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I saw this documentary hosted by Stephen Hawkins.

And if I didn't get it wrong, it says that there was no time before the big bang, time was created there.

So how can anything happen when there is no time (eg: the creation of time and the universe)? Is this what he calls a 'singularity'? Which I could think like this: when there is no time nothing can happen, except during this singularity.

Of course I don't know of a law that says 'when there is no time nothing can happen..', I just came up with it, as something intuitive.

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I think these questions are more philosophical than scientific, but I know many would disagree. –  Pygmalion Apr 19 '12 at 12:23
    
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I don't think anyone has any clue what happened before big bang. –  Pygmalion Apr 19 '12 at 14:32
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This question is meaningless in logical positivism, so it doesn't require an answer. –  Ron Maimon Apr 20 '12 at 1:12
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I did not watch that film (no time for this), but I suppose those words were probably used by Hawking in a mathematical framework and repeated by the makers, so do not try to think upon them. (If you do, it is going to lead to paradoxes.) –  Isaac Apr 21 '12 at 12:26
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6 Answers 6

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General relativity is a local theory. That means it describes spacetime near the point you're looking at but it doesn't say anything about the large scale structure of spacetime.

Now this may seem unrelated to your question, but actually it's key to why we say that time started at the Big Bang. If we make a few apparently sensible assumptions about the universe we can solve the Einstein equation and get the FLRW metric. This metric allows us to start at our current position and trace back towards the Big Bang to see what happens. As we do this we are calculating a geodesic, which is simply the curve in spacetime followed by a freely moving object. The key point about this is that from some point on our geodesic, e.g. me sitting typing this, we use the metric to calculate the immediately preceeding points, then from there we use the metric to calculate even earlier points and so on back in time towards the Big Bang.

The problem is that as we calculate back towards the Big Bang the metric gets larger and larger, and at the moment of the Big Bang it becomes infinite. You can't do arithmetic with infinity. It might be fun to speculate what $\infty$ times 0 is, but when this sort of expression crops up in Physics it means we have to admit we can't calculate what's going on.

This is why you'll often hear it said that time started at the Big Bang. It's because we can't calculate backwards in time from that point. Now that doesn't necessarily mean there was no time before the Big Bang, it just means we have no way of calculating it from General Relativity. If you believe Loop Quantum Cosmology, this predicts that there was a bounce at the Big Bang, so we can follow geodesics back through the Big Bang and into an earlier universe. However this is highly speculative.

Incidentally, you get exactly the opposite effect if you fall into a black hole. If you launch yourself into a static black hole your geodesic is described by a metric called the Schwarzchild metric. The metric allows you to calculate your path towards the centre of the black hole (the singularity) but when you reach the center the metric becomes infinite and you can't calculate it any further. It's often said that time stops at the central singularity in a black hole.

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Perfect, thanks. Only one thing: "Incidentally, you get exactly the opposite effect if you fall into a black hole". Shouldn't it be "exactly the same effect"? –  HappyDeveloper Apr 19 '12 at 14:38
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Well, at the Big Bang time starts and at a black hole singularity it ends. That's whay I said it was the opposite. However the two are mathematically very similar. You might be interested in math.ucr.edu/home/baez/physics/Relativity/BlackHoles/… as this covers this material and John Baez is an excellent writer. –  John Rennie Apr 19 '12 at 14:48
    
Nice reading, very interesting –  HappyDeveloper Apr 19 '12 at 15:21
    
I've amended my answer to your other question in the light of this one. –  John Rennie Apr 19 '12 at 15:28
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While technically half true (the FRW is singular), in modern physics we know about inflation, so this is false. –  Ron Maimon May 1 '12 at 14:36
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By matt Marsden...

I think you may find the problem here is in the question. Asking "How can something happen when time does not exist?" - implies that 'Time exists' and that 'Time is needed' for things to be able to happen.

Many people seem to 'assume' that time exists, and is 'needed' or 'passes' as things happen, but every apparent 'proof' of this I have read can be seriously questioned, and IMO, seen to be unfounded.

Direct observation of the world around us shows that 'things' exist, and that they can move, change, and interact etc where there is energy.

IMO careful consideration shows that direct observation of how the world around us exists and changes, does not actually prove or suggest, that extra to what we see, 'a past' or 'a future' or a thing called 'time' also exist. Although if we over extrapolate what we do observe, it can give a very subtle false impression, or 'illusion' that 'time' and in particular 'the past' exist.

