Is time linear?

I do future time travel every day.

Kind of makes you respect me, doesn't it?

This will absolutely crack you up. I posted my blurb and gazed out the window for a moment to think about what I had just said. I furiously went into edit mode to change my meaning* (I am sure you knew my intended meaning), only to discover the future has been altered by you!

* building a device to go faster into the future (of course if we have a vehicle that can do a reasonable % of C we can travel faster into the future with a machine, relative to those that stay behind).

Is time travel possible? Here is a fab audio from Dr. Marc of NASA that automatically loads and plays.

Neo will like this:

What is time? Is time travel possible? For centuries, these questions have intrigued mystics, philosophers, and scientists. Much of ancient Greek philosophy was concerned with understanding the concept of eternity, and the subject of time is central to all the world's religions and cultures. Can the flow of time be stopped? Certainly some mystics thought so. Angelus Silesius, a sixth-century philosopher and poet, thought the flow of time could be suspended by mental powers:

Time is of your own making;
its clock ticks in your head.
The moment you stop thought
time too stops dead.

The line between science and mysticism sometimes grows thin. Today physicists would agree that time is one of the strangest properties of our universe. In fact, there is a story circulating among scientists of an immigrant to America who has lost his watch. He walks up to a man on a New York street and asks, "Please, Sir, what is time?" The scientist replies, "I'm sorry, you'll have to ask a philosopher. I'm just a physicist."

Most cultures have a grammar with past and future tenses, and also demarcations like seconds and minutes, and yesterday and tomorrow. Yet we cannot say exactly what time is. Although the study of time became scientific during the time of Galileo and Newton, a comprehensive explanation was given only in this century by Einstein, who declared, in effect, time is simply what a clock reads. The clock can be the rotation of a planet, sand falling in an hourglass, a heartbeat, or vibrations of a cesium atom. A typical grandfather clock follows the simple Newtonian law that states that the velocity of a body not subject to external forces remains constant. This means that clock hands travel equal distances in equal times. While this kind of clock is useful for everyday life, modern science finds that time can be warped in various ways, like clay in the hands of a cosmic sculptor.

Science-fiction authors have had various uses for time machines, including dinosaur hunting, tourism, visits to one's ancestors, and animal collecting. Ever since the time of H.G. Wells' famous novel The Time Machine (1895), people have grown increasingly intrigued by the idea of traveling through time. (I was lucky enough to have chats with H.G. Wells' grandson, who told me that his grandfather's book has never been out of print, which is rare for a book a century old.) In the book, the protagonist uses a "black and polished brass" time machine to gain mechanical control over time as well as return to the present to bring back his story and assess the consequences of the present on the future. Wells was a graduate of the Imperial College of Science and Technology, and scientific language permeates his discussions. Many believe Wells' book to be the first story about a time machine, but seven years before 22-year-old Wells wrote the first version of The Time Machine, Edward Page Mitchell, an editor of the New York Sun, published "The Clock That Went Backward."

One of the earliest methods for fictional time travel didn't involve a machine; the main character in Washington Irving's "Rip van Winkle" (1819) simply fell asleep for decades. King Arthur's daughter Gweneth slept for 500 years under Merlin's spell. Ancient legends of time distortion are, in fact, quite common. One of the most poetic descriptions of time travel occurs in a popular medieval legend describing a monk entranced for a minute by the song of a magical bird. When the bird stops singing, the monk discovers that several hundred years have passed. Another example is the Moslem legend of Muhammad carried by a mare into heaven. After a long visit, the prophet returns to Earth just in time to catch a jar of water the horse had kicked over before starting its ascent.

Time travel is possible. Today, we know that time travel need not be confined to myths, science fiction, Hollywood movies, or even speculation by theoretical physicists. Time travel is possible. For example, an object traveling at high speeds ages more slowly than a stationary object. This means that if you were to travel into outer space and return, moving close to light speed, you could travel thousands of years into the Earth's future.

