Why Doesn’t Time Flow Backwards? (Big Picture Ep. 1/5)

Why Doesn’t Time Flow Backwards? (Big Picture Ep. 1/5)


The basic laws of physics – things like
F=ma, “gravity is inversely proportional to the distance squared”, Schrodinger’s
equation, and so on – don’t say anything about the direction of time. Sure, they relate what’s going on now to
what happens next, and to what happened previously, but there’s no distinction between forwards
and backwards in time. The past and future are on an equal footing,
as far as the microscopic laws of physics are concerned. In the macroscopic world, however, there is
one rule that does have time going in one direction only: the second law of thermodynamics. That says that any isolated system will tend
towards increasing entropy, or disorder. Like how cold milk and hot coffee mix together
into luke-warm coffee-milk, but will never “unmix”. Once a system gets to its fully-disordered
state — its equilibrium — there’s no more direction of increasing entropy to determine
the arrow of time. So the fact that we experience the flow of
time right now means that we’re not in equilibrium. There are basically two ways that could happen. Either the universe just happens to be, right
now, in this particular, low-entropy, configuration with two directions of time flowing out forward
and backward from it with increasing entropy in both directions; or at some point in the
far distant past the universe started with even lower entropy, and disorder has been
increasing ever since. [Spoiler alert: it’s option number two.] That low-entropy configuration was the Big
Bang. 13.8 billion years ago, the universe was hot,
dense, smooth, and rapidly expanding. A smooth dense plasma of particles might not
seem organized & low-entropy, but when the density of matter is extremely high, the gravitational
force between particles is enormous. Smoothness, in the face of such tendencies,
is not equilibrium, but is actually a very delicately-balanced, low entropy state. Things want to be gravitationally clumped
together into concentrated configurations like proto-stars, proto-galaxies, or even
black holes. What would a high-entropy, equilibrium universe
look like? It would be empty space. And indeed, that’s where we’re headed:
the universe is expanding and diluting, and eventually all the stars will burn out and
black holes will evaporate and we’ll be left with nothing but emptiness in every direction. At that point, time’s arrow will have disappeared,
and nothing like life or consciousness will be possible. The fact that our sky is decorated with billions
of stars and galaxies, and our biosphere is teeming with life, is a reflection of our
low-entropy beginnings. We don’t know why the universe started in
such an orderly initial state, but we should be glad it did: it gave us the non-equilibrium
starting point that’s necessary for the flow of time, as we know it, to exist. Everything that followed — from the formation
of stars and galaxies to the origin of life — has been a story of increasing entropy. Time’s arrow isn’t a deep feature of the
most fundamental laws of physics; it owes its existence to the specific initial conditions
of our universe. Hey, Henry here, thanks for watching. This is the first [second, third, etc] video
in a series about time and entropy made in collaboration with physicist Sean Carroll. The series is supported with funding from
Google’s Making and Science initiative, which seeks to encourage more young people
(and people of all ages) to learn about and fall in love with science and the world around
them, and the videos are based off of Sean’s book “The Big Picture: On the Origins of
Life, Meaning, and the Universe Itself,” which you can find online or in bookstores
around the world.

Only registered users can comment.

  1. Did you say time will eventually disappear? if so, it won't disappear suddenly but will vanish… then that means "time" will go slower?
    Great video btw

  2. I just want to understand better. Aren't there ways to decrease entropy? I know certain chemical reactions have a negative entropy (and although they are unfavorable, they happen). If we did that with the entire universe instead of a reaction, does that mean we would be moving backwards in time?

  3. Ерунда. Если бы время шло вперед, то оно бы остановилось относительно наблюдателя который так же идет вперед. Так что время на самом деле идет назад.

  4. Dude, if you're all for scientific credibility, then please don't treat the Big Bang like it's absolute fact. It's just a theory with lots of holes in it.

  5. Anything that is created is born in time and only moves forwards because it is created in a force of motion forwards

  6. Nothing can stop time the speed of light stops time relative because our measurement of time is a time moving relative to us

  7. I guess the more "technical" question would be, why does entropy have to increase? Why does our EXPERIENCE of time HAVE to match he direction of entropy in the first place? Yes, it's true that if I shuffle a deck of cards they will be in a state which is unshuffled. But if I play a YouTube video backwards, I can create a "digital universe" where there exists a phenomenon of shuffled cards moving towards a state of being unshuffled. Why can't there exist a universe where the laws of physics are reversed? For example, a universe where it is more likely energy will go from a low energy state to a high energy state instead of what our universe tends to do, which is to go from a high energy state to a low energy state.