As we walk around the world, we constantly change the contents of our minds.

That is to say, as matter exists and interacts around us, we see things moving and changing, and this changes the contents of our minds in a highly organised way.

And, we may 'CALL' some of these changed contents 'the past', and we may 'CALL' some of our imaginings 'The' Future, and from this we may (wrongly) assume that we have proof that 'THE' past and 'THE' future, and thus 'Time' exist.

And we may then assume that 'time is needed' for things to be able to happen.

But in fact, I think you will find things just exist and interact, or as Einstein suggested, but could not explain how, 'time... is a persistent illusion'.

In other words, while our 'memories' seem to point to or prove the existence of 'another' record of events called 'the past', it is not in fact obvious, or proven, that 'THE' 'temporal past' actually exists.

thus, for example, timelessly at great speeds (SR) or near a black hole (GR), things may indeed 'change more slowly' - but this doesn't prove that things happen more slowly because a thing called 'time' exists, and passes more slowly from an invisible place called the 'future' into an invisible place called 'the past'.

And note, we can't claim that...

A - 'everyone knows 'time is just a word everyone uses to describe all the motion we see',

and then also claim

B - The past and the future really exist, and 'time is also a real thing, connecting the 'past' and 'future' and Time is needed for things to be able to happen.

(And worse still, claim that 'everyone knows time is just a word', and then ask if we can 'warp', or 'travel through' Time etc).

Thus IMO it is invalid to say there 'would be no 'time' before the big bang', unless Hawking, or someone else has produced both 'a good reason to initially suspect Time exists', and 'an experiment that proves time's existence'.

matt welcome

(Author of 'A Brief History of TIMELESSNESS')

(Timelessness at the Greenwich Observatory)

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That method of saying nothing sure took up a lot of space. –  zhermes Mar 28 '13 at 2:01
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Our daily-life experience of time is different from what physicans think that time is.

Time is just some kind of additional dimension. Imagine our universe was 2-dimensional in space like the surface of a table. Now think of time a third dimension, that goes vertical up from the table.

Every snapshot in time of this 2-dimensional universe is a 2-dimensional plane parallel to the tables surface. All snapshots together give a 3-dimensional space-time.

Our "real" universe, that has 3 dimensions in space, can be seen as a 4-dimensional space-time.

Particles moving through space when time goes by are transformed to lines in this space-time.

But when we think of time in this manner, as some kind of dimension, then we lose things line movement, motion, cause and effect. And the universe seems to be an absolutely deterministic place, where everything is in its place "from the beginning" beause in this universe there is nothing that we could "feel" as time. But this is not true.

Laws of nature are able to describe a space-time like I described here that would be experienced like separate space and time for intelligent beeings inside this universe. So this is not a contradiction of time as we experience it in our daily life.

So this universe has no edges and boundaries in all of its space-dimentions, so it is endless in space. But it can have a boundary in its time-dimension. Think of the tables surface as this time-edge. The universe is everything above this table. Nothing INSIDE this universe can be below this table, because "time" below this table does not exist.

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It depends what you mean by 'cannot happen'.

Go back to a period before you saw that documentary, but not so far back time didn't exist, in ancient Greece there began a raging debate between Plato and his student Aristotle, about the nature of knowledge. Ultimately Aristotle's views gave us theories such as causation, and centred around observed behaviours, particularly in the natural world, and Plato spent his time thinking about generalities. The long and the short of this is that knowledge about things we can experience directly became known as physics, and that which we couldn't metaphysics.

As science advanced, and our knowledge of the physical universe increased, Aristotelean thought gave way to Newtonian mechanics, which gave way to Relativity on a cosmic scale and Quantum Mechanics on a micro-scale, however the divide between physics and metaphysics has not gone away, though the definition of what is physical and what is metaphysical has changed.

Originally 'physics' was stuff, and 'metaphysics' was information about 'stuff'. However, with relativity and information theory we know use the idea of a light cone. Since we know the big-bang happened, lets assume that at the first instant, photons of light began propagating out from the singularity at the centre of the big-bang, and continued to propagate out until today. If you look at this event in time, you see what appears like a ripple in a pond representing how far the light propagated out. However, if you look at this light propagation across time, you see a cone where the edge of the cone is the greatest distance the light has travelled since it first began across space and across time, small at first, but ever growing larger as time advances.

