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. Kallian Publico

    What is not stated definitively is why a single particle would recognize any size slit as an empty space as opposed to a "wall". Much less a "photon" which has less mass than an electron. How many particles bounce back off the wall? I'm not convinced of the design of this experiment. Wouldn't the wall have to be made of pure "neutronium", a densely packed element whose substance came from a neutron star. A single particle couldn't get past that it would definitely bounce backward. Also the wave theory of light is based on a structure halfway submerged in a pool; that means there's water on both sides already. If there was water on one side of the structure and you opened up 2 slits the water would fall to the ground like it was leaking. Now if you did the experiment in space and shoved water thru 2 slits with no water on the other side that would be something.

  2. Jack Doyle

    Without the Copenhagen interpretation isn't there no free will?

  3. MarsJenkar

    If you're watching from one of the playlists (which for some reason don't have the answer to this particular challenge question), the answers are given here:

  4. Ali Maghsudi

    After a few months of watching, I finally catch up on the latest video. Quite a journey. The only problem now is I have to wait one week for a new video. Thank you for all these great videos.

  5. ajr993

    What would happen if you used a theoretical super precise mass energy sensor next to the slits? So instead of interfering with the pattern, you are just observing the effect on space time as the photon passes through the slit. If you did this you would not cause decoherence. Would you detect a space time disturbance in both slits? Would the space time disturbance only be half as much as you'd expect since the photon is divided between both?

  6. Jeremy Pickett

    While I understand your words. And I get your math. It is still insane. Space is weirder than any sci fi novel.

  7. Shawn Elliott

    Okay, so if I understand correctly, the smooth predictable behavior of classical physics is the result of multiple quantum timelines getting blurred together and becoming indistinguishable? When we observe quantum effects we are observing individual distinct timelines, which is something we're not used to seeing because our everyday lives consist of quantum countless timelines blurred together, which is why quantum effects look so weird to us?

  8. Carsmc1

    watching this after taking some edibles is quite a trip

  9. Philipp Schmidt

    @PBS Space Time Hi Matt, could you link to the Paper you mentioned at the und?

  10. AL Can

    You're missing something HUGE. Everything used in the experiments have one important thing in common. They're connected via their power source. I'll let you figure out the consequence...

  11. foxpup

    More experimental results please and less theorizing. The truth is in the emperical data and only with that can we generalize and do real science. Do A in context B and get C Expand the scope of what gives you the same results and generalize as much as the data allows. Do the same with different actions in different contexts and classify and group the results. Build imaginary (mathematical or otherwise) models that explain results when possible. That's doing real science.

  12. Ricardo González

    Great video!

  13. FeedEgg

    (Energy = Entropy) Everything else is in the middle for some reason, it is.

  14. Damian Vigorito

    Well if your padre pio and can bi locate and be in 2 places at once. But hes catholic and thsts jesus

  15. FeedEgg

    omg they're like chromosomes! of course! I always knew we would understand the entire universe one day, it is almost here.

  16. FeedEgg

    Black hole divided by zero, BOOM!

  17. FeedEgg

    Yea that's the thing with huge theories that involve QUANTUM physics....think about it for a second. QUANTUM PHYSICS. Can only observe when still...when moving it is wrong when still it is right....oh no my brain!

  18. teflontelefon

    u wot m8?

  19. Chris Vlahakis

    Okay all you physicists and scientists, since you claim you're smarter than this mouthpiece, try to make your own ALsel videos and tell us what you think about what happened before the big bang, I'm all ears....

  20. Chris Vlahakis

    Has any physicist calculated the possible speed of inflation, since the expansion of the universe is faster than the speed of light, there must be some exotic matter, aka dark energy behind the scenes running the show. Could tacions be the possible culprit in the cocktail of particles that fuels this expansion?

