eple

If we believe in time as a line, then we cannot believe in eterinty. We will ask: "when did it all begin?". Eternity has no beginning and no end. If the universe is eternal, we cannot fully understand it.

If we believe in space, we do not believe in eternity either, we will ask: "where does it all end?", then end up with "what is beyond the end?".

Thus, both time and space are illutions created because the human brain cannot grasp the consept of eternity.

Any views on this?

CSflim

Well, I wouldn't go so far as to say that time and space are an illusion, but the truth about them is certainly quite counter-intuitive.

Time does not "flow" unstoppable, like a river. There is no absolute time. We cannot say that two spatially separated events A and B happen at "the same time", as such a thing doesn't exist.

The classic example of this is the Twin Paradox, which is not really a paradox, unless you believe that there exists a "universal time", which is the same for everybody.
(The twin paradox: Two identical twins. One goes onto a space ship, and blasts off at near light speed around the galaxy. He returns some time later. As far as he is concerned, he has been away from earth for a year. His body has aged a year, and all of the clocks onboard, confirm this fact. However, at home his twin has aged by fifty years, and all of earth's clocks confirm that fifty years have passed. A paradox? Two clocks correctly given different times? No, not unless you believe in "universal time")

Further more, time doesn't extend backwards to "minus infinity". Time extends backwards, only as far as t=0. Before this time, there was no time.
Some people fail to see how you could have a moment in time, before which, there was not previous moment, but as an analogy, consider a journey to the north pole. When you finally get to the north pole, can you keep going north?

As for whether time is infinite in the forward direction, we have yet to determine. It is possible that time is finite, and the universe will end in a "big crunch", but at the moment, it seems that the evidence points away from this possibility, and towards the opposite, a total heat death, where time never ends, but the universe just keeps getting bigger and bigger, and colder and colder, and less dense and less dense.

As to whether space is finite or infinite, you have to realise that you cannot separate the two. Speaking of time independent of space, or of space independent of time, is precisely meaningless. Space and time are just manifestations of a unified "space-time". As such, if time is finite, so is space, if time is infinite so is space.

Further more, the true nature of "space", may not be directly as we appear to intuitively grasp it (it the same way that time is also counter-intuitive). I'm sure that you have heard before that "space-time is curved". The only way to easily explain what that means, is to use the classic example of a curved earth's surface.
If you look at the ground, it appears flat to you. You conclude that the surface of the world is a flat two-dimensional plane. Seems to make sense!
Until you realise, that the earth is actually round, and that the two-dimensional surface, is actually curved around, and so the ends meet each other.

Similarly with space. We see space as being "obviously" three dimensional and "flat", but in reality, the "three-dimensional" space-time is also curved in a similar manner to the curved two dimensional plane of the earths surface.

The question is, is it "positive" curvature, or "negative" curvature. In other words, is it curved in on itself, to create a closed "sphere" of sorts, or is it curved away from itself, to create a "saddle" shape?
This question is actually equivalent to the question "is space infinite?", which is equivalent to the question "is time infinite?" (See what I mean about not being able to speak about one without including the other?)

If space-time is finite, then it must be closed, like a "sphere", but if space-time is infinite, then it is open, like a "saddle", (alternatively, it could be a very "flat" saddle, making it a flat plane, which is also infinite).

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TIO

CSfilm, the thing that has always bothered me about the twins paradox is not that the stationary one gets older. I've done enough physics to see that, and I'm quite comfortable with time dilation.
The thing is, it seems to assume that the Earth is an inertial FoR. I don't see why the twin in the spaceship doesn't see the earth accelerate away from him, then fly around a bit and come back. From his FoR, shouldn't the Earth twin be 49 years younger?

For a more intuitive scenario (in that it doesn't appeal to our intuition that the Earth is an inertial FoR), what if the twins were both in rockets, and they both flew away from each other and back? What if one flew off and the other didn't?

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Strewth

CSflim

Velocity is relative, acceleration isn't.

If we look at a spaceship with a constant velocity moving across the sky, we can say either:
a)The spaceship is moving relative to the earth
or
b)The earth is moving relative to the spaceship.

Both are correct. As far as people on the earth are concerned, they are static.
As far as the people on the spaceship are concerned, THEY are static.
If you carry out any experiment on board the moving spaceship, you will get precisely the same results, had yo performed it on board the "stationary earth".

However, accelearation is quite a different thing to constant velocity.
Acceleration requires a FORCE. Constant velocity does not. There is no force of motion acting on the spaceship, nor is there a force of motion acting on the earth(^1).

If you are now to imagine a spaceship accelerating across the sky, you cannot make the claim that the spaceship is stationary, and it is the earth that is accelerating. The force of motion is acting on the spaceship.
This can be objectively proven. If you carry out experiemtns on board the accelerating spaceship, you will get different results to what you would have expecting to get assuming the spaceship was stationary.

