h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I'm also asking at the Forum, just to get a different set of answers. Something more than yes or no would be good.

Absolutely. All of physics - classical and modern - is predicated around the existence of time (although the definition gets tweaked as you move from one to the other). And, at least in a self consistent way, all the experimental/predictive success of physics confirms it's existence.

Actually, we really want Noggin and Gnomon to answer this question, but I'll provide what I can of the experimental side of things until they arrive.

You have the major principle conservation of energy. 1 joule of energy is defined as being what it takes to accelerate a 1 kg object at 1 meter per second squared for a distance of 1 meter. This principle gets applied/used in so many fields this day, that can be taken as support/further verification that time exists.

Of course, could there be a system which somehow mixes the definitions of mass, time, and distance in a different way? Yes! In fact, it seems that general relativity does just that. Does that mean time doesn't exist? That depends on your definition of "exists". I think in some form or another it does.

Yes, but it might be a lot stranger than we think.

To start with, in modern theoretical physics you already have strange effects like reverse causation, particles travelling backwards in time, etc. A friend of mine who works in this area tells me that they think that the next big breakthrough in theoretical physics, marrying general relativity and quantum theory, will involve a new conception of time that will have to be quite radically unlike our current conception (in much the same way that Einstein's conception of space was radically unlike Newton's).

I can't tell you more than though.

A lot depends on how things are conceptualised/defined.

Take reverse causation. By *definition*, effects come after their causes. If there are two states that are causally related, the one that comes after *is* the effect. So would we be talking about "folds" in time, rather than reverse causation?

If particles are "travelling backwards in time" does that mean that the past is continually changing, or that the future already exists in a fixed form?

"Time is the form of inner sense." Immanuel Kant

Noggin

Can I put this in stupid for a second?

I read once that "that which can not be measured does not exist". I had a problem with it then and still do, but thinking about the tree in the forest helped.

Tree falls in forest, nobody (living being, recording device) around, does it make a sound? No, because the vibrations of air caused by its falling have no eardrum or other membrane to reverberate against, with which to be interpreted as sound.

That's how I get it with time. For there to be time there has to be an entity present to recognise it as such. Wipe out all life in the universe and (presumably) things would still happen - planets would orbit stars, stars would orbit galaxies - but the process would mean nothing with no-one for it to happen *to*.

That was simple. Where's the stupid?

Noggin

I'm never particularly confident in these sorts of discussions, especially in the company of people comfortable talking about anti-matter, gluons and bosons, and All That Sort Of Thing.

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Actually, I never even finished secondary (high) school physics, never went to university, and don't understand maths. Just fake it.

Noggin

Does time exist? No. And treating it as something real is heart of the problem with relativity and reverse causation. Once people catch on to the fact that they've been thinking about things all wrong all along, it'll settle down.

Time is just a concept humans came up with in order to help us live our lives. We found some fairly repetitive things in nature and used them as our basis... one rotation of the earth (day), one full moon cycle (month), one full orbit around the sun (year), etc. Now we know when to go to bed, when to plant seeds, etc. As we got a little more sophisticated, we broke the day down even further, and we could use it to schedule a busy day's activities, research and sequence the events leading up to a particular problem, etc.

We came up with this handy little device to tell us what time it was, sent it up in space, noticed it behaved differently at high speed, and the problems began.

Our concept of time references humans and our common experience. Once you take it outside of our experience and start doing cool interstellar things, it no longer applies.

In that, it's exactly like the rest of mathematics... it has absolutely no reality, because it's absolutely meaningless without context. It's just a set of rules that help us deal with the actual reality we experience. Once you start pushing at the edges of what humans can experience, the rules start to change.

Blatherskite, you seem to be talking about the measurement of time rather than time itself.

At the end, you say "Once you start pushing at the edges of what humans can experience, the rules start to change."

Can there be change without time? Are words like 'before' and 'after' meaningless? Can anything follow without time? Does everything really happen at once?

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Without proper context... yep. Before what? After what? They are concepts that describe relationships... same as math.

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From a certain perspective, possibly, yes. Remember that time is relative, and our experience of it is subjective. Sometimes an hour seems like a lifetime, and sometimes a lifetime is crammed into an hour.

The first thing to note about your latest posting, Blatherskite, is that it came *after* mine.

I have another question for you, but I think I'll wait for your response *before* I ask it...

Also, the question, "Can there be change without time?" has yet to be answered.

>>Sometimes an hour seems like a lifetime, and sometimes a lifetime is crammed into an hour.

Yeah, I've seen 24 too.

The main problem here (I think) is that RE and Blatherskite are talking about two different things. RE is talking about the *phenomenon* of time (time as we experience it), and Blathers about the possible structures of relationships in the "external world" which we represent as time.

Noggin

Treat time as one of many dimensions and it makes multi- dimensional mathematics simpler. Ignore time and assume infinite dimensions

Try to argue out of that it is like denying god whoever it is.

Isn't this a philosophical question rather than a scientific one? Is there ah PHex forum?

No, but there should be...

"Time is natures way of keeping everything from happening at once" -Graffito 19?? CE

"Time is natures way of keeping everything from happening at once" - was Albert Einstein.

turvy