  21. Michael B

    I'm not a scientist, neither am I a great writer and I dont think I'm right about everything of course, but intuitively, I believe that the speed of light has EVERYTHING to do with all things in this known universe, at least for now because light is what we use to measure the space time continuum that WE exist in. Light speed may differ in different universes due to the density of that universe. Light speed is what can be measured. The speed of light simply is the amount of time it takes light and EVERYTHING associated with it to travel. Period end of story. All this stuff about causal this and causal that is a bunch of BS in my opinion and probably Einstein's opinion as well. Why we complicate everything is beyond me. This universe is built upon an algorithm that was designed and created by demigods that had and still have the free will to utilize and convert original source energy into what we now see, feel and observe as dense matter and there are numerous, if not infinite degrees of density which is energy that vibrates at whatever frequency it is programmed to vibrate at. Those differences in vibrational frequency is what allows other dimensions to exist as well and not just this one. Light is energy which exposes itself in and at varying degrees of vibration depending on the density of the particular dimensional density that light is in. It's all relative. The chair you sit in this dimension is light and so is your body as well as the water you drink, but each of those things vibrate at different frequencies. That's what makes them different, yet they are all light, just different densities of light. Everything in the known universe is made up of light, which also includes the dark energy that scientist are still trying to understand. What you see as light in this universe may or may not be detected in other dimensions because of the differences in vibrational rate. God allowed light to be created by those parts of itself that became self aware and as a consequence inherited the gift of FREE WILL to do what it wanted over eons of time. That's why we are all screwed up. We created the tree of knowledge in a sense and learned experimented with algorithms, forgot who we were and became the demigods that you read about in mythological literature. Those demigods created this universe and probably many others. Thats probably why Aliens exist. God does NOT need to create universes, only demi gods who had no idea what exactly they were getting themselves into with all their new found power which leading to greed and corruption, just like we have today. We are the children of the demi gods who created the algorithms. But all that was created by those whose separation from SOURCE, created, and were and are all related to SOURCE. Now all of these entities who originated from SOURCE are beginning to realize that the only way to true peace and harmony is to RETURN and be one with SOURCE but this time maintaining there self awareness outside if the VOID of GOD the source of everything. Unfortunately, there is much karma to overcome due to the separation of those parts of Gid which became self aware and misused their power. We will get back to source eventually but it will take time for our energies to reach the purity of energy that is GOD in its purest form and because SOURCE is infinite, there will probably always be this cycle of beings that separate and eventually learn that the their purpose as is all of our purpose, is to go back and be one with source. There in its purest form where THERE IS NO VIBRATION. It is the VOID which is GOD. Its all about something from nothing while at the same time that nothing is indeed EVERYTHING! I guess that's what they call the greatest OXYMORON that ever was and will be. But somehow it all makes perfect sense.

  22. Mike Ramirez

    Sounds like fun. When do we leave?



  24. MeeK1447

    My theory in Dark Matter Is that dark matter is a Particle that we know of, just at a different State of Matter that we are unaware of. (Part of my MeeK Electron Theory) P.s. Particles have mass and energy Electrons are have a Negative Charge

  25. Alex Podolinsky

    Can you guys cover quantum Darwinism?



  27. Mario Solorzano

    dam it really do be like that

  28. MeeK1447

    The Big Bang is actually Constantly Occurring Think about it, the universe is expanding like a real explosion So this CMB could be showing "Dark Matter" as it existed longing than we know it does. Oh snap! I made this comment at the start I think I have the most understanding on Dark Matter

  29. MeeK1447

    Hey I Believe I solved Dark Energy and Matter I have created a Scientific Theory of my own that makes sense with the laws of Physics. Dark Matter and energy is real, just misunderstood. Ps. In my theory Dark Energy does disappear. I could explain how but I want to prove this theory by having scientists debunking my theory.

    1. MeeK1447

      I need real scientists to debunk my theory I also have a way to prove my theory just need help from scientists.

  30. Omar Delawar

    Hey PBS team! I just wanted to give you guys props for using the metric system in your videos! Leading by example! I really hope more organizations and ALselrs, in general, adopted the metric system so we can join the rest of the world and make the US all-metric! It's a better system, period.

  31. Orion S

    If the universe is a simulation, the parallel worlds whilst you don't know the result are hanging in RAM. Literally, if you perform 100s of these at the same time for the same person and have trillions of alternate states of reality, you might die just not knowing the result :P RAM output will be so high god will just kill you like we force quit an app :p

  32. Lit E

    Trying to isolate a slice of the global wave function in order to maintain its coherence kinda brings back the issue of man trying to be an objective observer in his reality outside of himself, it also gives the radical idea that understanding the entire global wave function and being able to do experiments on it would probably mean that there is no objective reality

  33. Raintree Refuge

    "It's only 4.4 light years again"

  34. Ross Galloway

    This is an incredible, mind-blowing episode that really expands on so much about why the double slit experiment is what it is, cleans up the Measurement Problem and adds so much richness to the Many Worlds Theory! I'm Sold.

