Time has a beginning?

[Tubbythin]

Why? At least that implies there has always been 'something' for something else to appear in, which sounds far more reassuring than at some point, everything 'popped into being' from 'nothing'.

I'm not saying I don't find the idea of time having a beginning a bit odd. I just find it less odd than the idea that something could have existed forever, personally.

 

[Aitch]

Be careful on that point, as it is often misunderstood. I assume you're speaking of the inflating-balloon analogy, right? If so, then take care to note that the universe in that analogy is the surface of the balloon, not the inside or outside of the balloon.

Badly phrased on my part - I wasn't referring to the balloon analogy (I was actually trying to imagine a three dimensional universe curving in all directions back in on itself in a four dimensional space - had to go and have a lie down afterwards ). However , in the case of the balloon it would be a circle drawn on the surface - that has an inside and outside. Which would have been what I meant if I had meant the balloon analogy. If you see what I mean.

 

[Perpetual Student]

So what indeed? Cesium doesn't exist in the early universe. How do you know that whatever physical processes are taking place then, there aren't an infinite number of periods before you get back to "t=0"? And how can you even know there aren't an infinite number of seconds periods going back to t=0, without knowing the metric? You can't.

Here is a quote from Wikipedia about the timeline of the big bang:

"Approximately 10^−37 seconds into the expansion, a phase transition caused a cosmic inflation, during which the universe grew exponentially. After inflation stopped, the universe consisted of a quark-gluon plasma, as well as all other elementary particles. ...
The universe continued to grow in size and fall in temperature, hence the typical energy of each particle was decreasing. Symmetry breaking phase transitions put the fundamental forces of physics and the parameters of elementary particles into their present form. After about 10^−11 seconds, the picture becomes less speculative, since particle energies drop to values that can be attained in particle physics experiments. At about 10^−6 seconds, quarks and gluons combined to form baryons such as protons and neutrons. The small excess of quarks over antiquarks led to a small excess of baryons over antibaryons. ..."

Now, the fact that there were no cesium atoms does not seem to prevent cosmologists and physicists from presenting this rather typical description of the big bang and inflation. Whatever "metric" is being used above is the same one I am using!

No, it's (what's north of the north pole) actually a rather precise analogy. As we discussed before, one of the several potential resolutions of "t=0" is the Hartle-Hawking instanton, which bears a striking resemblance to a hemisphere (only in 4D). Time is latitude on that hemisphere.

Well, precise or not, it is only an analogy.

 

[orange31]

To paraphrase the ancient star trek series, 'Bones, you're thinking like a human again."

If you consider time to be what it is - a dimension, or which we only directly observe four - it's quite easy to imagine a world without time, just like those models representing life in a 2-D world. The interesting part about the 2-D world models is how the flat space applied to a sphere is still a flat space to the inhabitants, but seeing how Euclidean geometry doesn't work anymore (ie, on a sphere a triangle has more than 180 degrees), the 2-D inhabitants can tell something 'else' is going on, even if they can't perceive the 3rd dimension of depth.

To me as a simpleton, it's similar to QM non-locality, where the math works but it cannot be 'visualized' in 4 dimensions.

 

[ponderingturtle]

The very concept of causality requires time. Can you say that about space?

There is so little difference though. Until you can know something about conditions before there was a universe, you can not say if there was time or not. I think there was likely something before the universe, but if that something had time as we understand it, who knows?

Mathmaticaly time is not that special, it is just another coordinate axis.

Until we know something about the conditions that gave rise to the universe we do not know if applying the concept of time as it exists in the universe is a meaningful exorcise.

 

[ponderingturtle]

Here is a quote from Wikipedia about the timeline of the big bang:

You know quoting wikipedia to a physcist is probably not the most authoritiative way to support your argument.

 

[sol invictus]

Now, the fact that there were no cesium atoms does not seem to prevent cosmologists and physicists from presenting this rather typical description of the big bang and inflation. Whatever "metric" is being used above is the same one I am using!

The whole point of this conversation - specifically, your OP - is that no one (not even wikipedia) knows what the metric was at very early times. Steinhardt and Turok would like to suggest a specific possibility - one totally unsupported by any experimental evidence, and probably theoretically inconsistent. You like that because you think it "solves" a "problem". Well, what I'm telling you is that there are many far simpler resolutions of that apparent problem.

