Before the Beginning of Time - Hawkings

[DaisyDay]

I didn't realize there could be a before...

The Beginning of TIme

 

[DaisyDay]

Well, this is disappointing, in a way...

Originally, I thought that the collapse, would be the time reverse of the expansion. This would have meant that the arrow of time would have pointed the other way in the contracting phase. People would have gotten younger, as the universe got smaller. Eventually, they would have disappeared back into the womb.

However, I now realise I was wrong, as these solutions show. The collapse is not the time reverse of the expansion. The expansion will start with an inflationary phase, but the collapse will not in general end with an anti inflationary phase. Moreover, the small departures from uniform density will continue to grow in the contracting phase. The universe will get more and more lumpy and irregular, as it gets smaller, and disorder will increase. This means that the arrow of time will not reverse. People will continue to get older, even after the universe has begun to contract. So it is no good waiting until the universe re-collapses, to return to your youth. You would be a bit past it, anyway, by then.

The conclusion of this lecture is that the universe has not existed forever. Rather, the universe, and time itself, had a beginning in the Big Bang, about 15 billion years ago. The beginning of real time, would have been a singularity, at which the laws of physics would have broken down. Nevertheless, the way the universe began would have been determined by the laws of physics, if the universe satisfied the no boundary condition. This says that in the imaginary time direction, space-time is finite in extent, but doesn't have any boundary or edge. The predictions of the no boundary proposal seem to agree with observation. The no boundary hypothesis also predicts that the universe will eventually collapse again. However, the contracting phase, will not have the opposite arrow of time, to the expanding phase. So we will keep on getting older, and we won't return to our youth. Because time is not going to go backwards, I think I better stop now.​

So, time won't reverse as space contracts. Darn.

 

[Halbhh]

I didn't realize there could be a before...

The Beginning of TIme

I had first read that article (actually the previous version, which has been modified some) several years ago, maybe 5. And again since. As I recall (perhaps imperfectly) off the top of my head, from a version (if it hasn't changed) one hypothetical idea Hawking incorporated was the idea of the laws of physics being communicated into our Universe via already being extant via imaginary time, a quantum mechanics dimension. So, 'before' real time (as we are familiar with everyday) began, imaginary time was already in effect. It's good to know though that you can find a lot of speculative hypotheses about how the Universe began, and the main thread of speculation lately is various versions of 'multiverse' hypotheses, which look to be likely forever untestable, no way to choose between disagreeing versions, likely. So one is left with a kind of faith act if one chooses one of the hypotheses and believes it likely. All of them already have passed the basic test of agreeing with known physics, so it's hard to imagine any kind of further test for them, but elegance and bayesian considerations, leaving one with in time various elegant competing theories which can't be chosen among except by faith. We want one of such theories to do something like predict a never yet observed phenomena, as did General Relativity, and then we can look for it and see it for the first time. That would be a kind of useful evidence. We don't have that, nor any other way to test multiverse theories.

 

[Michael]

I didn't realize there could be a before...

The Beginning of TIme

He's since updated his beliefs a bit.

Stephen Hawking thinks he knows what happened before the big bang

Stephen Hawking says he knows what happened before the dawn of time

It's kinda silly IMO to claim that time didn't exist prior to the big bang, and still claim that somehow something "changed" which resulted in a bang. It's ultimately an oxymoron. Personally I think his concept of "imaginary time" is a figment of his imagination.

 

[Monna]

I had first read that article (actually the previous version, which has been modified some) several years ago, maybe 5.

I am disappointed that the article is not dated. Does anyone have a date for it?

 

[Monna]

As "before" is an adverb of time, it (the word and concept) couldn't exist before time.

 

[Halbhh]

As "before" is an adverb of time, it (the word and concept) couldn't exist before time.

That's right. "Real time" of t=0 begins at a certain point. The 'before' is a kind of hand waving about the way the physics could be continuing from the imaginary time which was already in existence as best I understand. I haven't tried to go far into understanding that (I mean the math and all the parts), because there are so many competing theories.

 

[DogmaHunter]

We talk about "before" time, because we need to use language to communicate ideas. And our language kind of pre-assumes temporal conditions.

We don't have proper words to describe an environment where time or space (as we know it) doesn't exist.

How would you phrase the question "what happened before the big bang?" without using the word "before" in a way that makes sense?

Or how would you phrase the question "what caused the big bang?" without using the word "cause"? Because "cause" again implies temporal conditions. More specifically, a sequence of events: effects happen after causes.