  35. Caterpillar

    The intro music always makes me jump up and twerk like a little ho

  36. Evil Betty

    could gravity be influencing the particles in some way causing them to behave like waves?

  37. Brad Villiere

    Totally called it! You can't measure the light without distorting it. 9 min in, thank you, I always had a problem with this part of the experiment. The detectors and measuring devices are deceiving. There are no particles, only waves?

  38. mmartinisgreat


  39. MeeK1447

    Hey I got a theory on "Dark Matter" that I believe you'll enjoy Debunking. Just reply and we'll figure something out to discuss my theory.

  40. CriticalCK

    Is it true that the carcadian rythm mimics the duration of a mara day instead of 24 hours?

  41. iceman-ny

    Nice to see all the SOs in here refuting this fantasy video. Truth escapes them. Sadly this is PBS wasting our tax dollars.

  42. Faybrian Hernandez

    Lets do another calculation for the probability of getting bacteria on Mars to process dirt. I am just joking because even the most insane extremophiles wouldnt live more than a minute trying. Forget it guys, Mars is out. Earth is all we got, love it or leave it.

  43. Pablo Gutierrez

    Wwwwwwoooooowwwwee !!!!!

  44. Gruff Tor

    The force is weak with this one...

  45. Matthew Bernobich

    this guy projecting humanity into the next millions of years as if we won't die from climate catastrophe by 2100 (if i'm being generous)

  46. Tripcore

    'Random phase offset' False. No such thing as random.

  47. Johnny Carrion

    Cartoon please cut the crap

  48. Monster Hunter For Smash

    U n b r u h*

  49. StaRMaestroS

    Many worlds just feels so lazy. Like creating a fantasy movie and then claiming it was all a dream to tie up your plot holes.

  50. Nat Clo

    Global consciousness collapsing wave functions Yes please, this is the hill i will die on No free will, cant be helped

  51. Alexander Johnson

    Damn that one was good...

  52. Frank Shifreen

    Hate the music- very disconcerting

  53. Howard Miller

    What I wonder is, what does that monkey see just before it reaches the event horizon? It seems to me it should see the entire universe age trillions of years and go completely dark.

  54. Jason Himsonson

    I like the way he says, "Paw-ticles."

  55. Globule Agrumes

    Very interesting topic and it's very well explained. Even if a lot of people already guessed that there's large fortunes to be made with asteroid mining, few of them are aware of the fact that the race has already begun! Also, I like the prediction Neil deGrasse Tyson made about the first trillionnaire being a space miner; if he'd be wrong about it, there wouldn't be legitimate businesses committing serious amounts of money in such projects: if they do so, it means they're confident enough to invest the funds knowing that they're going to generate a profit anytime soon, or at least during their lifetime. I didn't know the Grand-duchy of Luxemburg is a leader in that field, but it makes sense to me: there isn't much natural resources to be had in that very small European country (Earth is mostly depleted anyway, unless one's willing to pollute a lot to extract resources) and Luxemburg is also a country where banking and other financial institutions made a lot of money available. Otherwise, the ones that are still investing in oil, gas and coal will soon find themselves in a tough spot: with a global trend towards green energy and large movements protecting the miner's rights, extraction and refining is going to cost more, until those industries become unprofitable... I hope the only place where people will still be allowed to pollute is in deep space where there isn't any permanent residents yet... but then space will be humanity's next garbage and the pollution will be difficult to manage!

  56. Dercio Silveira

    So, it appears that eveything happens on horizon...

  57. Victor Landry

    And you do Paul?

  58. John titor

    Dubble split has been thought to behave simulative. And if that partical action was the case I would think would explain just about everything.

  59. GoldenTreesYT Minecrafter

    There are now infinite realities containing a guy who talks about infinite realities

  60. Nope Nope

    Hey I’m from the year 2020, Australia is just ambers and everyone is dying cause some corona

  61. Nope Nope

    This comment section is why we won’t ever get past mars

  62. enoughmonster

    Space is so magical. I cant get enough. I have videos in a playlist on repeat. Even watch it sometimes and listen to music I like imagine me travel the space fast feel driving the racing car with rokk music deltaparole tool foofighters nirvana and other.