One is that there is an infinite amount of time, as measured using the appropriate dynamics, between (say) 10^-37 seconds and "t=0". Without knowing the metric and the dynamics we cannot determine whether or not that is the case.

Another is that there is a finite amount of time, but we should excise the point t=0. Then causality in all three senses I mentioned is perfectly safe.

A third is that there is a finite amount of time, including t=0, but it makes no sense to ask about the "cause" of that single event (because as you yourself said, without time one cannot have causality; hence, the beginning of time had no cause).

A fourth is that time in the naive sense we think of it ceases to exist near t=0. I know several mathematical models for how that can happen; the simplest is the Hartle-Hawking instanton. I would say that unless some (unknown) dynamics prevents one from getting near the singularity, this is the most generic possibility. Both time and space believed to be quantities that exist and obey the rules we're used to only on average. When one gets down to very small size and very high energy, those averages cease to be even close to a good description.

A fifth is that there was indeed some kind of bounce, but it looked nothing like the one Steinhardt and Turok like so much (since in fact there is very little motivation for their particular choice).

I could probably think of more...

Well, precise or not, it is only an analogy.

That's because if I told you the exact model, you wouldn't be able to understand me. Therefore I'm forced to use analogies. I repeat - that particular one is very, very close to the true model.

 

[Cuddles]

While I am here, can anyone tell me what the limitations are on how far the Hubble telescope is able to 'see'

Well, firstly that's kind of a tricky question because the the expansion of the universe really messes with the concept of distance when you're dealing with sufficiently large, er, distances. So far the furthest Hubble has seen is the Hubble Ultra Deep Field, which looks back around 13 billion years. But it's not really possible to say how far that is, since the distance now is not the same as it was when the light was emitted, and there really isn't a sensible definition of distance for that kind of thing anyway.

That said, there isn't really any limit. Hubble, and all telescopes for that matter, are limited by the amount of light they can gather. If something is particularly bright, it will be seen from further away. The only hard limit is around 300,000 years after the big bang. It was at that point that light and matter decoupled and the universe became generally transparent to photons, so it would not be possible to see anything earlier that directly.

and these amazing photo's you see of 'horse-head' nebulae etc, are just computer rendered representations, right?

It depends what you mean by that. The photos are essentially the same as any other photo - they're just a pattern of photons gathered by a detector. Even the pictures taken in wavelengths invisible to humans are still just photos, they're just displayed so that different colours correspond to different wavelengths. If that's all you mean, then yes. However, I'm not sure the word "just" is really justified there. They're not computer models of what we think they look like, they're photos showing exactly what is there, just at wavelengths that we can't see.

In addition, Hubble is a bit different from many modern telescopes because it does actually look at visible light as well. for example, the Ultra Deep Field picture linked above is a composite of exposures taken at four different wavelengths, two of which are visible light.

 

[Perpetual Student]

For me, this has been a wonderful discussion. "The beginning of the universe" or "not" is an extremely important open question. I will continue to seriously pursue and think about this for the rest of my life. Although at times, I may give the impression that my mind is made up, that is quite far from the truth. It is only because the mainstream viewpoint of cosmology appears to favor a beginning that I take the opposite position (which I do favor) for discussion. Thanks to everyone for your thoughtful and insightful comments.

 

[blutoski]

To paraphrase the ancient star trek series, 'Bones, you're thinking like a human again."

If you consider time to be what it is - a dimension, or which we only directly observe four - it's quite easy to imagine a world without time, just like those models representing life in a 2-D world. The interesting part about the 2-D world models is how the flat space applied to a sphere is still a flat space to the inhabitants, but seeing how Euclidean geometry doesn't work anymore (ie, on a sphere a triangle has more than 180 degrees), the 2-D inhabitants can tell something 'else' is going on, even if they can't perceive the 3rd dimension of depth.

To me as a simpleton, it's similar to QM non-locality, where the math works but it cannot be 'visualized' in 4 dimensions.

The other part that some people have difficult accepting is that they're anchored on causality, and appear to be fixated on a unidirectional interpretation of causality.

