# When is it real time

1. Dec 21, 2005

### stev

Is there ever a point in time that is actually the real time?

If we take for instance, midnight, which is usually thought of as 12:00. Is there ever a point in reality where the time is actually 12:00??? For there to be a point in reality which is 12:00, then 12:00 must last, or be, a certain amount of time - and in being so, it will no longer be 12:00 but 12:00 + the length of time it exists. Even if this length is minute (miliseconds etc.) there is no indivisible amount of time so surely we can get nearer and nearer the point of 12:00 then we were before but we can never get to it in reality.

Thus it stands to reason that, as 12:00 itself has no length of time, it doesn't actually exist.

?

2. Dec 21, 2005

### mathman

Why??????????????????????????????

3. Dec 21, 2005

### stev

Well if it doesn't, then when is 12:00?

4. Dec 22, 2005

### vaishakh

12:00 is an exact time as far as you are concerned. In that way your question is not clear enough to be answered. Anyway as far as present physics is concerned there is nothing such as absolute time.
O, I think you mean the length of time 12:00. Then I would have to ask you what is the length of a point lying on a line. If we move a little length from that point then the point where we reach is a differant point. So that way a point must have some length, may it be metre, centimetre or picometre.

5. Dec 22, 2005

### Renge Ishyo

Sure, there is such a thing as 12:00. The problem is that someone else might disagree about when it actually is 12:00, even if they are both trying to observe the same "point" in time. This is true even without special relativity, as very few people have clocks/watches that are perfectly synchronized with each other.

Last edited: Dec 22, 2005
6. Dec 22, 2005

### mathman

From a purely mathematical perspective, a point is 0 dimensional and has no length. If you move a point a tiny bit. you are creating an interval, which is a 1 dimensional thing and has a length.

7. Dec 22, 2005

### Renge Ishyo

Am I the only person that finds it humorous that this topic was moved into Philosophy?

8. Dec 23, 2005

### stev

"From a purely mathematical perspective, a point is 0 dimensional and has no length. If you move a point a tiny bit. you are creating an interval, which is a 1 dimensional thing and has a length."

This is what was confusing me - how can we say it exists if it is 0 dimensional and has no length? Time can never really be 12:00 and a point can never really be at 10cm?

Is there no amount of time that cannot be divisible? If not then what about the concept of reality being this split second, this instant, right now? As long as it lasts any amount of time that can be divided surely it isn't reality, it must be in the past. ie. if we say this very second is reality - isn't the second already in the past if it lasts a length of time?

9. Dec 23, 2005

### octelcogopod

Just because we are unable to perceive the present, doesn't mean it didn't happen.
Everything happens at the exact moment they happen on.
If that makes any sense.

A photo is a good example, it captures the "now" exactly as it was, and then we are able to look at that moment for as long as the picture lasts.
Don't confuse the human perception with the physical reality.

10. Dec 23, 2005

### Bob3141592

To have an experience of time the time must be of a certain duration, but that's a limit of how we experience things. The existence of an instant called 12:00 is independent of that. It's also a problem in how you label it. What you write as 12:00 looks like hours and minutes, implying any value of seconds in there is acceptable. I suspect what you really mean is 12:00:00.000.... In principle, it exists no matter how finely you divide the time unit (exclusive of quantum considerations). In practice you can only deal with a finite resolution of the time.

Isn't this somewhat akin to Zeno's arguements?

11. Dec 23, 2005

### Bob3141592

I'd also like to ask about where this instant of 12:00 occurs. I don't believe there is a universal "now" that exists everywhere at once, and the finer the time resolution, the closer the separation in space has tobe to agree on synchronization.

I only bring this up because of possible confusion in the application of "point" in "point of time."

12. Dec 23, 2005

### mathman

When you ask "where" you are raising a completely different question. Special relativity looks at this problem in great detail.

13. Dec 24, 2005

### stev

"What you write as 12:00 looks like hours and minutes, implying any value of seconds in there is acceptable. I suspect what you really mean is 12:00:00.000.... In principle, it exists no matter how finely you divide the time unit (exclusive of quantum considerations). In practice you can only deal with a finite resolution of the time."

Yes this is what I mean. For it to be exactly midnight, or exactly any point in time, it must be 12:00:00.000000000000000000(for infinity). But if this was the case then it would not last any amount of time because if it did then it would no longer be 0000000's for infinity.

"A photo is a good example, it captures the "now" exactly as it was, and then we are able to look at that moment for as long as the picture lasts.
Don't confuse the human perception with the physical reality."

I am probably wrong as I know extremely little on photography but I didn't think photos captured the exact instant of reality. Do they not just capture what appears over a certain time, and due to technological developments this time is now so small that it appears to be the instant of reality.

I know I am really wandering off subject now, but for our brain to sort out all the different colours and lights into objects and spaces must take a certain amount of time. Does this mean we are always living in the past?

14. Dec 24, 2005

### Renge Ishyo

You are correct, light does not travel to the photographic plate instantaneously. It travels very fast, at approximately 3x10^8 m/s (which is the fastest speed known), but that still is not instantaneous. A modern camera also captures light over a "range of time" because the shutter speed is going to be far slower than the speed of light. So light from many "exact instants" will get through in that window of time to expose the plate...this is why sometimes when you take a picture of something moving (such as a moving race car) the object appears "blurry." This is because the image/car has changed position and recorded a new position for light being reflected from the car in the time it took for the shutter inside your camera to open and close.

Does this mean we are always living in the past? This is a matter of definition, but I would say strictly speaking no (we are always living in the present). The past is defined as an area of time that can no longer change. The present is defined by constant change (and the future is simply what the present is going to change into). It may be correct to say that our visual sensors always *observe* the past (for many reasons we are lagging behind the present in our perceptions, the speed of light for one, and also the time it takes for that light to hit the receptors in our retina, to process that signal into an electrical signal sent to the brain, brain processing time, etc.), but this doesn't mean there isn't a present (and that we don't live in it and aren't affected by it). It just means we are unable to perceive it *exactly* as it happens because there is always a small delay as the information from the "instant" reaches us and is processed into our bodies (the "delay" between the present and the time when we take up the generated information just gets more noticeable the father away something is from us, like when we are trying to observe what happened in another galaxy for instance).

Last edited: Dec 24, 2005
15. Dec 24, 2005

### octelcogopod

Renge hit it on the head.
The delay between us registering the now, and it actually happening, is so small that we wouldn't know the difference (and we don't.)
Also, the current Now that we experience, can be defines as a now, even if it happens after the real Now, simple because we are experiencing it as now.

16. Dec 24, 2005

### stev

Could you compare it to the notion of the big bang:

So much (I really mean all) information is coming from this nothing point - that doesnt last even the smallest fragment of time - that we call reality.