Why the Big Bang Definitely Happened | Space Time | PBS Digital Studios


Our universe started with
the Big Bang, or did it? Let’s see how far back in time
we can push our certainty, and let’s see what
questions still lie beyond the limit
of our understanding. [MUSIC PLAYING] The Big Bang theory
was pretty contentious when it was first proposed, as
is any picture of reality that conflicts with
the current dogma. And I’m talking about both
scientific and religious dogmas of the time. However, these
days, there’s really no doubt that at some
level, the Big Bang theory gives an accurate
description of the earliest epochs of this universe. But how accurate? What part of this story
are we absolutely sure about and what parts are
still genuinely in question? Today, we’re going to talk
about the evidence that gives us so much certainty
for parts of the theory. We’ll follow with an episode
describing which bits are still highly uncertain, and possibly
even just plain wrong. I’m not going to spend a lot
of time describing the theory. There are so many great
resources for that, and we’ve linked some
in the description. Just the basics. The Big Bang theory is a set
of descriptions detailing the expansion of the universe
from a tiny, super dense, super hot speck to the enormous
cosmos that we know today. These descriptions are in
the mathematical language of physics, and they
build on and are supported by many experiments, from
astronomical observations to particle collider experiments
to supercomputer simulations. Some of these experiments
have verified certain parts of the theory beyond
reasonable doubt, while other parts
remain untested. Let’s start with
the irrefutable. The universe is expanding. Light from distant galaxies
is red shifted, stretched to longer wavelengths. And the further away
the galaxy is, the more its light is stretched. In the context of Einstein’s
theory of general relativity, the only sensible
interpretation for this fact is that space
itself is expanding and light traveling through
expanding space is stretched. The more distance traveled,
the more it’s stretched. The universe is
definitely expanding now. And so we know that
once upon a time, it had to be much smaller. See, this is the
wonder of physics. We can look at the current
state of the universe, or even just a tiny
part of the universe, and run the laws of
physics forward in time to predict the future. Or run those laws backwards
and predict the past. If we rewind the universe
using the mathematics of general relativity, then
the further back you go, the smaller the universe is. In fact, with raw
general relativity, we get that the entire
observable universe was once compacted into an infinitesimal
point, a singularity at time t equals 0, the hypothetical
instant of the Big Bang. Now, that initial
singularity is not something that most cosmologists
believe in. While general relativity
is incredibly successful, it doesn’t contain the machinery
to describe the quantum scale gravity of that first speck. So we know that at some
point in our rewind, pure general relativity will
give us the wrong predictions for the behavior of space time. But we understand those
limitations really well, and we know that we can be
confident in our predictions down to a certain point. For times after that
point, our understanding is good enough to make some
pretty bold and testable predictions about what
the universe must have looked like at various times. One such prediction is
that the entire universe was once as hot and dense and
opaque as the inside of a star. It was a searing ocean
of protons and electrons. A plasma. As the universe expanded,
this plasma cooled. And at a very particular moment
when the universe was around 400,000 years old and
about 1,000 times smaller than it is today, it hit
a critical temperature of 3,000 degrees
Kelvin, at which point the entire universe
slipped from plasma to gas as the first hydrogen
atoms formed. In the same moment,
the infrared light that had previously
been trapped in this fog was free to travel the
width of the cosmos. It’s still traveling
today, carrying with it an image of that early time. And we see it. It’s no longer infrared. Having been stretched
into microwaves as it traveled through
an expanding universe, it’s the cosmic
microwave background. We talk about it
in a lot of detail in this previous episode. So here, I just
want to emphasize that this ubiquitous radiation
is almost impossible to explain without a universe that was
once much smaller, hotter, and denser. So at least that
far back in time, the Big Bang theory is right. We see some amazing clues in
the image imprinted on the CMB. Firstly, it’s incredibly
smooth and even. But this mottled pattern
shows there are imperfections, tiny differences in temperature
of 1 part in 100,000 from one patch to the next. These represent regions where
there’s a bit more stuff here, a bit less stuff there. Very, very tiny fluctuations
that would let it collapse on themselves to
form galaxies and clusters of galaxies. That process, the
evolution from a smattering of tiny fluctuations to
a network of giant galaxy clusters, is also evidence that
the Big Bang picture is right. When we look to vast distances,
we’re also looking back in time and we see the
very first galaxies soon after they collapsed
from these blobs. Now, we expect them to be
violent places with galaxies colliding and merging
with each other, rich in the raw materials
of star formation but poor in the heavy elements released