I think it's fine to use those words as long as it is understood that in essence, the words "cause" and "before" are nonsensical in that context, but that we pretty much have use them due to the limitations of our language.


(this comment was written without watching the Hawkings clip and while not even knowing what he has to say about it)

 

[Michael]

That's right. "Real time" of t=0 begins at a certain point. The 'before' is a kind of hand waving about the way the physics could be continuing from the imaginary time which was already in existence as best I understand. I haven't tried to go far into understanding that (I mean the math and all the parts), because there are so many competing theories.

Guth talks about a "quantum flux" of some kind that set off inflation which does in fact imply change over *time*. All things have a cause, so the element of time would seem to apply to everything, including a 'bang' (assuming there was one).

 

[Michael]

We talk about "before" time, because we need to use language to communicate ideas. And our language kind of pre-assumes temporal conditions.

Something had to change/time for inflation to occur.

We don't have proper words to describe an environment where time or space (as we know it) doesn't exist.

Nothingness?

How would you phrase the question "what happened before the big bang?" without using the word "before" in a way that makes sense?

Beats me. As you note in your next sentence, I don't know how we could discuss "cause" without time either.

Or how would you phrase the question "what caused the big bang?" without using the word "cause"? Because "cause" again implies temporal conditions. More specifically, a sequence of events: effects happen after causes.

Bingo.

I think it's fine to use those words as long as it is understood that in essence, the words "cause" and "before" are nonsensical in that context, but that we pretty much have use them due to the limitations of our language.

How can you be sure it's 'nonsensical'. According to Einstein "spacetime' exists in the presence of matter and energy, and energy cannot be created or destroyed, so AFAIK any "bang" would simply be a conversion of energy from one state to another and "spacetime" has always existed because energy has always existed.

(this comment was written without watching the Hawkings clip and while not even knowing what he has to say about it)

That's ok. The issue goes beyond the opinions of one guy anyway.

 

[DogmaHunter]

Something had to change/time for inflation to occur.

Sure. But there it is: that's a temporal statement. We don't have language that can be squared with situations where space-time doesn't exist.
Whatever "happened", it's bound to be weird to us. How can it not be?

Physics of the early universe must be hard. You basically know in advance that you will have to come up with counter-intuitive ideas.

Nothingness?

Sure. If we define "nothingness" as "the absence of space time".
Which might make sense, if we define "existance" / "everything that exists" as "the universe".

But it's not clear to me (or anyone else, I would think) what one ends up with, if one removes "the universe".

How can you be sure it's 'nonsensical'.

I'm not. But what is known, is that space and time are properties/part of our universe. If you remove the universe, you remove space and time.

So time, as we know it, is no more.

According to Einstein "spacetime' exists in the presence of matter and energy, and energy cannot be created or destroyed, so AFAIK any "bang" would simply be a conversion of energy from one state to another and "spacetime" has always existed because energy has always existed.

Unless the total energy of the universe is 0, off course.
Then nothing needs any creating or destruction.

I've seen it explained once as saying that "out of 0, you can create +1 and -1. or +100 billion million and -100 billion million".

For the life of me, I couldn't repeat the technical physics stuff. But it made sense to me when reading it.

The general concensus either way, seems to be that at some point, the universe did not exist. If that's the case, then time as we know it didn't either.
Consensus also seems to be that T = 0 was a thing. So there's no "before" that. Whatever that means.

It seems as any way one wishes to approach this, it will be clouded in assumptions.
Which is kind of logical, since we have no confirmed origins theory for the universe.

 

[Michael]

I'm not. But what is known, is that space and time are properties/part of our universe. If you remove the universe, you remove space and time.

For the sake of brevity I'll just skip the things we seem to agree on. In order to remove spacetime entirely you'd have to remove all forms of matter/energy. As best as I can tell that would be "nothingness" but AFAIK, energy cannot be created nor destroyed, so energy and spacetime have always existed. The energy would simply have "changed forms" in any "bang" process. Since energy predated it however, spacetime also predated it.

So time, as we know it, is no more.

Sure, but only if energy can be created and/or destroyed, otherwise spacetime has always existed and simply changed forms from 'time to time".

Unless the total energy of the universe is 0, off course.

Well, it's not or we wouldn't be here at all, and "gravity" isn't negative energy in GR theory, it's simply a geometric curvature of spacetime like a hill that is caused by the existence/presense of energy/matter.

Then nothing needs any creating or destruction.