Newton's most important contribution to science was his mathematical definition of how motion changes with time. He showed that the force causing apples to fall is the same force that drives planetary motions and produces tides. However, Newton was puzzled by the fact that gravity seemed to operate instantaneously at a distance. He admitted he could only describe it without understanding how it worked. Not until Einstein's general theory of relativity was gravity changed from a "force" to the movement of matter along the shortest space in a curved spacetime. The Sun bends spacetime, and spacetime tells planets how to move. For Newton, both space and time were absolute. Space was a fixed, infinite, unmoving metric against which absolute motions could be measured. Newton also believed the universe was pervaded by a single absolute time that could be symbolized by an imaginary clock off somewhere in space. Einstein changed all this with his relativity theories, and once wrote, "Newton, forgive me."

Albert Einstein, whose theories of relativity changed our understanding of time and space, once wrote "Newton, forgive me." Einstein's first major contribution to the study of time occurred when he revolutionized physics with his "special theory of relativity" by showing how time changes with motion. Today, scientists do not see problems of time or motion as "absolute" with a single correct answer. Because time is relative to the speed one is traveling at, there can never be a clock at the center of the universe to which everyone can set their watches. Your entire life is the blink of an eye to an alien traveling close to the speed of light. Today, Newtonian mechanics have become a special case within Einstein's theory of relativity. Einstein's relativity will eventually become a subset of a new science more comprehensive in its description of the fabric of our universe. (The word "relativity" derives from the fact that the appearance of the world depends on our state of motion; it is "relative.")

We are a moment in astronomic time, a transient guest of the Earth. Our wet, wrinkled brains do not allow us to comprehend many mysteries of time and space. Our brains evolved to make us run from saber-toothed cats on the American savanna, to hunt deer, and to efficiently scavenge from the kills of large carnivores. Despite our mental limitations, we have come remarkably far. We have managed to pull back the cosmic curtains a crack to let in the light. Questions raised by physicists, from Newton to Kurt Gödel to Einstein to Stephen Hawking, are among the most profound we can ask.

Is time real? Does it flow in one direction only? Does it have a beginning or an end? What is eternity? None of these questions can be answered to scientists' satisfaction. Yet the mere asking of these questions stretches our minds, and the continual search for answers provides useful insights along the way.

http://www.pbs.org/wgbh/nova/time/through.html

You're right. I didn't think the question through. I suppose I could have asked "is time constant?" Or "is time constant to a stationary observer?", knowing that a stationary observer is not possible.

What I am really getting at is, comparing time to a stream, is it possible to
slow the stream? (apparently, yes),
stop the stream?
walk downstream?
walk upstream?

Thanks ebrown_p and Chumly for your interesting input. I'll be back Monday

I once read many years ago that we go back in time when we cross the international dateline. That the astronauts that orbit the earth gain or lose time for each revolution. I'm not sure how they calculate such time. It's beyond my math skills.

There is no stream, Neo (forgive the Matrix reference, I couldn't resist).

But a "stream" turns out to be a terrible metaphor for time. The best way to explain this is to give a couple of examples.

Through these examples keep in mind the primary axiom of Relativity-- "Every perspective is equally valid". Actually let me clarify this.... a "perspective" in this sense is what one "observer" will measure. This may be different than what another observer measures... but in this case neither is more correct than the other.

First, in every example you can think of... you will always experience time as normal. You will always see a watch you are wearing (provided it is not broken) go the same speed. You will always experience one second each second. This is because in your perspective time is time and you will observe it going the same rate it always does.

That's easy and obvious.

The difficult part is that someone else may observe the same time differently (although from their perspective they will experience time the same rate). It turns out two ways to change your perspective (the scientific term is "Frame of Reference") are either your speed relative to the other... and a gravitational field.

I like ebrown_p!

Imagine you are in a spaceship and I see you moving at near the speed of light. Of course in my frame of reference, I am not moving (and you are moving). In each of our spaceships is a light that we see fire once every second.

I will look at my light and see it fire once every second. I will look at your light and see it fire at less than once per second. This is the paradox... I see the time in your spaceship going slower than it is going in my spaceship.

You, of course will see things differently. You may very well know that it is YOUR spaceship that is stationary and it is my spaceship that is moving. You (of course) will see YOUR lamp blinking once every second (and you can check this with your watch which (unfortunately) is also in your spaceship.

You will then look at my spaceship and see that from your perspective, my light is blinking at less than once per second.

So we have two different perspectives. We observe things in two different ways. And we even observe the time between two event (i.e. my light blinking twice) as diffferent amounts of time.