  8. Well,if time runned backwards all allong,then we would consider it to be the standard time flow,considering it to be forwards…then our actual time flow would be the backward,if this ever happend

  9. I am scared! The universe will be empty? Someone please give a idea of continuing of biological life in that higher entropy or maybe simulate ourselves when that day comes.

  10. you could say instead of time flowing backwards, the laws of physics would be backwards. as in gravity would push things apart, the electromagnetic force would repel opposite charges, and pull the same charges. same with strong and weak forces. you just get opposite results. time would be as good as going backwards.

  11. So, is that to say that time will have stopped, or that it would be unnoticeable, because there is a huge difference

  12. The faster you go the slower time is.. so one galexy moving faster than ours means that tine is moving slower for the organisms in that galaxy than us. Plus. Why do we even care?

  13. Existence is consciousness itself. There is no such a thing as time. If you go far and long enough away from your conscious self, time looks like it moves from a to b. But it doesn't! Things are .. in the here and now.

  14. We have time travel figured out and managed to create teleportation but we still don't have invisibility cloaks WHAT THE FUCK FUTURE!?

  15. Why did the Big Bang happen if it was stable state? What the fuck why did matter exist like that, why did it just randomly occur and then explode? What?

  16. Maybe time does flow backwards, and we were actually meant to grow smaller and smaller until we vanish into nothingness.

  17. I love minutephysics so much, the only thing I find an issue is the "not even consciousness " could exist at equilibrium point you made. How are we to say consciousness won't exist being that we can't even grasp it as a world yet.

  18. Funny… these stooges can not even define time… and no, time can not go backwards. Just because you can "trick" math, doesn't mean it is real. Consciousness builds the universe in real time. We channel consciousness and that streaming is what we perceive as the passing of time… there is no going back, there is only NOW, and NOW=ETERNITY:)

  19. I do understand your way of thinking, but you`re wrong. As one in the comment says if Time goes backward we wouldn`t notice. As long as we can`t remeber the time going backwards, there will never be a solid prof. I think Time does either not exist or it is the 4th dimension. If it`s a dimension, then that means it doesn`t have a direction. It´s just a place like space. So if somebody asks for the time, then the thing he replies is the coordinate of time that the clock is in with the zero point at 00:00 last night. Even tho I don´t know that much about the Einstein theorie: If time is a dimension, then it actually makes a ltle more sense, that things don´t act at the same time relativly.

  20. don't remember how did it happen.. but i remember myself laying on the bed with my phone in my hands i had a 9am class on 7.3.18 and should have been late because i missed the alarm. Suddenly my background view got dark, i could only see numbers, minutes went backwards in non specific pattern, 2-3 min decrements, after approximately 20 min it stopped.. got to the lecture on time, even had a shower. Have anyone experience anything like it and how would you explain it?

  21. In 1-D mechanics, if you throw a ball and there are no other forces then it will continue in that one direction and not be able to turn back to its previous points. We can say that there is a direction in space that extends infinitely forward and backward, but the ball can never go backwards. But if you throw the ball (say upwards) and there is gravity (or some other force(s)), then the ball will go back to previous points. This is a force in a spatial direction.
    (And it doesn't matter if the force changes with time, the force vector has direction that is purely spatial.)

    So it seems to me that time will flow ever forward for all objects unless there is some force in the time direction. That is, there is an absence in forces in the direction of time. And somehow time got an initial push at the beginning of the universe and now there is nothing we know of to undo its present course forward.

  22. Donald Trump only learned about how powerful modern nukes are after being elected.

    Think about that for a moment.

  23. But why do humans, and seemingly all other animals remember the past, not the future? If our future selves exist just as much as our past selves, then why can we remember one but not the other? Is there something about memory that requires order or disorder?

  24. Time is just a concept- it’s not actually there, it is just a measurement that humans made up to make life easier

  25. Recollection – Anticipation
    There is no high, or low universal entropy. Only isolated states may be related to other isolated states. Universal Equilibrium is constant. You cannot compare a thing to itself.

  26. Why time only goes forward relative to each object? < Photon momentum
    This is an invitation to see a theory on the physics of light and time!