Events are separated in spacetime, and very likely connected, but our direction is arbitrary. Time may not have started with the big bang - it may be ending there, and we're experiencing it in reverse.

Ah: [Retrocausality]

 

[Ragnarok]

The preponderance of the evidence points to a spot in the universe where time started.

That's what I thought, but I've also heard that no matter where you look in the universe we are still seeing more or less the same thing. That just doesn't make sense. Why would the distance we can see when pointing the Hubble in one direction, be the same if we pointed it the opposite way? Wouldn't that be like suggesting Earth is at the centre of the Universe again? How likely would it be that the the only thing that could determine it, was at the centre of our vast universe?

 

[theprestige]

"The beginning of the universe" or "not" is an extremely important open question.

Why? What's so "extreme" or "important" about it?

 

[RecoveringYuppy]

That's what I thought, but I've also heard that no matter where you look in the universe we are still seeing more or less the same thing. That just doesn't make sense. Why would the distance we can see when pointing the Hubble in one direction, be the same if we pointed it the opposite way? Wouldn't that be like suggesting Earth is at the centre of the Universe again? How likely would it be that the the only thing that could determine it, was at the centre of our vast universe?

Everybody on the surface of the Earth is 12,000 miles away from the opposite side of the Earth. Similar thing, one more dimension. The analogy is slightly off because we don't think we can see all the way around the universe, but everyone can see the same sized portion of the hypersphere that is the universe.

 

[Frankenstyle]

That's what I thought, but I've also heard that no matter where you look in the universe we are still seeing more or less the same thing. That just doesn't make sense. Why would the distance we can see when pointing the Hubble in one direction, be the same if we pointed it the opposite way? Wouldn't that be like suggesting Earth is at the centre of the Universe again? How likely would it be that the the only thing that could determine it, was at the centre of our vast universe?

Think of it like this,

Before the universe began to expand, all points in space were in the same spot. The distance between any two points was zero. As it expanded, the distance between any two points began to increase. So, since all points coexisted at the same place at the beginning, effectively all points in space equate the center of "the big bang". That's largely why the residual microwave radiation is so evenly spread, and why each point behaves like the center as you point out.

That's why if it were possible to circumnavigate the universe in, oh let's say in three days, it would always take three days no matter which direction you started off in, or where in the universe you started from. Don't get too literal on that sentence, I know I'm ignoring plenty of details.

Also it's a fair illustration to clear up the common misconception that the universe must have an "outer edge". I blame the balloon analogy for that one. People tend to add the space in the balloon, and the space outside of it, into an illustration that's only intended to use the surface.

 

[Perpetual Student]

Today, 03:12 PM #72
theprestige
Muse

Originally Posted by Perpetual Student
"The beginning of the universe" or "not" is an extremely important open question.

Why? What's so "extreme" or "important" about it?

Extremely important to me! You may be content to believe you are living on the back of an infinite turtle that was hatched from a big bad bang egg.

 

[Ragnarok]

Think of it like this,

Before the universe began to expand, all points in space were in the same spot. The distance between any two points was zero.

I thought before expansion there were no 'points', or even any 'space'?

As it expanded, the distance between any two points began to increase. So, since all points coexisted at the same place at the beginning, effectively all points in space equate the center of "the big bang".

Would the 'explosion' have had the same velocity in every direction, or could it likely have had 'bulges' in it, so that the expansion wasn't exactly uniform?

That's largely why the residual microwave radiation is so evenly spread, and why each point behaves like the center as you point out.

So you couldn't rewind the paths galaxies are travelling in and pinpoint where they all began?

That's why if it were possible to circumnavigate the universe in, oh let's say in three days, it would always take three days no matter which direction you started off in, or where in the universe you started from. Don't get too literal on that sentence, I know I'm ignoring plenty of details.
Also it's a fair illustration to clear up the common misconception that the universe must have an "outer edge". I blame the balloon analogy for that one. People tend to add the space in the balloon, and the space outside of it, into an illustration that's only intended to use the surface.

