might have heard of that term in reference to black holes where you have an infinite amount of matter in an infinitely small space same is true here but it could be an infinite pressure an infinite temperature and in for an amount of matter in an infinitely small space what ends up happening is you have to divide by zero and we know that mathematicians do not like dividing by zero but even general relativity is probably thought to break down at that time especially if the four forces merged into that one big mega force because then it wouldn't describe everything properly but also because there's probably loads of quantum effects that dominate on really tiny scales which it probably can't describe properly now you're probably okay with not knowing what happened in the first one times 10 to the minus 43 seconds if the University of probably not losing any sleep over it but you can bet the theoretical astrophysicists well they definitely are moving on from the Big Bang by a couple of hundred million years or so up next is what came first the galaxy or the black hole we don't know so after the universe has been around for a couple hundred million years or so and you know everything's had time to just chill out particles of had chance to form atoms have had chance to form everything started clumping together under gravity no dark matter in normal matter and stars might begin to form the question is what came first though then did a collection of stars form ie a galaxy did one of them go supernova it become a black hole and then start to take in more matter and grow and grow until it became the heaviest thing in that collection of stars so it sunk to the center and over time grew into the supermassive black hole that we know exists at the center of every galaxy I actually did a video on how we know that about a year ago was actually one of my favorite videos I've ever made so go try that out if you're interested or the other option is instead of gas clouds in the early universe collapsing to form stars first what if those gas clouds directly collapsed into quite a large black hole in the first place and then stars started to form around it in a galaxy so the black hole was always in the center from the very beginning it's kind of like the astrophysics equivalent of the chicken or the egg I guess then there's actually been hints that direct collapse into a black hole of say 10,000 times the mass of the Sun in the very early universe could actually be happening is in we actually have observational evidence of that happening from the Hubble Space Telescope which has got a lot of people really excited and whilst that single observation is very promising you can bet we're going to need more than one thing to turn that hypothesis into fully accepted scientific theory and now something completely different what causes fast radio bursts if you haven't heard of fast radio bursts yeah well get ready because your minds about to be blown they are incredibly short like millisecond bursts of radio waves coming from space we've been able to pinpoint their locations they're coming from all across the sky from all different areas and we know just shy of a hundred or so of these fast radio bursts and we still don't have an explanation for them they're kind of this generations pulsars right pulsars were these very regular bursts of radio waves that we're coming from space that we eventually figured out where neutron stars that were rotating and they had this sort of beam of radio waves coming out of the poles and they were acting a little bit like lighthouses when they first discovered pulsars they nicknamed them LG my little green men because they thought they were aliens and obviously once again fast radio bursts everyone's like the little green matter back but I hate to disappoint guys but it's never a lien but unlike pulsars these things are not regular some of them we just got one burst from them and never heard from them again some of them we have seen them repeat except they've repeated with no pattern whatsoever so the number of hypotheses just floating around it's just there's hundreds of them everything from supernovae to gamma-ray bursts to black holes two neutron stars to magnet arts to Blitzers there's so many weird exotic things that people are coming up with to try and get an explanation for what we're seeing it's likely that it probably is something to do with these magnetized or blitzer something where you've got a very high magnetic field that's maybe producing these radio waves but the long-running joke in astrophysics is that we don't understand magnetic fields which is probably why this question is still unanswered which brings me nicely to my next question why does the sun's magnetic field flip every 11 years we don't know so the Sun actually goes through an 11-year cycle where I'll have a period of peak activity where I'll have loads of sunspots and it'll burp off a load of high-energy particles that gives us really spectacular Aurora on here on earth and then it'll go through a period of a lot quieter activity on this 11-year cycle and combined with that the magnetic field every 11 years sort of dies off and shrinks down and then it goes down to sort of nothing and then it bounces back again but with the North Pole switch to the South Pole and the South Pole switch to the North Pole and this is nothing to worry about it last happened in 2013 I'm sure you'd never even noticed it happening it also happens here on earth though as well but nowhere near as regularly it's only happened on earth something like 80 times in the past 183 million years that we know of at least and we think we know what's causing that as well because the earth has a liquid iron core and moving liquid metal sets up a magnetic field and so if you disturb that movement somehow either with an impact or because of like tectonic plates and volcanoes and earthquakes and whatever then you might disrupt that movement and therefore start this sort of shift of the magnetic field but on the Sun you've got this regular periodic flipping every 11 years that we just can't explain normally because we don't have a very good model of what's going on inside the Sun it's one of the reasons that people are still studying the Sun in so much detail because even though it's our star at a local neighborhood of space we know very little about it relatively anyway we know a lot more about it than we do other stars but it's one of the reasons why say ESA's solar orbiter has just been launched and NASA's Parker Solar Probe as well they're some of the missions that are trying to find out more and more about the Sun so that we can answer this question and many more just like it and finally the question that humans have been asking for millennia does life exist on other planets are we truly alone in our universe honestly personally I don't think we'll ever know having said that statistically I do think it is likely that life exists out there somewhere you know we are one planet around one star of hundreds of billions of stars in our galaxy the Milky Way there is an uncountable number of galaxies out there trillions quadrillions of galaxies all containing hundreds of billions of stars I think it would be incredibly incredibly arrogant of us to assume that we are the only one planet that managed to have the right conditions for life the problem is how we'd ever confirm that life existed on a planet elsewhere like think about it imagine if we found a planet that was almost identical to earth you know the same mass same size same length of year and it was orbiting a star that was almost identical to the Sun and we found the same signatures in its atmosphere as we have in our own atmosphere what then would that be enough to conclude that life existed on that planet I don't think it would be I think you definitely found the candidate for the most earth-like planet elsewhere in our galaxy but I don't think you could say for definite whether life existed on it or not and you might just say okay Becky well let's just go to that planet and find out but what if that planet is say tens hundreds or even thousands of light-years away what then but you might think that's fine we'll just kick back and wait for them to come to us hopefully peacefully but they're gonna be limited by the same laws of physics we are they still can't go faster than the speed of light just like us so if they're coming from the other side of the galaxy then you know we better hope they left when the dinosaurs were still alive so despite being the biggest question of them all and one that yeah I would love to definitively answer it's one I think we just all will have to accept that we might never know the answer to that yeah editing Becky here just before we get to the bloopers I want to take a minute this week's sponsor brilliant brilliant is a problem-solving website that gets you to learn by doing not just by watching youtube videos so one of the things I always get asked or told is that someone wants to be an astrophysicist but maybe 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Becky that's dr bees DK why and sign up for free plus the first 200 people that go to that address will also get 20% off an annual premium subscription - it is sponsorships like this from brilliant that allow me to keep chatting science with all of you guys and for you lot to take your interest in science further so head over there and give them a big thank you for me change in the battery it's Sunsail to the stem that's like a parody of a parody some weird one Becky anywho where was I oh yeah don't matter so one of the things I always get asked emails dm's whatever it might be oh my arm you

Channel: Dr. Becky

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Keywords: space, astronomy, astrophysics, solar system, the sun, aurora, northern lights, planets, physics, science, dr becky, dr becky smethurst, rebecca smethurst, magnetic field, plasma, hubble space telescope, hubble, nasa, esa, dark matter, cosmology, dark energy, unsolved mystery, unknown, black holes, aliens, exoplanets, fast radio bursts, big bang, antimatter, expanding, universe, galaxies, extraterrestrial life, top 10, sun, earth, einstein, general relativity, grand unified theory

Id: 8ehoj-y3b1s

Length: 21min 59sec (1319 seconds)

Published: Wed May 13 2020