  63. Daniel Prieto

    @pbsspacetime a question I had for a while is when two black merge into one for instant and "form" a gravitional wave, is there just one single riple at the moment of merge, or are there many riples. Also would this newly larger mass black hole form continues riples as it traverses space-time or not( that is to say to an object that created a gravitional wave created a path of gravitional waves as it moves)

  64. John titor

    So one of the two observers is wrong dispite evidence? Measure the photons with multiple teloscopes and live stream it

  65. PlebzOr Blapparapp

    I saw a double slit experiment on the internet once, when I had a lot of tabs open.

  66. Jeremy Byington

    At 9:52 what is in the mug? Visine?

  67. Jumpin Jesus

    The electrons in the wire are traveling much slower than the information in the electromagnetic field but because there are so many of them they add up fast it's hard to imagine one electron even being detectable with accuracy. Weird stuff.

  68. Louis-gabriel Calix

    and what does decoherence do in terms of information? Does it increase entropy by fixing a wavefunction of infinitely many states into a specific random state?

  69. Corby Ziesman

    Considering the vast amounts of space and time between even solar systems, I wouldnt be surprised if every quantum experiment ever performed on our planet so far is just a "don't care" in terms of the overall universe. Maybe we are just a bubble of decoherence which closes back up once we all settle down. And all the multiple timelines that happened on Earth become indistinguishable from the rest of the universe's perspective because they all lead to the same final state and it didnt affect anything too far reaching at all. Unless some radio waves or Voyager is the first domino in some long chain of events.

  70. Zes


  71. UpAndOut

    If you're measuring the quantum wave function, then you've become part of the quantum wave function.

  72. dwheel39

    How does a purely conceptual model cause anything? There is no such thing in reality as "spacetime " obviously (it exists soley in Einsteins imagination and his maths) but we are told that the bending of space (categorical fallacy in itself ) in the 4th dimension produces an effect (gravity) that causes planets to orbit , apples to fall to the ground and oceans amd atmosphere to stick to a spinning rock that blazies through a sky vacuum at 66,000 mph. How??? No wonder that Nikola Tesla (an actual practioner of science) referred to Einstein's work as a beggar clothed in mathematical garb that dazzles dumb dumbs. Why do people believe such nonsense as the bending of space? Crazy!

  73. ggzh a Argue With Everyone

    If the quantum multiverse exist, does that mean there is a version where i understand all of the video?

  74. Joshua Bonner

    You: Your rebel base is safe Me: Oh? What rebel base?

  75. xSorroWeaverx

    The multiverse does exist but not in the sense that every one thinks. You live currently in a multiverse continuously moving in between realities by the act of observation that becomes your current future and past. Like the double slit experiment that the current probability / "Chance" that the photon (your life) my end up. Making the illusion that there is a multiverse . NOTE that I said "You live currently in a multiverse continuously moving in between realities" At this point every decision/act/observation you make becomes your current state and reality and probability/ chance of future. The future is imaginably changeable but your past can never be changed due to the point of observation you are currently on.( Even if this was possible to travel to the past/ That point of observation will become your new past /present/future) The "Multiverse " is your current point of observation / In other words The multiverse is your current present and what you choose it to be :)

  76. GhostBladotetios

    How are we meant to save the nature of venus if we can't save our nature

  77. Bruno Teixeira

    This was the best explanation of quantum decoherence I've ever heard. Touché!

  78. Tomi Mikkonen

    Excellent explanation. There are interesting developments going on in quantum biology I heard. Wet and wam structures might be able to retain the coherence, thus explaining certain puzzling aspects of photosynthesis, entsymes and magnetic field navigation of birds. Maybe Stuart Hameroff and Penrose are onto something. (Would just like to find an explanation for something I experienced with DMT:-) )

  79. John B

    Even though the Downside to the human species, is that DOUBLE LOGIC exists within the human GENOME, there is a way around this problem, simply by DISCOVERING "The Processing System of The Real Self or LIFE".... This Processing System, does NOT contain DOUGLE LOGIC, unlike the human Primate.

  80. Matteo Simonetto

    What about the delayed choice quantum eraser experiment? In that setting the quantum particle being observed shouldn't be disturbed by any external particle. So why the decoherence is still there?

  81. Roger Blumenstein

    We can't even terraform our own planet.

  82. Jake Fields

    I totally misread the title as the aughra effect. Getting ready I was, speak to the gelfings I must.