by generations of supernovae. And they are. We see galaxies back
when the universe was 5% its current age. And they look very
different to galaxies today. The universe is
clearly evolving. But there’s another
amazing clue in the CMB. We see ripples of sound
waves in the pattern of those fluctuations. The fancy name is baryon
acoustic oscillations which cause ring-like clustering
of the CMB fluctuations. If the Big Bang theory is
right, then those ripples should have been frozen into
the distribution of matter at the moment the
CMB was created, and those ripples should
still be visible in the way that galaxies are
spread out on the sky. And yep. We see that, too. But all of this only gets
us back to 400,000 years after the Big Bang. We can rewind further. At an age of a few
seconds, we predict that all of the
universe was much hotter than the very center of
a star and remained so for around 20 minutes. During this time, nuclear
fusion raged across the cosmos, baking some of the
existing protons into heavier
elements in a process that we call primordial
nucleosynthesis. The Big Bang theory tells us how
long these elements were baked and at what temperature,
and so predicts the proportions of deuterium,
helium, and lithium that should have been produced. It’s in startling
agreement with what we see when we look out there. The Big Bang theory has
powerful, direct evidence, almost down to the first second. Although we don’t have
direct evidence for what the universe looks like
in its very first second, our understanding of
physics is still good down to a crazily early age of
10 to the power minus 32 seconds, when the entire
current observable universe was around the size of
a grain of sand, give or take. How can we be so confident? Because we’ve recreated the
conditions of the universe at this time. We’ve recreated
those insane energies in our particle accelerators. We can check that our physics
works in these conditions, and so we have a lot of
confidence in the predictions of that physics. However, this is where
our certainty ends. Earlier than 10 to the
power of minus 32 seconds, we just can’t
produce the energies needed to test our understanding
of physics in those conditions. But there are clues to
that earliest of times. Some are also imprinted in the
cosmic microwave background, and they may lead us back to the
instant of the Big Bang itself. We’ll rewind to the very
beginning of space time on the next episode
of “Space Time.” A couple of weeks
ago, the LIGO team announced the very
first detection of gravitational waves. We did an episode, and
you guys were all over it. Brendon Binns asks,
given this detection, is the “theory” of general
relativity still just a theory? Well, actually, it’s even more
solidly a theory than ever. In science, when
we say theory, we mean a description of
reality that has stood up to many, many experiments. We only call it
a theory if we’re pretty much certain that the
basic picture is correct. Theories actually contain
laws, and those laws are often the most
well-established parts of a theory. A theory may still
have parts that aren’t so well established,
but such uncertainties don’t invalidate
the overall picture. If they did, then we wouldn’t
be calling it a theory. David Mulyk points out
that it’s kind of weird that Advanced LIGO was
turned on just in time to catch the gravitational waves
from the merger of black holes. Very insightful. That almost as soon as LIGO
became sensitive enough to spot black hole
mergers, it spotted one. If these events were rare, then
yeah, it’d be pretty weird. But what if they
happen every few weeks? That’s actually the frequency
of detectable mergers predicted by some astrophysical models. And that’s about at
the midpoint between conservative and optimistic. If accurate, then
we’d expect to see one pretty soon after reaching the
necessary sensitivity, which we did. But that was months ago. Shouldn’t we then
keep seeing them? Shouldn’t we have
seen several by now? LIGO’s press release was
about the first detection. They didn’t say anything about
whether there’d been others. There have. But LIGO remains cautious and is
giving each detection due care. John Proctor points
out that the date cited for the discovery of this black
hole merger is September 14, and yet the official turn
on date for Advanced LIGO was September 18. As we mentioned in our
earlier video right after the first detection,
the rumor at the time was that the detection was
in the engineering data. There were eight
test engineering runs before the official turn-on
with the sensitivity improving each time as more and more
of the upgrades came online. The eighth run was at
full sensitivity right before the official turn-on. That’s when this
merger was seen, as soon as LIGO had fully
leveled up to the point that it was actually
capable of seeing them. To quote Lawrence Stanley,
“OK, but until the discovery of gravitational waves
can lower my mortgage and reduce the price
of gas at the pump, it remains just
a song that nerds sing to put their
kids to bed at night.” In other words, so what? It doesn’t mean anything to
anyone in the real world. But what a beautiful song,
I’ll be humming it to myself with the other nerds, as
these observations grant us stunning insights into the
fundamental nature of space time. I’ll still appreciate
the impractical beauty after those insights
allow me to ride my inflaton-powered anti-gravity
warp ship to the stars. At that point, I won’t be so
worried about the price of gas. [MUSIC PLAYING]


