What is time?

[modest]

Originally Posted by Overdog

Could be. It seems we do have some innate sense of it, perhaps just because we remember the past, see the present, and anticipate the future.

Who knows. I'm not sure we'll ever know.

Would everyone agree that:

1. The past cannot be changed.
2. Anything that is spatially separated from us (at any point in time) we cannot currently (at that point in time) experience. In other words, the only things we currently (at one point or slice of time) experience are the things touching us.

~modest

[ldsoftwaresteve]

Originally Posted by modest

Would everyone agree that:

1. The past cannot be changed.
2. Anything that is spatially separated from us (at any point in time) we cannot currently (at that point in time) experience. In other words, the only things we currently (at one point or slice of time) experience are the things touching us.

~modest

The past cannot be changed. I agree. It can't even be directly perceived because it doesn't exist outside of our consciousness.

With respect to #2, the only things we can directly perceive NOW are the things that are affecting our senses now.

I'm not sure I accept the concept of a point in time, unless it is referencing a past or future now and we recognize that these concepts are internal references only, i.e. nothing outside of ourselves corresponds to these things.

Sorry modest if it sounds like I'm being pig headed about this. My problem is that we don't have a way of describing the nowness of now. To me, it's like the edge of the knife without the blade behind it. It has no width.

We timeslice a width that doesn't exist.

And by the way, excellent questions. Excellent trigger points.

[freeztar]

Originally Posted by modest

In other words, the only things we currently (at one point or slice of time) experience are the things touching us.[/list]
~modest

Ohhh, very cool, I like it!

The opposite seems just as true. We can not experience what we can not touch.

I'll go out on a limb here and say that based on the above, time is either something intangable, in which case we can not experience it; or, time is tangeable and we do experience it.

[Overdog]

I also agree the past cannot be changed, but have to agree with Idsoftwaresteve about #2, and also his point about those being excellent questions.

Freezy:

I'll go out on a limb here and say that...time is either something intangable, in which case we can not experience it; or, time is tangeable and we do experience it.

I'm not sure what you mean by tangeble, 1 or 2...

1 a: capable of being perceived especially by the sense of touch : palpable b: substantially real : material

2: capable of being precisely identified or realized by the mind

In my mind, I have no doubt whatsoever that I experience the passage of time, whatever that means.

[freeztar]

Originally Posted by Overdog

I'm not sure what you mean by tangeble, 1 or 2...

1a

[Overdog]

Well, in that case, we might experience it (definition 2) even though it is not tangible by definition 1

[Overdog]

Time is a word we use to help us assign meaning to the patterns we see in nature. Time can have multiple meanings depending on how we use it to understand things.

It is an abstraction of a pattern we see in nature. An intellectual construct. It is the way the human mind does things.

When we see patterns in nature and admire them, we call it Art.

When we see patterns in nature and describe them mathematically, we call it Science.

When we assign meaning to the patterns to gain understanding, we call it Philosophy.

Time can have different meanings depending on which way we are looking at the patterns.

Input from my wife.

EDIT:
She seemed a bit exasperated that all this was not plainly apparent to us!

[modest]

Originally Posted by freeztar

Ohhh, very cool, I like it!

The opposite seems just as true. We can not experience what we can not touch.

I'll go out on a limb here and say that based on the above, time is either something intangable, in which case we can not experience it; or, time is tangeable and we do experience it.

Interesting, but I think I used the wrong word when I said "things touching us". For example, if the sun suddenly vanished (Impossible, but stick with me) then we wouldn't see it happen for 8 minutes as it takes 8 minutes for the light to reach us. Similarly, earth's orbit around the sun wouldn't change until 8 minutes after the sun vanished. We can't touch gravity (presumably), but we still can't experience it at any given moment if we are spatially separated from "it". So, it's not really tangible/intangible I'm thinking, but rather what fundamental purpose time serves in our universe.

I might get some resistance by putting this in the language of physics, but I think it's best described with a lightcone:



described on wikipedia where the "hypersurface of the present" is outside our past light cone and therefore we do not experience it - we have no direct knowledge of it. I think this implies quite a bit about the workings of time and space. In particular, how our experience is limited to events not spatially separated from us. The further an event is spatially distant from us, the further in the past that event must be.

It's not hard to then conclude that without time, objects in space could have no notion of spatial separation. Everything would be an island with no meaningful notion of the rest of the universe. I don't think you need geometry to make that conclusion. As we're trying to make as few assumptions as possible, I think it's worth noting that our experience of things alone imply this relationship between space and time.

~modest

[freeztar]

Originally Posted by modest

Interesting, but I think I used the wrong word when I said "things touching us".

I found the use of the word "touch" philosophically profound. Photons "touch" our eyes. When I look at Mars, I'm not experiencing Mars directly, I'm "touching" the photons reflected off of it and into my vision. It then goes into my perception and is interpreted from there. Mars is tangible to me only by interfacing my optic nerves with the reflected photons off its surface. All other senses can be thought of in the same manner.

So, is time tangible?

[modest]

Originally Posted by freeztar

I found the use of the word "touch" philosophically profound. Photons "touch" our eyes. When I look at Mars, I'm not experiencing Mars directly, I'm "touching" the photons reflected off of it and into my vision. It then goes into my perception and is interpreted from there. Mars is tangible to me only by interfacing my optic nerves with the reflected photons off its surface. All other senses can be thought of in the same manner.

You've got a good point. Also, if gravity is an interaction of gravitons then it would be equally tangible.

Originally Posted by freeztar

So, is time tangible?

Certainly not - at least, I would think not. Time seems no more tangible than space (distance). I intuitively think of both time and space as descriptions of the universe rather than anything in the universe. Properties of the universe should apply to things in it, but not in a tangible way.

For example, describing the universe, I would say there are three dimensions (not counting time). That property of the universe applies to everything in it, but doesn't make "3 dimensional" a tangible thing that can be touched. It's just the way things most fundamentally are - 3 dimensional. The universe has this property time, and that property applies to everything in it. But, that doesn't make time something you can touch.

The way I think these fundamental properties of the universe can be identified is recognizing the "things" or "concepts" that apply to every situation and every thing. They are the things that have to be present to fully describe anything. If a photon hits an atom and ejects an electron and you want to fully describe what just happened then time and distance absolutely have to be in the description or you can't describe it. You could not simulate it on a computer without those variables. If a moon is orbiting a planet then you need space and time in the description. I can think of no real situation that is possible in our universe where space and time are not a property of what is happening.

Interestingly, it is possible to describe different universes by changing these properties. What if time went the other direction? Well, entropy would decrease over time. The broken plate on the floor would come before the unbroken plate on the table. That's not our universe, but it logically would work for such a universe to exist. What if there were 4 spatial dimensions? We can describe that mathematically and investigate what a universe like that would be like - but it's not our universe.

EDIT:

So, perhaps it all depends on how you look at it. If you define tangible to mean "the ability for two things to interact" and you don't put any constraints on those two "things" then you could logically conclude that 'time' is interacting with 'matter' and therefore a tangible interaction is happening. If, on the other hand, you define tangible in the more traditional sense as "the ability for mass to interact" then there is no tangible interaction happening.

It is, however, important to stress how real these non-tangible processes are. For example, if a photon is emitted in a distant galaxy and lands here on earth then something made the photon change on its way here. Its wavelength got longer and it lost energy. Did something tangible happen to the photon? Not really, but something real certainly happened to it.

On a side note, it seems incredibly difficult to use human definitions and human concepts to describe these things. They come with a lot of baggage. Describing the universe with math is so much more definite and applicable than with words like tangible and time.