  83. oldcowbb

    speaking to you goop lab

  84. Goddess Brahman

    Consciousness does not affect quantum mechanics. The decoherence obtains function in the states between consciousness - spirits. The incoherence is sustained because we live in a universe - not an omniverse. The soul sustains the incoherence between spirits in amounting to itself. An omniverse would be when we indiscriminately express consciousnes in our own internal universe, where no decoherence exist. The states connecting the soul in spirits omits this decoherence in the multiverse by the measure of unity absolutely. The invidivual measures of this is conscousness and it has no affect on reality, which quantum mechanics is the sensible distribution of. It only dictates our general direction in it, where the uncertainty principle applies. Go deeper, people. Almost there.

  85. Jerr Dnn

    Where is the episode on the spin network mentioned in this one? Plz and thx

  86. Daniel Bojidarov

    what if the big bang never ended and is still happening somewhere

  87. Joshua Bonner

    It bugs the sh** out of me that people refer to black holes into which things fall. A black hole is anything whose escape velocity is greater than the speed of light. It's not a hole into which things fall. Also, I've never seen a video talking about hawking radiation causing a black hole to revert either. If you had a black hole whose escape velocity was just barely greater than C and hawking radiation caused the black hole to slowly lose mass, then eventually, the escape velocity would be less than C and the black hole should revert. The basic laws of Physics dictate that information can't disappear from the universe so that implies that blacks holes can't be infinitely dense with infinitely small size which in turn implies that a black hole has a surface, albeit a surface within the event horizon.

  88. Nikolay Eftimov

    What about delayed choice quantum eraser experiment? The de-coherence cannot be caused by the detectors in the experiment, since the only difference between different paths is the ability to extract the knowledge of the which path information - everything else is the same. Can you elaborate on this?

  89. overthetop

    Nice presentation, however, the theory of the EM Drive relies on Special Relativity, not QM.

  90. Jarrod

    Ahh the good old _Schrödinger's Comment..._

  91. Lee Bloomquist

    entanglement = (measurement, entanglement)

  92. Dawit Moges

    8:20 I hate you

  93. Dawit Moges

    I'm delighted to not have everything go over my in I'm glad I get to understand 10% from 100

    1. Dawit Moges

      Ok I saw it 2nd time, I'm better now:)

  94. John Johnson

    Unfortunately we would be a waste of ammo.

  95. RF1204

    1 photon is one single sinusoide(of both B and H), my deduction. I read everywhere E=hυ is energy for One Single photon. And in the right side υ is some number of [cycle/s], so E(1photon) is J.cycle. More explanatory in the equivalent formula E=hc/λ, where the wavelength(λ) is m/1cycle. Like this half of quantum energy must be in the "positive" half of the H and B sinusoidal fields, and half in the "negative" (but respecting E much bigger than H, by Free space impedance (wikipedia) E=377H). The total power of this is the Poynting vector S=VH in W/m^2 == J/sm^2.

  96. Gabe Heller

    Wow that animation of a guitar string is really wrong. Waves don't move along a guitar string. The entire string moves up and down basically simultaneously (there are harmonics and I'm sure some delay that make it more compiex than that, but the fundamental generally overwhelms them) also as close as you show it getting to the fingerboard, it would be buzzy as heck. Also, to the best of one's ability one generally plucks the string in such a way that it vibrates more parallel to the guitar's surface than perpendicular.

  97. Bandofmodernbrothers

    If there are multiple histories does this mean there are multiple presents and multiple futures? Does this mean free will exists and this is proof of it, or is our present determined by the path of multiple histories that align to what I am doing in the present? If yes that means there can only be so many outcomes in my life before I become "in phase" again and align with my counter multiple histories in my opposite phase, (assuming at some point my quantum self went through a double slit). If my quantum self did not go through a double slit then it seems our lives are governed by a finite path of choices or multiple histories, which if I have free will I can choose my path in life along my multiple histories/presents/futures but my bigger path is set at one wavelength. I hope that makes sense, I am trying to link this to consciousness as if there are multiple ways and paths in the quantum world, surely this has an affect on my thinking in the macro world.

  98. Mike Z

    i wonder if this implies some sort of solipsism (everyone living in his/her own branch)?

  99. Ben Simpson

    So this is another attempt to avoid ourselves. First, we had defence mechanisms, then we had science, now, get ready for: SCIENTIFIC DEFENCE MECHANISMS! The best way to protect yourself against realising that you are the universe looking at and creating itself from pure awareness of your infinite nature! Brought to you today by PBS SpaceTime. * news bulletin outro *

  100. Arcatec MacArthur