Space Time explores the outer reaches of space, the craziness of astrophysics, the possibilities of sci-fi, and anything else you can think of beyond Planet Earth with our astrophysicist host: Matthew O’Dowd.
Episodes released every Wednesday afternoon!
Matt O'Dowd spends his time studying the universe, especially really far-away things like quasars, super-massive black holes, and evolving galaxies. He uses telescopes in space to do it. Matt completed his Ph.D. at NASA's Space Telescope Science Institute, followed by work at the University of Melbourne and Columbia University. He's now a professor at the City University of New York's Lehman College and an Associate at the American Museum of Natural History's Hayden Planetarium.
Previous host Gabe Perez-Giz is an astrophysicist who studies black hole physics. He received his Ph.D. from Columbia University and also hosted PBS Infinite Series.

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  1. Chris Griffith

    So, quantum loops are not actually loops, but math that defines space in ways that mathematically resemble loops? ...and those "loops" are more like definitions which are describing the actions(?) or vibrations of the states of the quantum foam, which is how space is organized?

  2. Chris Griffith

    The Great Filter Is: One "great filter" after another.

  3. Kurt Fitzner

    The one question I wanted answered was why the trapped modes don't add to a black hole's mass. Or, using the hack explanation, why when the event horizon splits mass/negative mass pairs does the black hole always seem to eat the negative mass half? Shouldn't that balance?

  4. Ghostcamel

    Hey Spacetime....... do you think 'Aliens' are just Elon Musk's grandchildren returning from a quick zip around the galaxy? Could you science how fast and far we would have to travel to go back to the 1950s? Could the Aliens, be Us? Maybe genetically modified to withstand the rigors of space travel?

  5. Robert Shackleferd

    What about all the hydrogen left behind?

  6. Al Garnier

    Expansion is the normal state of gravity free, negatively charged, electron scalar fields that collide along their perimeters to create spin (electromagnitism) and fusion of electrons into quarks & gluons. These collisions create a thermodynamic vortex of matter with a black hole at it's core, known as a galaxy. Gravity is the flow of electrons attracted by the quarks in protons and photons are the entropy of a gravity field.

  7. Rizaldi Ramdlani Pamungkas

    Heard about an experiment about some scientest simulate the creation of galaxy without dark matter, since u discuss bout dark matter and axion at the end of the video. Could it be true that dark matter is doesn't exist and doesn't necessary part to our universe?

  8. sadrevolution

    An astrophysicist denigrating linguistics dismissively as "important." Likely, this is because it is such an accessible field that has such immediate applications. I see your Sarcasm, PBS Space Time, and raise you one Irony.

  9. Patrick Kloes

    Quantum physics is the study of the very small. The meaning of an opinion is the in a way a principle of the very small. What I'm saying is that an opinion of another person is not relevant for "you" only if you want to collapse your opinion to someone else's opinion. Just a thought that i had a couple of days ago.

  10. Casey Jones

    I am a wave but identify as a particle. I am in the process of transitioning.

  11. Mystic Espresso

    If we were alone in the universe, we would feel it. Humanity, on it's own, cannot account for it's own evolution. There is definitely something else in place.

  12. James Black

    Watching you move I think your camera's exposure time is too small.

  13. Jop Mens

    I'm glad its gonna be about the quantum multiverse. It seems to me that the wavefunction is a superposition of different universe-reality-timelines that interfere with each other and that the collapse is only a loss of this interference as each timeline plays out differently, over time different probabilities may play out with regard to a "particle" and these differences may add up. So the apparent difference between the quantum world and the classical is about the same sort of statistical phenomena you get from throwing a die many times and plotting the results, giving you a different perspective on the same thing. Don't a lot of interpretations fail to account for this branching of reality and have problems imagining ourselves to not just exist on one isolated universe-reality-timeline?

  14. Millennium 7 * HistoryTech

    I hope not ... the universe is not ready

  15. AshyD

    Why would the universe being flat mean its infinite?

  16. John Paul Espulgar

    No they don't, they use the energy from the gravity

  17. Sebastian Keano

    and where is the Earth rotation in relation to orbital speed in that picture?