  27. You have no idea if we are headed for an infinite amount of time with empty space anymore than you know if we are headed for a Big Crunch, just like you don't know why the universe began in that low entropy state in the first place.

  28. Time doesn't flow backwards because of the uncertainty principle – particles cannot return to their past positions. Also if you want to mend a broken vase and reverse the damage to the vase you have to expend energy. For the universe as whole there isn't a "you" to do this  because you need reversing too.

  29. Gravitational force has no "-" in it's formula. The potential energy does (-GMm/r).

    Also, F = ma, a can be written as a = ∆v/∆t, ∆t = t2-t1. Due to that fact, we can see that the speed is decreasing if a>0, and we go backwards. So it does say something about time.

  30. John David Best has his web site Vida İnstitute. He put my articles page in 'Timeflow Theory' 'http://vidainstitute.org/?page_id=656'. Vida Institute is intersting site. And my web site is www.timeflow.org
    In your opinion, discovery of a planet is more exciting. Or, as I've presented in the attached article,
    whether observing 'A very tiniest mass in the space, having completed its life, have been turning
    into energy' would be more exciting or not ? It is my belief that, this observation will be the proof
    of the General and the Special Theory of Relativity. This observation can be made only by NASA or
    ESA. I hope that I will be able to see this consequence while I'm still alive.

    Sincerely

  31. Some misinformation in this video that needs to be corrected. The Big Bang was not the "lowest entropy" state of our local universe. That existed inside of the Super Black Hole at the moment before it destabilized and then exploded to release its accumulated energy and mass so they could give birth to our present expanding Big Bang local universe. However, our visible local universe is not the only one in existence. All of the infinite space of the cosmos is filled with an infinite number of other local Big Bang universes all expanding as does ours now.

    At some point in the future, perhaps a hundred billion years from now or more, the outer expanding surface galaxies of adjacent local Big Bang universes will begin to collide with each other throughout the infinite space of our cosmos. At that time the entropy of the cosmos will be at is maximum. These colliding dead galaxies' burned out stars, under the influence of mutual gravitational forces, will coalesce, accumulate, and then form an infinite collection of growing Super Black Holes spread out across the infinite space of the cosmos. It is during this time that the entropy of the entire cosmos gets automatically reversed and brought back to its starting point.

    When all of the energy and matter outside of the infinite number of growing Super Black Holes is finally absorbed into them and passes through their event horizons, then the cosmos will be ready for Rebirth and a natural process will begin to occur in all of the central bodies or "singularities" of all of the infinite number of Super Black Holes which will cause them to destabilize and, perhaps after only a ten billion years or so, more or less simultaneously detonate in an infinite number of Big Bangs that will then the fill infinite space of our cosmos with an infinite number of local expanding Big Bang universes again.

    This process had no beginning in time, is occurring now, and will continue to happen into the infinite future. It is the order of things. It is the only thing that can exist and, indeed, must exist. No conscious life's effort in the cosmos can do anything about its directions of entropy changes and time flows on the infinite level, but, perhaps, with enough advanced technology it might be possible to affect things on a small local scale; that is, it might be possible to prematurely reverse the entropy of small parts of the cosmos in a laboratory environment using special equipment and processes. Thus, we would be able to make cool objects spontaneously heat up, springs spontaneously expand or contract, clocks run backwards and their mainsprings tighten, old organisms become young again, water run uphill against gravity, and scrambled eggs unscramble themselves. This would all happen without any compensating increases in entropy occurring outside of the region of space of the cosmos in which the special equipment was causing entropy and "time's arrow" to reverse direction.

  32. This is not true. Although some physicists theorize that the second law of thermodynamics results in the forward flow of time, we don't actually know. This video presents it as if it's fact, which it's not. It also draws nearly the same picture half a dozen times.