The key is that it is impossible for anyone to say whose point of view is correct-- in fact they are equally correct. They are just measured from two differen Frames of Reference.

i just saw your post...that part of the brain is called the suprachiasmatic nucleus...your welcome

before i can answer, i need to say im 14, and just a little... lets say bored with the high school curriculum.

Now, time can only be linear if it really exists. In the human mind, time can only go as broad as past, present, future.
But what are these?

Past is just a way of placing things that happened before the present in a place to describe where/when it happened. Future is a way of explaining what is yet to come. But what is present?

based on the above, present is just future moving into the past, but for that to happen, the past would need to be future. This cannot be, therefore some lucky bugger decided to add the present, witch is just a way to place the transition.

So, in a way of explaining if the future is the present, then if we look a year in advance, what did we just look into?

A year in advance.

Look at the statement. looking at a future event that in the illusion of time will come and pass us, moving into the past. skip a head and the year is here aaaaand.... ZOOM! gone.

The future is now the past. It barely said hello! And look! what what was the future is now the past, one and the same.if the past is the future gone by, then it is still the future.

There for the past does not exist, hence the present or the future cease to exist. that year went by. Before it passed, it was in the what-would-be-but-isn't future, witch means i did not exist then. not if your disregarding this, let me say this- time may not exist, but we(humanity) have made a way of linking people together with unprecedented precision, go lets just role with it!

plus, for the sanity of everyone, lets n0t change anything. we've all been trough enough **** for that.

It was some decades ago that I read about objective time changes that humans experience when we travel by air. I remember reading about the time change, but don't remember what those time changes were.

Sir, do I have permission to borrow this statement for a discussion I am having?

Heliotrope has not posted in over 4 years...

Good grief!

Look at the time. . .

Thrown for a curve again for not observing timestamp, eh?

time is a concept created by humans in the beleif that things happen in a linear fashion this is incorrect time does not happen linear because time does not truely exsist yes you can go into the past but that really is just a different dimension of one place. its this that makes time travel not real infact its not time travel at all instead it is traveling through dimensions therefore all wormholes that go through time actually go through dimensions. ways to see this would be if you tried to open a wormhole one minute in the past and shoot yourself it may actually happen but it may not affect you because it would then be a different dimension. henceforth no time is not linear at all. if it was then "fate" would be real one example is "seeing into the future" that future may actually happen or it may not its just more likely to happen. nothing is set in stone therefore time does not actually go linear and it does not actually exsist.

It varies on factors outside the universe as we know it.

Though within the universe time tapers... always and forever, sometime parallel to material aging and sometimes polar to it, though time being merely an observable variable, this appears to mean more than it does... Psychological grasp of the motion of time amounts to little more than a novelty, actual real world alterations in temporal shift, alter only the subject, not the entirety of the area around such a thing.

Reversing temporal fields amount to measurable factors across other dimensional qualities. Again, as with zero point, we can see it, protect against it, but not truly insert a probe to accurately produce usable results, only intriguing results.

We can use time without pondering that issue in all ways, we will in fact do so, though no real endeavor to toy with it will be needed.

Unless usable results to you are to reach your own grasp that this is true and have a few novel tools for localised alteration faster. Though it begs the question why send extremes, IE: a bomb or some fruit, forward in time?.. The field will be affected by altered environmental factors too... That we have too much fruit today and not enough tomorrow is best fixed using resources wisely, not emitting vasts amount of energy to achieve the same result.

To localise temporal alteration the other direction alters everything, even in the facility, unless off world.... Temporal linearity of harvesting is flawed unless some other you dies because of it in another dimension. And that is simply non-viable in any terms applied as paradox occurs, paradox at %>0 error margin in one form or another which would not be realised, thus some form of decay would occur, if universal linearity of physics is standard, the decay margin variances set in taper as they are, allowed for in equations.

Forever we expend vast amounts of effort in placing tomorrows harvest from area one in area two's box, when errors we cannot account for need only be patiently averted, with patience and planning..

To step into temporal sciences use of time itself, we would have to prove our worth to alien races who fear their destruction. In my opinion, for little more than a novelty of expedience, in a universe where eternal survival already exists.