Nothing outside of this cone can be known to us, since light cannot travel faster than light. No information can be exchanged from events beyond this cone. In this view, physics would be all space/time and related stuff inside the cone of light that began with the big bang. Everything outside, such as additional universes would be 'metaphysical. We can think about them rationally, but we cannot obtain direct information. We can call this cone either a lightcone or an information cone.

Accordingly, since space and time began to exist the same instant, and since space and time are related, and since we are within the lightcone of space/time, we can study, poke, prod, test and derive information about space/time and things within, meaning natural or observable things, that act in repeatable testable ways. Things outside of this, however, we cannot study, as in observe directly, or experiment with. So to ask about conditions before there was time is not observable. That doesn't mean we cannot reason about it (so its not unreasonable), but it is not a 'scientific' question. So to ask what happened before there was time might be a philosophical question, perhaps even a theological one, but the fact is we cannot make scientific judgements about it, since science is the study of physical (meaning natural), not metaphysical things. We must make metaphysical judgements.

So lets try making a few reasonable metaphysical judgements: Every thing that has a beginning has a cause (we've not found anything yet that doesn't so it is repeatable and observable - to dispute this would be on 'faith'). The universe has a beginning, so it had a cause. The cause of the universe exists outside of time, so must be timeless. A cause that is timeless is eternal, so the cause of the universe is eternal. Every change represents a difference observed in time. An eternal cause outside of time, therefore, cannot change. Therefore the cause of the universe must be timeless and changeless.

etc.

To answer your question then, some event before time cannot simply just 'happen' since 'happen' presupposes time. However, it can be eternally purposed, realized as a historical event by a conscious observer, subsequent to the causation of time and space, from within the lightcone of this system. With respect to timeless, changeless causes - we have no scientific way of observing such things even if we can reason about them.

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Think of it as how we now know "our universe" is expanding and speeding up in expansion to the point of eventually there will be nothing around us and will only be able to see darkness, alone in our visible galaxy. Now seeing is how everything in "our universe" is a result of the after math of the Big Bang scattering everything outwards. Now to expand there would have to be already an empty space where everything we see out there is just fragments from whatever created the big bang in the first place resulting in the universe already existing in the first place. Now "time" is only relative to the perspective of "our universe" as to the creation of everything we can see and theorize from when it was created by the Big Bang but before, in and outside of "our known universe" to the furthest and last possible object that is still expanding, "time" is not actually what or when we think. Being as how something can not come from nothing relate back to the beginning of this of how eventually the expansion will leave our galaxy alone. Now being that there was space to expand into before our Big Bang, what made the Big Bang for our existence the reaction of two things to create this one single event. If the universe, not "our universe", is an unknown amount of space whose to say that we where the only Big Bang to happen. If we eventually expand so for away that we would never see the light of anything then how do we know that this has not already happened many times before in this infinite unknown space that is the universe. How do we not know that our Big Bang isn't the result of remnants of two other Big Bangs that happened somewhere in the universe, the empty space, again not "our universe" being that we think everything was created from nothing, and expanded to the point of being alone, where to finally meet and collide creating our Big Bang. With that being the said then time is not actually time but only the time we perceive and that what created our Big Bang had their own separate time that would have been perceived by the origin of their own existence.

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This answer feels like an incredibly long and incomprehensible sentence. Could you please try to structure it in paragraphs ?! –  Michiel Mar 28 '13 at 6:30
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I have seen the documentary, and this is what I understood after a few days thinking. If you are familiar with quantum mechanics, you know that particles of matter (electrons, for example) can appear out of nowhere. This happens everywhere and all the time in atoms, where electrons appear and disappear in ‘’random’’ spots around the nucleus. Since this phenomenon happens everywhere all the time, it thus is not against the laws of nature and physics to appear out of nowhere. We have the example with our electrons, which do exactly that all the time. Now, apply this knowledge to the Big Bang and the Universe in its whole. The Universe could have appeared out of nowhere, for no apparent reason, without violating the laws of nature and of physics. Time would also have ‘’materialised’’ at the exact moment of the Big Bang. It would have appeared out of nowhere, without any apparent reason, just like all the energy that was released and created (out of nowhere) at the Big Bang.

(Then again it makes you wonder if the Universe is not just an electron in another world…)

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