  33. Someone should make a BTTF like movie in which time starts going backwards Maybe because "doc" screwed up the universe with his time travels and "marty and doc" are not effected by this and have to make sure time goes forward again…

    I can already hear doc say:"thats because you are not thinking in 4 dimensions"

    I love bttf im srry

  34. I agree that thermodynamics necessitates a big bang with low entropy, which matches our understanding of the universe's evolution and the ability for life to evolve. However, I don't agree that this is the definitive source for time's arrow. Even if you had a soup of particles in equilibrium, being in equilibrium means just having maximum disorder. But the particles in that soup are still moving around and bumping into one another, each one of them following the system's equations of motion, despite them all being in equilibrium. So this argument, while interesting, can't explain why there's a perceived arrow to time in the first place. In fact, according to general relativity, the flow of time shouldn't exist at all regardless of the initial conditions at the big bang because time is just a dimension, one of the four dimensions in spacetime. So the flow of time itself seems to be an illusion (see Brian Greene for more on that). I think it will require some nontrivial understanding of human consciousness in order to explain the arrow of time, and perhaps it's related to entanglement (quantum complexity). However, I don't think simply excusing it away to the big bang's initial data is sufficient.

  35. Wait… How can energy be evenly distributed throughout a (theoretically) infinite universe to reach equilibrium? Or perhaps this suggests a finite universe?

  36. 0:15 but time symmetry tends to break, as could be seen in fundamental particals such as quarks which are bound by strong nuclear force, for ex- two different quarks can switch places with each other however the time taken by each particle switching places is different, hence time symmetry do tend to break down (but not s-p-t symmetry). By this, we can differentiate between past and future, so there "can" be a distinction in time under certain circumstances in microscopic world. Just my two cents.
    Edit – Pardon my grammatical errors, if any. English isn't my native language. Thank you. 🙂

  37. So I guess this rules out the Big Bounce Theory. Or at the very least means this might be the last bounce…. but maybe we aren't even able to make proper predictions yet since we can't see beyond the observable universe, just as before telescopes, we thought the Earth the centre of the Universe.

  38. Thw World today is mirroring this exact thing! Things are speeding up too fast,becoming dis-ordered and chaotic,heading towards nothingness….Thanks Liberal Democrats!

  39. Ok, so in essence once the universe reaches an equilibrium then all time will stop and everything will come to a stand still, yes? It's a bit frightening to think that I could be driving my car down the highway one moment and then in the next suddenly my car and everything around me including myself and all my constituent molecules/atoms/quarks will come to a stop and so to will the planets rotation and the solar system/galaxy's movement through space… Then again one could never realize what has happened without having the passage of time to think about it. Of course that's not how things work. As long as there is energy within a system there will be motion. But since energy can neither be created or destroyed (only converted into matter)does it not stand to reason that there will always be energy without our closed system/the universe? So in essence a equilibrium can never be reached and time will never stand still? But if our universe is a close system then it must eventually reach an equilibrium. Which leads one to conclude the universe is not a closed system. Furthermore, if the universe had a beginning would it would be reasonable to assume it will have an end. But how could the universe have a beginning in the first place? It couldn't have possibly come into being out of nothing…

    Are these conclusions erroneous? And if so in what way(s)?

  40. No. The future will not be at equilibrium. Fundamental laws of the universe are constant but the sub rules (such as the human brain neural network) are always changing which forces a circular loop of interacting sub rules.

  41. He might as well be reading from a fifty year old text book. Since those brave pioneering days, it has been discovered that the mathematics of Relativity are the same as those used for thermodynamics, while one researcher has even documented time flowing backwards on macroscopic scales using a micron sized polystyrene bead suspended above a heat bath by optical tweezers. In fact, this year the first thermal diode, or Maxwell's Demon, was invented that can pump heat from a cold source to a hot one, without expending any energy in the process. Another recent development, was the first evidence constraining quantum thermodynamics to two dimensions, implying that even the definition of heat and time are vanishing down the nearest convenient rabbit hole or toilet of your preference, because 42 is as good as it gets. If change is the only constant, its only because, if it were any different, nobody would be around to ask the question.

  42. But how do we know time doesn't go backwards and start moving forward again…. Going backwards would also mean everything is "undoing" itself including our memories and then it starts moving forward again and we have no idea…. All these laws are what we observed in universe, including this entropy law. But I don't think we can know for sure if time goes backwards or not because we won't remember it happening….

  43. I think time is a direction (like left or forward)
    But not a direction we can perceive. The universe is moving or expanding in that direction just as it is expanding constantly in length, breadth and height.
    [our universe has four dimensions: length breadth height time]

  44. Quick question: are those two options actually different or can they be seen as representing the same timeline at different scales? That is, Option #2 just looks like a zoomed in version of Option #1.

Leave a Reply

Your email address will not be published. Required fields are marked *