Time has a beginning?

[MattusMaximus]

Due to these quantities being dynamic, it's generally not the case that the Hubble distance (to objects receding at lightspeed) is the same as the cosmological horizon. It's quite possible in general to observe objects that are receding superluminally.

Yup, many observed quasars with superluminal redshifts fall into this category.

 

[ponderingturtle]

Quantum mechanics and relativity are supported by countless experiments throughout the world. There is not one single shred of evidence that time had a beginning.

This is because people want to give special status to time. If you think of it as just another way in which events are seperated, and not too different from each of the spacial dimensions.

The north or north analogy is typical. Time might well have a begining, just like it seems space had a begining at the big bang.

What that is, is an interesting question, but how ever much you like or dislike it, it doesn't give you any evidence for or against it.

I do not see why a coordinate dimension like time can not have a starting point.

 

[ponderingturtle]

I've never really got why some people might find time having a beginning more repugnant than time not having a beginning. I find the idea that something could have existed forever much harder to get my head around.

The problem is can you have an effect with out a cause, and how can you have a cause and effect with out time. As it might not be possible to determine why the universe exists, this can be argued endlessly.

 

[blutoski]

Without time, there can be no causality.

Probably, but that may be what's called a 'local' phenomenon. Some experiments in quantum mechanics suggests that causality is not necessary for events.

So, if time had a beginning, how was the beginning caused?

It's credible that time exists independently outside our 3-spacetime framework.

(The way height intersects horizontal planes.)

 

[Perpetual Student]

All of the types of causality I mentioned in my post above were established. Let me ask again: if none of those are what you meant, what did you mean?

If time had a beginning, then time had to be caused, unless we accept that something can happen without cause -- which I do not. But for time to begin, it had to begin from timelessness, which is contradictory, since nothing can be caused without time.
Now, if one is willing to accept that something can happen without a cause, then the above contradiction does not occur.

 

[theprestige]

Now, if one is willing to accept that something can happen without a cause, then the above contradiction does not occur.

What if I'm simply willing to accept that something can happen without a cause that my mathematical model is currently capable of describing?

 

[Perpetual Student]

What if I'm simply willing to accept that something can happen without a cause that my mathematical model is currently capable of describing?

Well, I would ask if this is a one event happening or do things happen without cause sometimes, often or rarely? Then I would ask for evidence that these events do indeed happen without cause.

 

[theprestige]

Well, I would ask if this is a one event happening or do things happen without cause sometimes, often or rarely? Then I would ask for evidence that these events do indeed happen without cause.

If you're talking about the "beginning of time" then it's just the one thing: one mathematical singularity in the mathematical model that comprises our best understanding of time to date.

And we don't have any evidence that these things happen without cause. That's kind of the whole point.

The mathematical description of the cause is singular. It is undefined. In point of fact, we cannot describe it.

There could be all kinds of things going on "before" the point in time where our model gives us intelligible answers. But since the model can't describe those things, we can't really speak intelligibly about them.

 

[Reality Check]

If time had a beginning, then time had to be caused, unless we accept that something can happen without cause -- which I do not. But for time to begin, it had to begin from timelessness, which is contradictory, since nothing can be caused without time.
Now, if one is willing to accept that something can happen without a cause, then the above contradiction does not occur.

What you are saying is that you define that the beginning of time is an event, events have to have previous events in order to be caused and thus there is a contradiction since you cannot have "previous" events without time.

I would say that without time events cannot happen and thus the beginning of time is not an event and does not need a previous event to be caused. It is not that there is no cause - it is that causality is undefined.

There is also the Can causality exist without time? thread that demonstrated there is no mathematical problem with causality and a beginning for time.

 

[Perpetual Student]

What you are saying is that you define that the beginning of time is an event, events have to have previous events in order to be caused and thus there is a contradiction since you cannot have "previous" events without time.

OK, that also works.

I would say that without time events cannot happen and thus the beginning of time is not an event and does not need a previous event to be caused. It is not that there is no cause - it is that causality is undefined.

Well, I don't understand how the beginning of time is not an event. On the contrary, I would say, if time had a beginning, it was the most important event of all.

There is also the Can causality exist without time? thread that demonstrated there is no mathematical problem with causality and a beginning for time.

Yes, I participated in that discussion. The only thing that was demonstrated (in my view) is that time can contain an infinite number of causes and events even if time had a beginning -- a concept I struggled with for a time. But I do not agree that there was a convincing demonstration that there is no problem with causality and time having a beginning.

 

[Ragnarok]

I've never really got why some people might find time having a beginning more repugnant than time not having a beginning. I find the idea that something could have existed forever much harder to get my head around.