  1. Couldn't choose a sub so this'll work

  2. If the universe is expanding, what is the space it is expanding into?
    Is it the cosmos, expanding into an vast empty universe?

  3. Movement implies time exists. Think about it!
    It is more sensible that the singularity simply was. What I mean by that is that the make-up of the singularity was based on probability or an infinite position within the HB. That also explains how the energy was infinitely powerful and hence capable of infinite potential mass.

  4. Would it be possible for another Big Bang to occur within the existing
    Universe and if so what would happen ?

  5. Hubble Constant = change in wave speed

    ((c^7/(hbar*G^2))/(c^5/(hbar*G^2)))^0.5 = Wave Speed

    ((G / c) * (pi^2)) * (1 Mpc) = 67798.6421 m/s

  6. Time only counts when change can happen,before time or the seen Universe started there was no time which means no space,as we know it,what was on the outside of the speck that was in the singularity of the black hole our Universe came from,the sound waves caused by that explosion is now our gravity,today black holes cause "dark energy" while "dark matter' was created when our Universe was created to balance out what became light….what do you think?I think the dark matter is way more than any light as it takes less energy being dark and all,anyway it all has to do with sound waves more than you think,

  7. The universe is infinitely big. How dare anyone say they know the universe is expanding when we cant even observe 1% of the universe. We can merely observe whats going on in our neighborhood and we cant even grasp anything thats going on in said neighborhood.

  8. There will always be delusional retards, usually so bent on trying to promote their own desperate need to cling to their fairy tale stories of imaginary friends drawn from the only book they've ever read beyond Dr. Seuss. A theory is far more than simply an opinion as they would like to frame it, surviving the constant testing and predictions that one makes. And the more it goes without failing, the more certain it becomes as a FACT, whereas fairy tales requiring only faith and the need for a story that detracts from the fear of one's own mortality can be taken up by even the most ignorant as the truth, no matter how ridiculous it sounds to any educated person. Evolution of both the cosmos and life have both been proven as fact so may times that we can safely call them both science fact and just move on, but the religious morons will continue to ignore facts and pretend that calling the truth a "theory leaves it open for doubt.

  9. Physics is like sex: sure, it may give some practical results, but that's not why we do it. – Richard Feynman, in response to the last comment.

  10. The red shift proves nothing! Just an assumption. Science does not understand time and space so any "going back in time" is pure speculation.

  11. 2:08 The universe is not expanding due to red shift. Space/time thins out the farther from EArth you look because the origin of space is the earth itself if you consider that the universe is one big black hole emanating from Earth as the center. Light waves from galaxies far away does not implicate time either in such a black hole earth. All observations of the cosmos align with the idea that earth is a singularity/disc/spherical blackhole.

  12. 3:20 No known math describes T=0 as a singularity. A singularity isn't a time event in 3+1d spacetime, yet the big bang happened? Mathematics can't rewind to that moment or space, but it must exist? And most cosmologists don't agree on the singularity moment anyway? Cosmological fantasy.