  18. Kwiji

    What if there is just something smaller than quantum particles? What if everything just swims in a liquid like state that create waves that we can't detect yet? What about gravitational waves, couldn't they just influence the quantum particles?

  19. djjfive

    All well and good for the scientific approach but try proving anything without consciousness...

  20. The science dude

    quantum mechanics says that a particle can be at two places at once. if we can say that a black hole's singularity is not something with no volume but something with infinitely small volume. there's a difference right? so we can say all the black holes in the universe are the same but forming in different points of space time. everything that goes into a black hole just falls through the hole and goes to place outside the universe which is not even a place but the object is all that there is over there. this means that information is also not destroyed. this could also be regarded as the black holes mass, entropy and hawking radiation could b from this.just a thought i had in school yesterday.

  21. Hero Syndicate

    The only reason they are confused is because they are reaching for answers in places there are none.

  22. Hero Syndicate

    Thats like saying the camera is controlling the actors. Or analyzing 3d with a 2d device. apples and oranges dude

  23. Max L.

    Just my morning thoughts... Since everything in the universe seems to be centred around energy - what if the quantum super state is more like a specific energy state... and since they loose some energy in the detection process, they loose the super state as well...? 🤔

  24. Franz Finav

    I’ve had mushroom trips less trippy than these videos. What a way to start the day!

  25. Matthew

    I fear that both camps, physicists and spiritualists, fail to truly understand each other. This video's quick dismissal of large numbers of works is evidence of that. I do agree, most spiritual authors, and myself, don't have a great grasp of quantum physics.

  26. Jagerbomber69er

    Happy day death 2U brought me here

  27. Yair Shahar

    We always have to re answer the same things because people lacking education recycle the same old stuff Not even really as questions 1. There must be a design. 2. There must be a reason 3. There is a purpose in the design 4. We are the "top of the chain" hence the above statements are valid. It is in the end the same experiment we can ask without going into quatum mechanics If a tree falls down somewhere in the universe and the conditions are right for it to make noise. Do i need to be there for the noise to happen? When the questions try and bring us back as the center of the universe because that is what religions falsely still states as absolut, Then we already know that the entire angle is wrong Lets move on

  28. Xakari

    Somehow more terrifying than anything I watched last year.

  29. Matthew Drodge

    This does not compute. I think my brain needs to be rebooted after that.

    1. Matthew Drodge

      I love watching these videos, I'm hoping to learn something one day the problem is I almost never understand what he's saying.

  30. Jos Bergervoet

    Matthew why did you have to present the *collapse* idea as a valid theory again? You could just have pointed out that no collapse is ever needed, when Wigner, his friend, his family, and any other obsever is always in a superposition (and all absolute facts and conclusions in their heads are also superpositions). Presumably you save this explanation for the next video? But anyhow, you now do what the popular press is doing: promote the mysticism of the old QM, with its collapse! (Sorry, but since Albert's not here I had to remind you..)

  31. Skrmng Hrd

    Didn't know Aquaman or the lil guy from game of thrones could be this smart!

  32. Craig Neilson

    so what would happen if the sun was to flip it's magnetic poles. Would that not have any effect on the earth? Since the earth is on cosmic journey through space, being dragged by the sun. Essentially, the earth revolves around the sun due to magnetic attraction between the celestial bodies. Also, if it has nothing to do with bit, then what would you say is stoping the earth from just going off on it's merry way away from the sun and fellow planets? This since we already suspect the sun is going through a magnetic pole reversal.

  33. D T

    A better name would be... Andromeda Milk. that is pretty much what it will look like

  34. Scoring digits, son.


  35. mattrgetz

    The amount of time it took me to view this video is greater that the sum of the seconds of each portion of the video that I watched

  36. RR JR


  37. RR JR


  38. RR JR

    If notE posstraction, definitive lee plawzAPPLE

    1. RR JR

  39. emixiak

    Imagine a single bee somewhere on the other side of the globe. The probability of extinction by a gamma-ray burst is less than you ever happen to swallow that bee.