A simple analogy can be made as so:
When you are on a train, which is moving smoothly and constantly, you don't feel anything strange. You can get up, and walk around as normal. Walking towards the front of the train, feels the same as walking to the back of the train. Exactly as you would expect given a stationary train.
Now imagine that the train decelerates very rapidly (i.e. brakes) if you are not in your seat, you will be thrown off your feet! Not what you expect to happen while on an umoving train!

Hope that helps you to understand the difference between acceleration and constant velocity, and presumably, you can now apply it to your knowledge of time dialation, to fully understand the twin "paradox".

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1: Not strictly true, there is a centripedal force acting on the earth (Gravity of the sun), which causes an angular acceleration. But the earth remains at a constant linear velocity, which is what matters in this argument.

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twotimesadingo

it's these kinds of discussions that make me want to study physics with greater fervor.

but alas, i can't get through those damned introductory courses.

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I'll be the one to protect you from your enemies and all your demons.
I'll be the one to protect you from a will to survive and voice of reason.
I'll be the one to protect you from your enemies and your choices, son.
They're one and the same I must isolate you, isolate and save you from yourself."
- A Perfect Circle

CSflim

Hey, just do what I do......read!

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anti fishstick

haha yeah. i need to read up on this stuff more..

but ah, i do not believe in time as a line..

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And the day came when the risk to remain tight in a bud was more painful than the risk it took to blossom.
~Anais Nin

CSflim

No belief is required. Time is not a line. The twin paradox is not some arcane mathematical hypothesis. It has been carrtried out an verified.
Admitedly, it was not human twins that were used, but rather atomic clocks, and they did not different by years, but rather nanoseconds. But ultimately that makes no difference. Two perfectly synchronised clocks, giving different results.

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anti fishstick

so they've proven time isn't a line thru this twin paradox? interesting. i'd like to know more

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And the day came when the risk to remain tight in a bud was more painful than the risk it took to blossom.
~Anais Nin

John Henry

Although I accept the physical theory behind the atomic clock experiment, I am uncomfortable with the fact that the measurements taken were on such a small scale. If the difference was only nanoseconds, assuming this is within acceptable error for atomic clocks and that the experiment was proven to be rigourously repeatable, how do we know that the difference could not be accounted for by other effects of the differences in environment of the two clocks

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"No one was behaving from very Buddhist motives. Then, thought Pigsy, he was hardly a Buddha, nor was he a monkey. Presently, he was a pig spirit changed into a little girl pretending to be a little boy to be offered to a water monster. It was all very simple to a pig spirit."

Rodney

What do I care? I'm hungry. I want my breakfast.

CSflim

First of all, two synchronised atomic clocks deviating by (say) 80 nanoseconds in the course of a few hours is a HUGE divergence given that they are usually accurate to one second in 20 million years.

Second of all, the theory doesn't predict that there will be "some" undefined divergence. It predicts very precise amount of divergence, and the these predicted results have been verified to be accurate to an extemely high level of precision. It would take one hell of a coincidence for a "random" deviation due to the effects of the environment to line up so perfectly with the predictions.

Thirdly, this experiment is not a once off thing. Relativity has been rigorously tested, and the theory has spectacularly held every time.

Fourth, relativity is a practical working theory, much the same as Newtonian mechanics. Relativistic effects have to be taken into account by NASA. Think about how GPS works. The satelites orbiting about the earth need to know precisely where they are. This requires their on board clocks to be precisely synchronised with earth time. The computers on board are programed to peridically readjust their clocks, to account for the relativistic divergence. (clocks on satelites are under a weaker gravitational field than those on the earth's surface).

Fifth, relativity also predicts other effects, than those to do with time. Most famously is the fact that we can see a star which should be obscured by the sun due to the bending of the light rays as predicted by general relativity.

links
Will an atomic clock on the International Space Station be slower than a synchronized atomic clock on the ground?

What is the experimental basis of Special Relativity?

Relativity Tutorial
This page looks good. I didn't read it, but it looks as though it will give a good solid, introduction to relativty, that it reasonably simple to understand.

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ForgottenKnight

Great explanation and links CSflim. Thanks for sharing the knowledge.

My thoughts as for the origional statements/questions: I view time as a concept created by man for man. And I view eternity as a concept created by man for man. So if man wants time to be a infinate line rather than an finite line segment and therefore cannot understand eternity, then it is that man's choice to not understand eternity.

Eternity is everything from the beginning to the end, no matter where the beginning or end are, or even if there is a beginning or an end. It could be just one big infinate loop. If that is the case, then after the end comes the beginning, and after the beginning, the end, and so on.

Time is how time is, and it is different for everyone.

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"People say I'm strange, does that make me a stranger?"

