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2 Futures Can Explain Time's Mysterious Past
cyberspittle sends this excerpt from Scientific American:
Tentative new work ... suggests that perhaps the arrow of time doesn't really require a fine-tuned, low-entropy initial state at all but is instead the inevitable product of the fundamental laws of physics. Barbour and his colleagues argue that it is gravity, rather than thermodynamics, that draws the bowstring to let time's arrow fly. Their findings were published in October in Physical Review Letters.
It was Back to the Future, Part II.
For those interested in time travel, the inaugural meeting of the International Time Travel Association will be held at the Perimeter Institute last Tuesday at 20:00.
The meeting location will be posted next Wednesday.
Can someone translate this for me (in American English) in four sentences or less what this is about, and more importantly - what it means to me?
I *refuse* to read science articles unless they are dumbed down, explained with barely-relevant images, and posted on medium.com!
I understand modern physics is quite far and I get that thing with Elephants but what are the turtles standing on?
The story so far:
The universe is increasing in disorder. Scientists want to explain it. So there are theories of thermodynamics, anti-gravity, anomalous pockets of order, and now gravity.
All these theories create the idea of a parallel or multiple universes. They also create a 'chicken or egg' condition as whatever created the proto-universe must stop and allow the disorder mechanism mentioned above to start expanding the universe. This new gravity-based theory is a half solution to this as gravity can create the proto-universe and an expanding universe.
in his book 'before the big bang' - he talked about the difference between thermodynamic and gravitational entropy within a system such as the universe. upshot: greater gravity = greater perceived order, while still following the rules of entropy. Ergo thermodynamics is just ONE possible engine of time. There are at least two we know of, and there may be more.
The actual scientific article was published on arXiv in september. Gravity does not appear to be central to the problem, it is just used as an example here. They basically look at a toy problem where a large set of particles with simple interactions give rise to solutions where they can identify variables that increase monotonically away from a minimum, and hence can be used as a time variable. It is basically an entropic argument worked out in detail for a simple system.
Carrol et al have published related ideas, and here is a popular science talk by Carrol (the main argument starts around 19 minutes into it).
Actually we can do better than that. The arrow of time is baked into fundamental particle physics and we have known this since the 1990's when an experiment, CPLEAR, showed that kaons turn into anti-kaons at a different rate than they switch back. This is completely independent of entropy and the result was further improved on by the Babar experiment only a few years ago showing that the 'T violation' occurs in B-mesons as well.
The article is wrong when it says that the laws of physics work the same going forwards or backwards in time. They do not and there is data to prove it. So the 'arrow of time' does not need any entropy to define it - it is baked into fundamental particle physics.
It was obvious that there is an arrow of time ever since it was discovered that we dwell in spacetime continuum.
Well, sort of.
There are infinite arrows of time, and each elementary particle possesses its own. The arrows of time are vectors of velocity in spacetime, and each one of those vectors has same magnitude, c.
Will knowing this further scientists efforts to create a working time machine or TARDIS?
If they're real psychics, they'll know I need their services and they can call me,
Entropy requires time in which to move to a more disordered state.
Time exists because entropy becomes more disordered.
Hmm. Spot the logical flaw there.
This idea is not new... they don't say it outright, but I believe they are suggesting "The big crunch" and the endless cyclical universe. Basically the Big bang was a point in a cycle. There was a universe that "Crunched" into a point like state and then exploded into our universe. But that other universe had time flowing in the other direction. If true, I suspect they're suggesting that the big bang was just one point in an endless cycle of expansion and contraction... though you should take care no to think that contraction is what you'd normally think of... Time is reversed so it would appear to us as just another big bang.
I heard about this theory as far back as the early 80s. It's a theory I always found theologically pleasing. It suggests the Hindi/Buddhists are onto something. ;-)
I've long thought that gravity and time are forces, like magnetism and electricity, and need to be unified.
I always thought this to be quite obvious once I though about it for a little while. ... I came up with this at about the age of 9. Since then I've been doing fine with that answer. Couldn't say if science found anything new, but I really don't care. That philosophical answer (I suppose it is one) is sufficient enough for me. :-)
You need space, matter and movement.