  40. markleyg

    It is not just intelligence needed. They must also have the physical ability to manipulate tools and communicate complex ideas.

  41. Med Otaku

    Around 6:40 they're making a point that a neutrino must have mass because it can't travel at the speed of light. And thus experiences time. So photons have no experience of time. But what about when they slow down? Does this mean a photon might have some mass? Or that it can acquire mass after interacting with a field that causes it to lose velocity?

  42. The Georgia Web Warrior

    Did anyone else see a "Stargate" type ring with symbols abound them to move between or dial in on what there is at all the different pathways into and through to get to other Multiverses? Location in this video is 1:24 of 17:24.

  43. Ivan Korystin

    Can the observer problem be connected with a free will problem? They can somehow solve each other.

  44. Feint

    This video is a good argument AGAINST any of us ever pulling a lightsaber out of a snowbank that is just out of reach.

  45. Máté Herbay

    Is wavefunction collapse really needed to interpret quantum phisics? Maybe the wavefunction is the actual phisical reality and the clearly defined world what we see around us is just a perceived thing. Isn't there a way to formulate it that avoids the collapse totally? That would save us a lot of metaphisical debate.

  46. Jesus Da Lawd

    It sounds like we can just use the repulsion of multiple strong magnets to spin a really big magnet and create electricity

  47. Ayetar Poss

    👍 tne

  48. chase romnes

    By no you mean YES about manifestation. I can prove it.

  49. Daniel Kim

    7:58 Why was it weird that the wave equation of a Graviton was found when length was considered on another dimension? What if the length these strings are tightly related to gravity? They would be interacting at close to speed of light, and with the energy of the strong force why can't we have gravity appear by making it harder for them to talk to each other further away? Could it be reason why they are so tightly together in the first place? Must be a ridiculous amount of gravity required to rip apart a strong force.

  50. Mr r Allen

    but didn't we prove gravitational waves from big bang and the two black hole that created them right so we came from a black holes

  51. Avon Yeo

    I was thinking if we can create a technology where we can encapsulate a starship within a beam of light, then shoot this beam of light at the nearest star Alpha Centauri @ 4.367 light years from Earth, we can achieve a velocity of 100% light speed and reach it in 4.367 years. Of course we have to de-capsulate/decelerate the starship before reaching the destination at a safe distance. I call this the Particle Photon Encapsulation (PPE) Drive - a starship (particle) contained within a stream of Photons and riding it like data in optical fibre at the speed of light to the nearest star. This of course would be a one way trip because we need a powerful light cannon to lauch the ship to the destination. However, if we can make the starship generate it's own beam of light in the direction of travel and then encapsulate itself into that beam, then we can do away with a launch pad and the starship can travel freely. The starship is made out of particles (matter) and light is made out of photons (energy), so this kind of technology has to be able to encapsulate matter within energy - the reverse of the natural phenomena where energy is encapsulated (contained) within matter.

  52. Matthew Davies

    Most Western countries are at or well below population maintaining birth numbers now. It's only the, shall we say, less gifted who are still breeding but as they reach our level of for want of a better word civilization they too quit breeding. I think that's the real solution to the Fermi Paradox. Ultimately sex just isn't worth the effort.

  53. Rich Arnold

    This question was answered in the 60s: Mars Needs Women

  54. Joseph K

    Why can't you see the entire future of the universe as you approach the event horizon? Why is it only a small amount of view, and if it is what do we see in the rest of the view?

  55. David Bogard

    Consciousness has been proven to influence random number generators.

  56. Matthew Davies

    I know this is not a popular concept around NASA right now but seeing as we sure seem to be alone or nearly so perhaps we should start seeding water planets that we find with bacteria? I mean tailoring simple life to local conditions and delivering it with a probe. A very long distance probe. We could start doing the prelims for that project right now. I think we should.

  57. Sean Rodgers

    The snow melts before the end of winter even. Then it is not cold enough for snow again for 8 months at least. People grow crops at 60 deg. north. How is a slight cooling going to see snow last through the summer? 6 feet of snow melts in a few weeks with freezing nights and days at +3 to +10. That means that July and Aug will have to be cooler than mid March for snow to stay

  58. lasso atrain

    Is the universe finite? I think that because space is a vacume that it is a pretty good Indication it is a closed universe.