  13. Okay, if I go with the fantasy of a "big bang" 14 billion years ago, now what? There is no way to get life to start!
    This video shows the absurdity of thinking that life could arise simply by chance! IT'S IMPOSSIBLE!

  14. If it's the space itself that is expanding how do we see it expanding at all? Doesn't my "metre rule" expand at the same time?

  15. I'm not religious at all and I am not so sure this is true. There is evidence against this theory. He presents this as fact. It is not.

  16. Please forgive me for my ignorance but if light from the invisible part of the universe reaches the visible part wouldn't this phenomenon be giving us the impression of big bang effect. In other words the sudden appearance of our universe may be an illusion. Has this being considered?

  17. Once again, where did this dense tiny speck that exploded come from? Who or what created it? If scientists can’t explain that then I’m not believing this Big Bang THEORY because that’s all it is, a theory

  18. Wait think about it. If the Big Bang was so hot then how could it create water if it did not evaporate it because it doesn’t make sense

  19. Nobody can prove the Big Bang REALLY happened. It’s a theory. And out of all the universe, which is huge, we have one little tiny planet 🌎 perfectly suited for human life. And all this happened from chance from some particle just hanging around in nothingness and exploded and here we are. That explosion not only created us and all life on earth, but emotions and thoughts and feeling and inclination towards good and bad. Ummmm ok.

  20. I lean towards science, but science once thought the earth was the center of the universe and was flat. How will the big bang theory hold up over time? (1000 years plus) We are presently dealing with dark energy and matter, so is there a chance at some point the big bang will be revised?

  21. My curiosity makes me wonder is the universe moving away evenly from us or is it moving faster in opposite directions from us?

  22. My curiosity makes me wonder is the universe moving away evenly from us or is it moving faster in opposite directions from us?

  23. Is a Big Bang even possible?
    Does mass /gravity suddenly turn explosive?
    Is there an example of mass/gravity suddenly turning off or switching direction ?

  24. If relativity only prevents information from travelling above the speed of light, could matter be passing through us above the speed of light all the time, with no force being capable of causing interactions at those speeds?
    In that case, there could be more than one universe and yet no disturbance at their point of meeting, if they're distant and fast enough.

  25. There was no practical application for the laser when it was invented, just because people don't understand how to use it now does not mean it won't have large ramifications for the future

  26. I'm just here for the comments especially those who claim to be Christian and can still believe in the big bang THEORY. I could point you in the right direction using the bible if you'd like.

  27. before and in the first nanosecond of big bang there was no physics, math, or spacetime so the equasion for it doeas not exist. So keep looking…

  28. Big Bang is explosion.Explosions tend to destroy things.It is not possible for explosion to create speric planets and earth that move in a harmonic way relatively to each other.

  29. You see this is why I don’t get some people. They have cars and gasoline because of discovery and the application of science. They’re literally sitting on top of a tower made from human endeavour, insulting the people who are building it higher. I don’t understand.

  30. Some people here are assuming that today's science is all about science. Unfortunately, nothing is further from the truth. Today's cosmology is extremely dogma driven, where any other idea is ridiculed and rejected. Most of what is in this video has NOT been proven SCIENTIFICALLY. Not the big bang, black holes (despite that altered photo), not dark matter/energy, neutron stars rotating, etc, etc, etc.

    But all of it is repeated in absurdum until they force you to believe it, with all the animations and artist renderings. Halton Arp proved that Redshift was more a measure of age and not distance (see his books). And together with other scientists, he stated that Big bang never happened. He lost his research fundings, his telescope times, and was finally fired from his university job. He was driven into exile to Germany, where he died in 2013. WHY? Because he would not retract his research and denounce his statements. That is why he was called The Modern Day Galileo (search that on YT).

    I always thought that science was the last bastion for humanity to stay strong and evolve. I've grown up since. Science is as corrupt and money-hungry as our politicians, if not more. Today's cosmology and archeology is NOTHING but Dogma, controlled by the big institutes and people who will NOT let the narrative change by new science. That would possibly cause them to lose their positions, incomes, and all the grant money. I know, crazy. Right?