If there is no outside edge it couldn't be circumnavigated, could it? My understanding of the Big Bang is that the furthest reaches of the universe are moving 'outwards' from a fixed starting position billions of years ago and the Milky Way is somewhere between that 'starting position' and the 'furthest reach', and is still moving away from that 'starting position'?

Am I making any sense?

 

[Ragnarok]

I'm trying to imagine our position in the universe, as a small planet orbiting an average sun, somewhere on the fringes of one of the spiral 'arms' of the Milky Way galaxy.

This galaxy itself is meant to be rotating around a giant mass which some guess might be a black hole, isn't it? I know that the sun is orbiting some point within one of the MW's 'arms', but is our galaxy actually orbiting something, or is it moving in a fixed direction someplace?

As our galaxy rotates, are these 'arms' swirling away from the centre, or are they falling back inwards. Is our solar system eventually going to separate from this arm and drift into the massive voids between galaxies? Will our sun have died before that point?

Am I asking this in the wrong thread, or is it okay here?

 

[Frankenstyle]

I thought before expansion there were no 'points', or even any 'space'?

Sorta. I'm using "point" in a very loose sense, to indicate a condition of the universe when there was no separation between any two locations. Yeah, it's not really the right term, but at the end of the day I'm just trying to convey that everyplace and everything was in the same place.

Would the 'explosion' have had the same velocity in every direction, or could it likely have had 'bulges' in it, so that the expansion wasn't exactly uniform?

Well, for a long while we thought it'd be uniform. But there is a sleight ripple effect that allowed matter to coalesce...hold on I'm not going into it that far. Besides it sound like you're asking if it had bulges like a distorted balloon inflating unevenly. If so, you're thinking about it incorrectly. The Universe isn't like a balloon in the sense that matter is on the surface of the balloon, and as it inflates it moves away from a center point inside the balloon, and into the space around it.

The balloon analogy is meant to reference the surface only, and how all points on the skin of the balloon move away from each other as it expands. The surface is a two dimensional model of a universe, bent into the third dimension to illustrate a very simplistic visual aid for expansion.

So you couldn't rewind the paths galaxies are travelling in and pinpoint where they all began?

Sure. The further we collect images from, the closer we get to seeing that. Everything is moving away from everything else. Hit the rewind button, and everything starts moving toward everything else.

If there is no outside edge it couldn't be circumnavigated, could it?

Why not? I'm not being trite, I just don't understand.

My understanding of the Big Bang is that the furthest reaches of the universe are moving 'outwards' from a fixed starting position billions of years ago and the Milky Way is somewhere between that 'starting position' and the 'furthest reach', and is still moving away from that 'starting position'?

Not quite. The Universe is expanding, resulting in the distance between two points increasing. As time passes, the distance grows. Follow time back far enough, and you reach the spot where there's no distance between any two points.

*Things like time and "points" break down before you get there, so again I'm using the terms loosely-ish in the last sentence.*

The "fixed starting position" is any given point in the present Universe. Everything is literally moving away from everything else, not from "inside the balloon" toward the space outside.

 

[Ragnarok]

The parts I've snipped I understand somewhat, or at least have no questions about.

Why not? I'm not being trite, I just don't understand.

I thought circumnavigating was like following the circumference of something?

The "fixed starting position" is any given point in the present Universe. Everything is literally moving away from everything else, not from "inside the balloon" toward the space outside.

In that case, how are galaxies meant to collide? Surely if they were all constantly speeding up that should never happen? And if gravity is meant to be such a weak force, how could it slow down a galaxy?

 

[Frankenstyle]

I thought circumnavigating was like following the circumference of something?

Yes, but space is curved.

In that case, how are galaxies meant to collide? Surely if they were all constantly speeding up that should never happen? And if gravity is meant to be such a weak force, how could it slow down a galaxy?

We're talking about space expanding, not matter. And gravity is a weak force, but not impotent. It holds Earth in orbit, and summons asteroids to kill Dinosaurs. Heck, look up frame dragging, gravity even bends little kinks in time. Really what you're talking about here is more a case of the distribution of matter, which goes back to the ripples I decided not to get into a few posts back. I'll try to dig up a link for you on that one later, partly because I type too slowly, and partly because my own universe is collapsing right now due to the "irritated wife who thinks I'm ignoring her" effect.