  59. Faybrian Hernandez

    No, we will not send people to Mars. Mars is outside of Earth's magnetosphere where nothing can survive the two way trip. Send a small animal, insect or even bacteria to mars and back before you send a human, they will not survive.

  60. W D

    No Jesus beard. No deal dude.

  61. Lemon Party

    Sick burn on Veritasium.

  62. Dustin Johnson

    I'm the only one that's real

  63. Roedy Green

    How do the shade petals work?

  64. eZwoodb1ne

    How to understand the chart at 2:47 ?

  65. GunLovingLiberal

    This video contains one of the best explanations for tides I have read. Thank you.

  66. Michael Buyna

    Why did you throw out the possibility of your friend being a conscious construct? That seems to be just as viable of an interpretation as anything else.

  67. Shane.thomas Miller

    Hmmmm not so sure this was the one that broke reality there was one though that changed everything as we all remember it but i forgot lol

  68. Genghis Galahad

    The one-eyed head friend wore a PAIR of glasses. Question is: How do the eye-heads taste coffee?

  69. shadowhawk

    how has this theory held up the last few years? Is Newtonian Physics not what we thought, or did this fall apart?

  70. Ben Miller This is a link to a joe rogan video from today about time before the big bang. Brian Greene mentions "Repulsive gravity" seeming in place for just dark matter. Can you provide a fact check? Most of Brian Greene's info seemed right, and he mentioned the north pole like you did, but still found his whole thing about repulsive gravity bizarre.

  71. Darth Decius

    In regards to information theory - does the photon carry with it any information that determines where it lands, how it's wave function is collapsed?

  72. Kid Sundance

    Cool but who the f*ck cares

  73. Das Boot

    Crap how the heck are we going to fix this.

  74. santhosh kumar Rai

    Idea rrr

  75. nairbvel

    It's obvious that my consciousness failed to create a specific reality because if it had, the video would not have totally changed to other subjects at 13:01. <sigh>

  76. Osprey Flyer

    Good Review 👍

  77. Punk Patriot

    Not to assume that I'm smarter than a Princeton professor of quantum mechanics, but the idea that our friend's brain is in quantum superposition, rather than a single electron on the detector array becomes stochastically available for excitement by a finite quanta of electron wave energy... it just seems unnecessarily solipsistic to go with the consciousness thing. Whatever the real answer is, it's probably not magic.

  78. Punk Patriot

    "Our physical world is made of objects not quantum probability clouds" Uhhh, beg to differ. Because I mean... isn't it though? It's just that the more massive a quantum object is (like say, an atom, or a buckeyball, or a strand of DNA, or a human body, or a planet), the smaller the wavelength, reducing the probability of positions to a more finite region of spacetime... right?

  79. taino1952

    By the time we have the technology to Terraform Mars, we'll have to use it on Earth.

  80. Jonathan Bega

    Has anyone attempted to run experiments around consciousness and wave-particle duality? For example, have a computer record the results of a photon detector (left or right), but destroy the data in an irretrievable way so that a human observer (conscious entity) could never tell which slit the particle went through? If wave patterns still form, perhaps consciousness is more important than we posit. If no wave patterns, then we know that detection without consciousness causes the collapse. Etc. etc.

  81. Brandon Mcrorie

    the "ideer"

  82. Agustin Etchevers Reyes

    But second law of thermodynamics is true for closed systems (you can decrease entropy in open systems like fridges for example). So what if the universe is not a closed system? White holes are possible then?

  83. bob mar

    How do you keep from dying from radiation?

  84. Brian Lochrico


  85. AnubisAlex

    I think the Maxwell's Demon could be the answe to Electrons and Positrons not being Equal in the universe

  86. Ranyere Deyler

    This guy ( "proved" in this video that bells inequality wasn't actually violated and that the problem is only on the inefficiency of the experiment in detecting the photons. What would mean that hidden variable is possible. Can you disprove him? I confess, even being a physicist, that I can't. I may be missing something, as might him. It would be interesting if you comment on it.