You'd still have to explain our use of energy over time in "zero" energy universe.

I've seen it explained once as saying that "out of 0, you can create +1 and -1. or +100 billion million and -100 billion million".

That essentially violates the whole concept of GR because gravity isn't energy in GR anymore than a hill or valley is energy. It's just a geometric feature. Even if you did that, you'd end up with an energy use over time that is not explained either.

For the life of me, I couldn't repeat the technical physics stuff. But it made sense to me when reading it.

Once you know even a little bit about how GR defines gravity as a geometry rather than energy (as in QM or Newton) it's not really very satisfying, nor is the concept of energy use over time. It's far more logical to assume that the universe is a net positive energy environment (which is how we use energy over time) and energy has always existed in some form or another.

The general concensus either way, seems to be that at some point, the universe did not exist.

Well the consensus is that it didn't exist in it's present form, but something has to have existed prior to this form, or there would be "nothing". There isn't "nothing", there's something.

If that's the case, then time as we know it didn't either.

Again, I think that's perceptual because the universe itself didn't exist, so time as we perceive it would have been different.

Consensus also seems to be that T = 0 was a thing. So there's no "before" that. Whatever that means.

That's like saying that a big bomb has a T=0 moment before it explodes, but the bomb had to have been built, so it's not not valid to suggest that time didn't begin until the bomb "exploded". It's convenient to describe a T=0 as the moment of explosion, but someone built the bomb and pushed the button to make it explode *before* it exploded (changed forms).

It seems as any way one wishes to approach this, it will be clouded in assumptions.

I certainly agree with that assessment.

Which is kind of logical, since we have no confirmed origins theory for the universe.

True. For all I actually "know" it may have simply always existed.

 

[FrumiousBandersnatch]

It's worth noting that when some physicists talk about the beginning of time they mean the 'arrow of time' (driven by increasing entropy), rather than a contrast with some kind of stasis where nothing can happen. At fundamental physical levels interactions are reversible, and there is no arrow of time - it's emergent at higher levels via statistical mechanics.

So it's possible to say that time (the arrow of time) started at the big bang, and yet still allow events 'prior' to that; i.e. stuff could happen, but with no preferred overall entropic direction.

That doesn't seem to be what Hawking is saying though - he seems to be describing a temporally closed but unbounded version, where as one approaches the big bang, time progressively undergoes Wick rotation into imaginary time (in the mathematical sense of 'imaginary'); I guess an analogy would be the way that, inside the event horizon of a black hole, time becomes a spatial direction and the future means being closer to the singularity (or whatever's down there).

From our perspective looking back in real (i.e. not imaginary) time, this rotation into imaginary time gives the appearance of a beginning; the suggestion is that this is an artefact of our viewpoint.

 

[FrumiousBandersnatch]

You'd still have to explain our use of energy over time in "zero" energy universe.

As you should know, using energy doesn't destroy it, it just converts it to a less useful form. For example, each relatively useful photon in the visible range hitting the Earth is eventually converted to around twenty relatively useless infrared photons radiating away from Earth, having done work.

That essentially violates the whole concept of GR because gravity isn't energy in GR anymore than a hill or valley is energy. It's just a geometric feature. Even if you did that, you'd end up with an energy use over time that is not explained either.

Not really; mass distorts spacetime, effectively putting energy into it; the gravitational field has energy. By analogy, when you put a weight onto a trampoline, the trampoline is distorted, storing energy.

As it happens, energy isn't conserved under GR unless you include gravitational field energy, so you can't have one without the other.

As Sean Carroll says in his blog:

The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.

... a lot of folks would want to say “energy is conserved in general relativity, it’s just that you have to include the energy of the gravitational field along with the energy of matter and radiation and so on.” Which seems pretty sensible at face value.

 

[Michael]

As you should know, using energy doesn't destroy it, it just converts it to a less useful form.

In order to 'use' energy you have to have some to start with. I'm also unclear how using and converting the energy that resulted in a big bang would have converted it to a "less useful" form.

For example, each relatively useful photon in the visible range hitting the Earth is eventually converted to around twenty relatively useless infrared photons radiating away from Earth, having done work.

Ya, but my point is where did the energy to create that photon and transfer energy and do work come from if not energy that existed prior to a big bang?

Not really; mass distorts spacetime, effectively putting energy into it;

It would take energy to put energy into something.

the gravitational field has energy.