  31. You have to be insane to think that all of the diverse universe came into being through an ignition and expansion. Where did the information to all that is come from? The design is all around you. You might as well cut your wrists and bleed out to get this life over with.

  32. We can’t even understand what came first the chicken or the fucking egg…. and people think they have answers to a universe from nothing! From nothing comes everything detailed down to an atom? Not to mention DNA ? Gtfoh

  33. After hearing all that no really knows and I love science. They can’t prove any of the Big Bang theory, sounds good but it’s no proof.

  34. Exactly this “nothing” is the biggest disadvantage of the Big Bang theory. Moreover, space-time is also expanding into “nothing” (“nowhere”). Thus, this “nothing”, by definition, should be a kind of non-material space-time, in fact, “dark space-time”. And the most important thing is that this “nothing” represents an absolute coordinate system, since it is in it, “in its space”, that the Universe expands (according to the Big Bang theory). But, according to the A. Einstein’s STR, this cannot be by definition, since there is no absolute coordinate system.

    Therefore, the very approach that the Universe “was born” from “nothing” (for example, from the Big Bang), or “expands” into “nothing”, is erroneous. From this it follows logically that the Universe is infinite in space and in time. That is, it (the Universe) has no beginning, and it has no end (this applies to both space and time). Otherwise, we will inevitably have “nothing”.

    The beginning “nothing” takes there, where the material Universe ends (for example, in the sense of space). It is the same with time: if there is a beginning of time, then there must be “nothing” in which time begins to flow (and which was “before time”).

    Therefore, our universe is infinite, that in space, that in time. That is, the universe has no beginning or end. And the dimensions of our visible Universe of radius h0 are determined by the finiteness of the speed of light (see the link Volodymyr Bezverkhniy's answer to What is causing our universe to expand and accelerate?). And if we move vast distances, then our visible Universe will also change: some galaxies will leave our species, other galaxies will appear.

    When depicting or describing the Big Bang, they usually depict the space in which the expansion of the Universe occurs (see pictures)….See more https://qr.ae/TWvGSh

  35. It wasn't the big bang… it was an eruption of matter / energy from another dimension. There are trillions of different dimensions , with old ones collapsing inwards building up unfathomable amounts of dimensional pressure causing huge black holes to open spilling or releasing pressure into either newly formed dimensions or older ones . The multi verse is surrounded by particle dark matter … that is all I'm willing to share at this moment

  36. Still peddling maths as reality. None of this can be correct. Theory is not fact. Precious little facts these days in science.

  37. For all of you, being sleeping for last 14 billion years, & being delusional about so called "BB" : https://www.youtube.com/watch?v=p8lKQMEYYLw …

  38. If the Earth's radius increases at 1 surface gravity per second, the Earth doubles in radius every 5.21 days. At that rate the known Universe would be the size of a proton just 2 Earth years ago. This means everything would be than again as small and not an explosive singularity, back in time. Are there any legs to this argument?

  39. So, if the Big Bang theory is definitely right, the Quantum Theory must be definitely wrong . I mean the wave function doesn't require a conscious observer in order to collapse after all. Or maybe I've got it all wrong and this is some sort of proof of the existence of some god ?
    Or maybe reality is just a story we tell ourselves on daily basis ?

  40. 3:50 at 400,000 years after it was ~1000 times smaller… I found that surprising given the size of the universe now.

  41. Perhaps this universe originated from a previous one. If that previous universe expanded forever under dark energy, then at some point it may have undergone heat death. In that case, maybe some tiny bit of it had just enough quantum uncertainly to blossom into our big bang. Now, I can't prove that idea, or disprove it; but that's my point. I don't think we'll ever be able to say what really happened before this universe began. There's simply no way to see (or calculate) into some past cycle. I doubt that even a true theory of everything will tell us that. Also – and I'm sure cosmologists have already considered this (though I never hear it mentioned): as the universe expanded, matter would have been carried along, of course. That makes me picture matter as stretching out & collapsing radially. In other words, filaments. Is this right? Thanks again. Rikki Tikki.