CSflim

I don't see the logic in claiming that time is a social construction, due to our inability to comprehend infinity.
Time can be either finite or infinite....it is still time regardless.
Second of all, if time is only something that you have created, then why can't you see into the "future"? (which doesn't exist remember).

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John Henry

Thanks for the info. If I werent so lazy I'd have looked it up.

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"No one was behaving from very Buddhist motives. Then, thought Pigsy, he was hardly a Buddha, nor was he a monkey. Presently, he was a pig spirit changed into a little girl pretending to be a little boy to be offered to a water monster. It was all very simple to a pig spirit."

dy156

I didn't know where to put this, and I apologize in advance if I seem to be hijacking a thread, but I found this, among all places on ESPN.com's Page 2 Tuesday Morning Quarterback, a very long and insightful look at the past week's NFL games, with some philosophy and educational stuff thrown in too. This astounded me, but I thought the people reading this could appreciate it or tell me that it is old news or something. Since we know so little about the universe, it is very possible that time and space are merely illusory.


"Last week at a University of Chicago conference, cosmologists mapped out plans to attempt to locate "dark matter" and "dark energy." I don't wish to alarm you, but at least 90 percent of the universe is missing. Astronomers hope to find it.



When cosmologists measure the gravitational attraction on heavenly bodies, at least two-thirds of the matter in the cosmos appears to be missing; stars move as if acted upon by more gravity than can be accounted for by observed amounts of normal matter. For years, this has led to speculation that there is "dark matter" or "missing mass" throughout the firmament -- perhaps as strange forms of subatomic particles not present in this solar system, perhaps as very heavy black holes, perhaps as huge numbers of almost-stars hard to see because they don't shine. There are other theories. Searching for the missing mass has for decades been an obsession of astrophysicists.



The Hubble Telescope can't find the missing universe? Hey, guys, try directing it away from the Eagles cheerleaders.


Then, a few years ago, astronomers made the unexpected discovery that not only are the galaxies rushing away from each other, they are speeding up. It had been assumed that the Big Bang provided the impetus for the movement of the galaxies; and across the eons, momentum from the Bang would wear off, causing the galaxies to slow down. Instead, they're speeding up: the evidence looks solid. Cosmic acceleration cannot be happening unless something unseen is pushing on the galaxies -- that is, adding energy to them. Hence, dark energy.


The new betting line among scientists is that the luminous, observable forms of energy in the universe -- shining stars, natural radio waves and X-rays and so on -- constitute only a small share of total energy. Some force much more potent, dark energy, carries most of the power in creation; dark energy has so much power that it's speeding up unfathomable numbers of galaxies across unfathomable distances. The existence of dark energy would answer the riddle of why gravity does not cause everything in creation to crush together: Dark energy is repelling the components of the universe at the same time that gravity attracts them. And it's looking like dark energy is stronger than gravity --stronger, perhaps, by orders of magnitude.


Here's the rub. While there are theories about what dark matter might be, no one has the slightest clue what dark energy is. No instrument can detect it. No one knows its source or how it works. Dark energy appears strong enough to push the entire universe, and yet science can't locate it.


Bear this in mind when you're tempted to think Homo sapiens already understands the physical world, or even has the slightest idea what's going on. Combining missing dark matter and missing dark energy, science can't locate 90 percent of the universe! Bear this in mind, as well, when you're tempted to think we "know" there is no nonmaterial realm. An energy strong enough to push the entire universe is pulsing through your body right now, yet science has no idea how it works or where it originates. How many other nonmaterial forces might there be?


As for the University of Chicago conference, hope you didn't miss this session: "APEX-SZ, a Millimeter-Wavelength Galaxy Cluster Survey Using the Sunyaev-Zel'dovich Effect.""

CSflim

dy156 that article missed out the ultimate irony!

Einstein postualted the existence of such a force, and called it the "Cosmological Constant".
Later on he revoled this, and claimed that this was "the biggest mistake of my life"!

The genius can't be wrong...even when he tries!

With regards to the last paragraph, I don't think any scientist would make the claim that he understands the physical world.
It is only public perception which builds the picture that science is "finished", and that the only things we don't know about are completely insignificant things like what happens when particle A smashes against particle B at a few hundred miles an hour.

Simple fact.
We have two excellent physical theories, General Relativity and Quantum Mechanics, each of which works brilliantly in its own field.
Here's the rub: They are completely and utterly incompatible.
Einstein spent the latter half of his life trying to bring them together under his "unified field theory", but failed.
Richard Feynmann made a notable attempt with his theory of Quantum Electrodynamics, but ultimatly failed.
All the top modern physicists (Hawking, Penrose, etc) have tried, and are still trying to this day.

EDIT: The unification of Quantum Mechanics and General Relativity is what people are talking about when they refer to a Theory of Everything or a Grand Unified Theory.

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