Perhaps, but it's not "negative" energy. The sign is arbitrary in the sense that I could look at two distant objects and treat the distance between the two objects as a form of potential energy that converts to kinetic energy at the point of impact.

By analogy, when you put a weight onto a trampoline, the trampoline is distorted, storing energy.

In that case you're storing *positive* potential energy.

As it happens, energy isn't conserved under GR unless you include gravitational field energy, so you can't have one without the other.

I think that's a bit of misconception about GR based on the way "space expansion" and 'dark energy' are dealt with in LCDM rather than a function of GR itself. *Without* evoking space expansion or dark energy, how can you demonstrate that energy isn't conserved, or explain how it's not conserved? If I throw or hit a golf ball on the moon (assuming a pure vacuum), what energy is lost or gained when it lands back on the surface?

As Sean Carroll says in his blog:

No matter how you look at it, you're back to explaining the energy that is required to separate all the mass from what was presumed to be a "near singularity" thingy, and the use of energy over time. As long as you treat the energy as positive preexisting energy energy, it all adds up perfectly. If you start with nothing, you always have nothing and no energy to use to separate objects or to use over time.

 

[FrumiousBandersnatch]

In order to 'use' energy you have to have some to start with.

Obviously.

I'm also unclear how using and converting the energy that resulted in a big bang would have converted it to a "less useful" form.

Not sure what you mean; the answer probably involves entropy, but you'll have to explain what you mean.

... my point is where did the energy to create that photon and transfer energy and do work come from if not energy that existed prior to a big bang?

Nobody knows; I like the idea that something preceded the big bang.

It would take energy to put energy into something.

As Wheeler said, "Spacetime tells matter how to move; matter tells spacetime how to curve". The curvature of spacetime is in counterbalance to the energy of mass.

Perhaps, but it's not "negative" energy. The sign is arbitrary in the sense that I could look at two distant objects and treat the distance between the two objects as a form of potential energy that converts to kinetic energy at the point of impact.

You may feel it's arbitrary, but that's how it works - this may help explain:

The strength of the gravitational attraction between two objects represents the amount of gravitational energy in the field which attracts them towards each other. When they are infinitely far apart, the gravitational attraction and hence energy approach zero. As two such massive objects move towards each other, the motion accelerates under gravity causing an increase in the positive kinetic energy of the system. At the same time, the gravitational attraction - and hence energy - also increase in magnitude, but the law of energy conservation requires that the net energy of the system not change. This issue can only be resolved if the change in gravitational energy is negative, thus cancelling out the positive change in kinetic energy. Since the gravitational energy is getting stronger, this decrease can only mean that it is negative. [wikipedia]​

Your analogy is incoherent as stated - distance is not energy; and kinetic energy is the energy of motion which is converted to other forms of energy on impact. I recommend Physics 101.

In that case you're storing *positive* potential energy.

Yes; it was an analogy. The opposing forces cancel, so one could consider the energy of each to be working in opposition. Negative in the sense that each works in opposition of the other.

I think that's a bit of misconception about GR based on the way "space expansion" and 'dark energy' are dealt with in LCDM rather than a function of GR itself.

Fortunately, what you think isn't relevant; see the discussion of the “energy-momentum conservation” function in Carroll's article.

*Without* evoking space expansion or dark energy, how can you demonstrate that energy isn't conserved, or explain how it's not conserved?

See above.

No matter how you look at it, you're back to explaining the energy that is required to separate all the mass from what was presumed to be a "near singularity" thingy, and the use of energy over time. As long as you treat the energy as positive preexisting energy energy, it all adds up perfectly. If you start with nothing, you always have nothing and no energy to use to separate objects or to use over time.

Matter fields were the result of symmetry-breaking, which releases energy rather than requiring it. The use of energy over time is a question of entropy and the degrading of energy, as already explained. When you sum the energy of the gravitational field and matter, etc., treating gravity as negative, you get zero; so you don't need lots of energy to start a universe. YMMV, of course.

 

[Michael]

Obviously.

Not sure what you mean; the answer probably involves entropy, but you'll have to explain what you mean.

Nobody knows; I like the idea that something preceded the big bang.

Me too. It's a logical presumption.

As Wheeler said, "Spacetime tells matter how to move; matter tells spacetime how to curve". The curvature of spacetime is in counterbalance to the energy of mass.

That's more of a cause/effect relationship than a counterbalance per se.