Those together create what we call time, when we observe it.
All four of those are interdependent.
We suffer more in our imagination than in reality. - Seneca
Ask yourself why time moves forward AT THIS SPEED. Why seconds?
Time travels forward in nanonseconds, milliseconds, seconds, hours, days, centuries. We perceive it moving forward in seconds because that is how our chemical brains record changes. If our brains saw x, then we'd see time as how far along x something is, whether it moved to the left or right x!
This is why we don't see the world move forward in nanoseconds, and can't enjoy the nano-detail.
Causality works forward and backwards, I can't kill my grandfather in +ve t, but equally if we travelled backwards in time. I cannot change the +ve time future.
Think about it, I move my coffee, the light catches it, the light hits my eye, I think of coffee. In backwards time, the beam must go from my eye to the coffee, and can only hit the coffee because I haven't moved it yet. We are on a stuck path and nothing can be changed, it has already happened, we only perceive it unfolding in forward time measured in seconds.
There is no arrow.
Comment removed based on user account deletion
If you are someone who researches the financial markets, there was a famous trader going back to the late 1800s named W.D. Gann. Gann's analysis of time was always that it was a subjective, illusory edge with respect to defining market movements, but that the definition was quantifiable at the highest of levels. In my book, "The Market is not Random.," I explore this subject more and think it is relevant for this conversation.
What's more, I think this article's timing is perfect with the recent theatrical release of "The Theory of Everything."
So, /. is time real or is it imaginary?
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artlu.net
It makes sense to me as two objects attracted to each other close the gap between them over time. The action of gravity supports the notion of time. It could easily be causal to the existance of time as well. Imagine two objects attracting in a system in which time did not exist. The joining of the two objects would be instantanious and violent.
...deperately in need of Occam's Razor.
No! The Hogfather, of course
Please hand in your geek card on your way out.
Because GP (and some physicist) think that if particle physics correctly describes matter/anti-matter....
Whoa there it is a LOT simpler than that. If you have a system in state A and it changes into state B then your process is A-->B. If you reverse time then the process you have is B-->A. Now if both these states have identical entropy there are no phase space arguments to favour one state over the other and so both processes (A-->B and B-->A) should be equally likely if the laws of physics are the same with regard to the direction of time.
What these experiments showed are that for some systems A-->B is more likely than B-->A and so the laws of physics define an arrow of time. If time were reversed then A-->B would become less likely than B-->A which is how you could detect it. It's the temporal equivalent of looking in a mirror. If you have a perfect left-right symmetry you cannot tell wether the image you are looking at is the real object or the reflection. However if the object is not left-right symmetric it is easy to know which image you are seeing.
So it does prove that there is an arrow of time. Perhaps you ought to spend a little time understanding the physics before you start applying simple logic: it tends to lead to more accurate conclusions.
Eggs turn into chickens at a different rate than chicken turns into eggs. This is proof either that A) time must go forwards, or B) my proof has a logic flaw in it.
Scale the system up, and they're just little birds that fly in boring ways, don't time travel, don't fly faster than light,...
Ummm...yes but the reason for that is because the fundamental physics governing the particles of which the starlings are made up prevent time travel and moving faster than light (which are actually one and the same). Assuming you are building a model out of simple, plastic lego bricks then regardless of what you are building we know that it will not be a conductor of electricity because the bricks you are building it from are all plastic insulators. Studying the fundamental physics of a system lets you know what is possible.
For example we know that there is a fundamental arrow of time despite the fact that at an everyday scale this is completely obscured by entropy. You could study all the flocks of starlings you like but it would be impossible to show that you have time reversal violations in it...and yet since the particles in that system are subject to the weak force we know that at some incredibly tiny, insignificant level it is there.
Entropy seems to accompany the expansion of space and the passage of time. At a future time and space configuration entropy will reach a maximum. Time will then stop and space disappear. The universe will instantly shrink to a singularity. The energy of the collision will carry the mass through the singularity in an inflationary big bang until gravity is able to gain control and the universe will unfold again.
I am not a physicist, but I have studied advanced physics independently. I never understood why gravity couldn't be the solution to time's arrow. I guess I am just a genius that nobody understands.