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'.

While I am here, can anyone tell me what the limitations are on how far the Hubble telescope is able to 'see', and these amazing photo's you see of 'horse-head' nebulae etc, are just computer rendered representations, right?

 

[blutoski]

If time had a beginning, then time had to be caused, unless we accept that something can happen without cause -- which I do not.

This is they key.

But for time to begin, it had to begin from timelessness, which is contradictory, since nothing can be caused without time.
Now, if one is willing to accept that something can happen without a cause, then the above contradiction does not occur.

That's correct.

 

[Reality Check]

Well, I don't understand how the beginning of time is not an event. On the contrary, I would say, if time had a beginning, it was the most important event of all.

Does an event happen at a time?
If yes then the concept of an event is meaningless when there is no time. This includes an "event" that is the beginning of time.

If no then there your definition of causality is flawed since events then have no order in time, i.e. events do not have related previous events.

 

[sol invictus]

If time had a beginning, then time had to be caused,

Stop right there. Why? Does space have a cause?

unless we accept that something can happen without cause -- which I do not.

No, that's wrong. There is no need to accept that anything happened without a preceding moment, any more than the positive reals have a smallest element. We already went through this.

There is nothing different about time going from -infinity to infinity and time going 0 to infinity - not until you've specified both the metric and the dynamics. As we already discussed, with a simple coordinate transformation I can map -infinity to 0. All of a sudden, time has a "beginning" (in your naive language), but all I did was change coordinates. It means literally nothing.

But for time to begin, it had to begin from timelessness, which is contradictory, since nothing can be caused without time.

What's north of the north pole?

 

[Frankenstyle]

If time had a beginning, then time had to be caused, unless we accept that something can happen without cause -- which I do not.

You're applying cause and effect to a state of the universe which "predates" (for lack of a better word) present physical law. Cause and effect were not yet "in effect", so there is no rule to violate. It'd be more reasonable to presume that the early universe began expansion because there was no other option available, than to dismiss the conclusions of a solid model simply because you don't feel cozy with the results.

The preponderance of the evidence points to a spot in the universe where time started. "Before" that point the model breaks down, along with physical law. Beyond that, the answer to "Why did time begin?" is as simple as "Because it could".

 

[Perpetual Student]

Stop right there. Why? Does space have a cause?

The very concept of causality requires time. Can you say that about space?
If you can, then I would suggest that the same argument would apply to space.

No, that's wrong. There is no need to accept that anything happened without a preceding moment, any more than the positive reals have a smallest element. We already went through this.

There is nothing different about time going from -infinity to infinity and time going 0 to infinity - not until you've specified both the metric and the dynamics. As we already discussed, with a simple coordinate transformation I can map -infinity to 0. All of a sudden, time has a "beginning" (in your naive language), but all I did was change coordinates. It means literally nothing.

This again? The metric is seconds of time as defined by the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. So what?

You can map any continuous period of time or length to countless things. For example, a length of one meter can be mapped to an infinite line from -infinity to +infinity. I don't think I need to show you a simple function to do that.
However, that does not make the length of one meter infinite, nor does it make an infinite line one meter long. In fact it says nothing about infinity or one meter. Your mapping is irrelevant.

What's north of the north pole?

This nothing more than a linguistic trick, and quite irrelevant to the discussion here.

 

[Reality Check]

This again? The metric is seconds of time as defined by the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. So what?

I know the answer to this:
You have quoted the SI definition of a second. That is not the "metric of time" which is the time component of the spacetime metric.

 

[Perpetual Student]

You're applying cause and effect to a state of the universe which "predates" (for lack of a better word) present physical law. Cause and effect were not yet "in effect", so there is no rule to violate. It'd be more reasonable to presume that the early universe began expansion because there was no other option available, than to dismiss the conclusions of a solid model simply because you don't feel cozy with the results.

The preponderance of the evidence points to a spot in the universe where time started. "Before" that point the model breaks down, along with physical law. Beyond that, the answer to "Why did time begin?" is as simple as "Because it could".

So there was a lawless, timeless state for the universe?
Since, as you say, the model breaks down, how can we say anything about the beginning of time? The problem is the model is not complete; reaching conclusions like "time had a beginning" is totally without foundation.

 

[Perpetual Student]

I know the answer to this:
You have quoted the SI definition of a second. That is not the "metric of time" which is the time component of the spacetime metric.

And?

 

[sol invictus]

This again? The metric is seconds of time as defined by the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. So what?

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.

However, that does not make the length of one meter infinite

That depends on what you measure it with.

This nothing more than a linguistic trick, and quite irrelevant to the discussion here.

No, it's 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.