You may feel it's arbitrary, but that's how it works - this may help explain:

The strength of the gravitational attraction between two objects represents the amount of gravitational energy in the field which attracts them towards each other. When they are infinitely far apart, the gravitational attraction and hence energy approach zero.​

Ah, well, that quote does explain his error. The attraction might be zero at infinity, but the *potential energy* is infinite, not zero. As the objects move toward each other, that positive potential energy is converted into kinetic energy. I don't have to do anything with gravity to turn positive potential energy into positive kinetic energy.
​

Your analogy is incoherent as stated - distance is not energy;

Sure it is. Distance is absolutely potential energy. If I start *on the surface* and a use energy to launch myself away from the surface, I store positive kinetic energy into positive potential energy in the form of distance. That potential energy is converted right back into kinetic energy when I come back to Earth.

Yes; it was an analogy. The opposing forces cancel, so one could consider the energy of each to be working in opposition. Negative in the sense that each works in opposition of the other.

But as I just noted, there's no need to even discuss the geometric curvature feature to describe distance as potential energy and show that it's converted into positive kinetic energy.

Matter fields were the result of symmetry-breaking, which releases energy rather than requiring it. The use of energy over time is a question of entropy and the degrading of energy, as already explained. When you sum the energy of the gravitational field and matter, etc., treating gravity as negative, you get zero; so you don't need lots of energy to start a universe. YMMV, of course.

My mileage obviously varies.

If you start with mass all clumped together in your near singularity bang thingy, you end up with a curvature around that singularity that will require energy to overcome. In theory that energy is found in the preexisting inflation field. It's easy to just treat the whole thing a positive energy from the start and then it all makes sense. There's really no need to treat curvature as a form of energy, it's just a geometric feature like a hill.

 

[joshua 1 9]

I didn't realize there could be a before...

The Beginning of TIme

God is outside of time, he has no beginning and He has no end. He is the Alpha and the Omega, He knows the end from the beginning. He writes the book of our life before we are even born. He has all of the plans. He give us our gifts, talents and abilities.

Gerald Schroeder - Articles - Age of the Universe

 

[FrumiousBandersnatch]

The attraction might be zero at infinity, but the *potential energy* is infinite, not zero.

Really? So when the gravitational force is zero the potential energy is infinite? Can you explain how that works?

As the objects move toward each other, that positive potential energy is converted into kinetic energy.

So, by your suggestion above, objects starting a large distance apart (gravitational force effectively zero) would have extremely large (though not infinite) potential energy, which would be converted into extremely large kinetic energy as they come together... So two pin-heads coming together a few light-years apart would eventually collide with the kinetic energy of, say, black holes colliding? If not, why not?

Sure it is. Distance is absolutely potential energy.

OK; so what's the value of potential energy per mile? How much PE in 10 miles, for example?

If I start *on the surface* and a use energy to launch myself away from the surface, I store positive kinetic energy into positive potential energy in the form of distance. That potential energy is converted right back into kinetic energy when I come back to Earth.

I can see what you're trying to say, but you're making basic mistakes.

The potential energy is not distance; it varies non-linearly with distance from the centre of mass, and is measured from an arbitrary zero point, so it can be positive or negative.

If you start with mass all clumped together in your near singularity bang thingy, you end up with a curvature around that singularity that will require energy to overcome. In theory that energy is found in the preexisting inflation field. It's easy to just treat the whole thing a positive energy from the start and then it all makes sense. There's really no need to treat curvature as a form of energy, it's just a geometric feature like a hill.

This is too incoherent to comment on.

 

[Michael]

Really? So when the gravitational force is zero the potential energy is infinite? Can you explain how that works?

Er, no. I should not have said that the potential energy is 'infinite' at an infinite distance, I should have said "maximum". That was obviously a very sloppy and oversimplified statement on my part. Sorry about that.

I'll just cop to that blatant error right now, and I'll skip your well deserved chastisement to save us both some time if you don't mind.

The potential energy is not distance; it varies non-linearly with distance from the centre of mass, and is measured from an arbitrary zero point, so it can be positive or negative.

True, but the greater the distance between any two stationary objects, the more acceleration they will experience as they are drawn toward each other. The velocity at impact will be greater with increasing distance, and the kinetic energy at the point of impact will always be positive. In effect, the distance between the objects ends up being a form of potential energy.

It would have been better for me to have simply stuck to the analogy of shooting a cannon ball or hurling something away from the planet. Whatever energy that I put into the cannon ball is going to be preserved at the point of impact (or air displacement in the case of resistance). There's still a conservation of energy occurring in that transaction.