  87. Blow Me

    Hi Matt, your video is actually wrong because Conor Mcgregor proved you can bring your dreams into reality if you focus hard enough

  88. MabDarogan2

    Reciting pi never fails to open legs.

  89. MirceaKitsune

    On last thing: At the end of the video where you explained both the observer and their friend observing the result at the same time, a very hasty conclusion was made. Only two choices were listed: Either you and the friend experience the same result, either you must conclude your friend is made up by your imagination. There's actually a third possibility... and it will make people's heads spin, I know it did mine: Both you and your friend experience different conscious realities, which includes different versions of one another. This is a very bizarre thought but one I've gotten used to: That when you talk to another person, you may perceive a newly branched version of them each time, while their consciousness may be perceiving a different version of you doing something else at that moment.

    1. MirceaKitsune

      I don't presently have the time to go in depth into my theories and thought experiments as to why this is true... especially since few people are likely to read those comments, and most who do will just try to ignore the question convinced of a given mindset. I'll offer this one though: We have two people and a rocket that can travel close to the speed of light. Person A stays behind, person B boards the ship as it takes them around the Earth at 99% the speed of light for a few minutes. Once the ship lands back and person B gets out, person A will be older by a certain amount. And yet, both person A and B experienced time passing at the same rate, relative to their own bodies and surroundings. This implies a consciousness offset: Neither of them could be perceiving the exact same present, one conscious mind remains in the past the other is perceiving the future. Yet person A and B can still meet up and talk to one another! Creepy isn't it?

  90. MirceaKitsune

    It's sad to see even an objective science channel struggling not to reject a very valid theory due to materialistic culture. The video didn't even mention Dean Radin, who has repeatedly confirmed that meditators are capable of influencing a double-slit device from a distance and even posted graphs showing consciousness influencing the probability... all because materialist scientists pretended to try the experiment without training their minds or even keeping them open, get no results, then go like "it won't work for us and surely it's not our fault so it must be fake because mysticism lol". I for one have no doubt that yes, consciousness collapses the wave function. Or rather sub-consciousness... obviously there's a reason why we can't influence reality directly with our minds, or rather only can on very tiny scales with an extreme amount of effort. I've done a lot of thinking on this in the past, and there are inexplicable paradoxes to the absurd idea that consciousness is just atoms generated by the brain. If anyone's interested I might dive into those arguments, although last time I tried to the response was along the lines of "you must be wrong and there has to be some materialistic explanation even if none of us can find it".

  91. Jasper Stephen's

    Strange that every time dark matter is looked for its not there. It would be really nice to actually have proof of the mythical dark matter

  92. Jeremiah Chavez

    I want to watch these videos so bad but I can't stand watching this guy narrate the video

  93. Jake Costanza

    It's interesting to note that humans think of the alleged simulation as something that obeys the same rules and principle our universe does.

  94. Михайло Заклецький


  95. NegativeBurn

    you are a gross shill

  96. Edison DiBlasi

    As a classics major, I would have to go with a hard c in Principia. As for the chimps and monkeys, I'm less concerned about that than about why our ancestors weren't either australosimia or notopithecines...

  97. Jwb52z

    If a consciousness observing something does not actually create reality, then they should not have used the word "observer" in so many parts of the science. Other than the idea that the observation and the collapse are not dependent on the conscious observer, you could also theorize that human consciousness itself is just what is required for the wave function to collapse, but that doesn't mean that the observer personally makes it happen on purpose.

  98. Jordan Bailey

    What about the past hundred years the world has gotten smaller how will that effect things how would we know its never been this small before and only getting smaller

  99. Eric Poot

    It's on watching all of this that I want to go back to believing pilot wave theory explains it all... I'll have to watch those vids again to remind myself why not. I hope I'm convinced - mysticism is so inconvenient for my state of mind!

  100. HeyokArmorR Tygersharkk

    From a physiological point of view wouldn't this imply there is no collapse and it is merely a delusion of a limited mind & sensory receptors?