  42. It seems like the Universe once expanded to a point of thermal equilibrium is the same as the universe before the big band at thermal equilibrium. What about a Bose–Einstein condensate could it be state of matter at the point before the big bang at the end of that expansion?

  43. “…when the universe was a 1000 times smaller than today” But still infinite?
    Another thing that bothers me is all the talk about the fractions of seconds here and there. What was time like back then? And at what stage did the anti-matter do its thing?

  44. Did they come up with the 20 minutes to fit the data or did the 20 minutes come out of some theory? What holds the observable universe in the size of a grain of sand?

  45. Where did the three dimensional egg come from? The 3d chicken. And where did the 3d chicken come from. The 4d egg. But where did that come from? The 4d chicken! But where… You get the picture. Everything has has existence regardless of the number of dimensions. Adding more dimensions explains nothing!

  46. The expansion rate has never been measured as a function of the density (depending on the amount of matter or vacuum along a distance), or as a function of time (the scalar factor). As long as it is, the BB theory is a ad-hoc model to describe what is seen, but not what is not seen (dark matter, dark energy, anti-matter, vacuum energy, inflation and even creation of vacuum by expansion). Not surprising that the calculation of the expansion rate gives several results. To understand the cosmos, we first have to understand where GR comes from, otherwise we just do wrong extrapolations, as the Vulcain planet at Newton's epoch or epicylces before Copernic's epoch! Anyway, this theory is dying with the discovery of galaxies without dark matter, the age of the very first galaxies, and, in fact, it has died since the Tully-Fisher relation, and has died again with the Radial Acceleration Relation of Galaxies (expansion doesn't work without dark matter)
    would you please moderate your enthousiasm for a theory made with duct tapes?

  47. I still think it could be a space event that just happens like every 20 billion or ??.. like 2 black holes a galaxy and something else have to happen or something.. a large cluster of dense matter and energy

  48. getting a bit more insights to the underlying nature of the universe helps me come with all consuming existential crisis. so yeah, it helps us nerds to better sleep at night

  49. I bet that Lawrence Stanley would write the same "but it's impractical!" comment back when EM waves were discovered, and yet today he is able to send his comment to the whole wide world only because of the EM waves, back then he would have to use postal services!

  50. what does a thousand times smaller than infinity mean ? Also was the infinitely small initial state smaller than a planck length ?

  51. How was is shown that the universe (in spatial dimension) is expanding? Electromagnetic shifts (like red-shift) only shows that the source is moving away. So why did the big bang not happen in an already existing massive open and empty space? I want to know how it was proven that SPACE is expanding… Most of physics study "stuff"… How was it proven that "nothingness" is expanding. Just the fact that galaxies move away from each other, does not prove that what they are moving away into, is also expanding.

  52. 11:38 Fucking OWNED that anti-intellectual dimwit, in THE most epic way. Because, in other words: "SHUT UP! Our 'nerd song' (science) has given you everything you love in your modern life, and everything you just complained about… It WORKS and IT MATTERS!!! We 'nerds' care enough about improving the human condition, that we dedicate our lives to that pursuit! What do you do?"

  53. The Universe was created at a Point of
    Singularity through the Big Bang.The
    Energy is E=mc2.Where did that Energy
    come from.
    The Laws of Thermodynamics state
    that Energy cannot be Destroyed,but
    it can be changed from one form to
    another form.I know how the Universe
    was formed,and what was before it.

  54. Wait if we know it took 400000 years to light begin to travel and if we knew the speed the universe expanded during this period we would know how much universe exists beyond the obersevable universe?

  55. Okay. So the observable universe (~infinity) was once smaller than a grain of sand. That's pretty well noted with the physics and theories. My question, what else was there beyond that spec? More so, would whatever was beyond that spec be pushed away evenly in all directions as the inflation occurred? Could that single spec be creating a blast wave from the big bang moving the pre existing "world" or existence away from that center point? Could this in a sense have created a new existence within an existence which is pushing that existence away?


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