What is time?

I’ve always wanted to know if time exists and what it is.
Is time just a human invention made for remembering events? if not than what is it? how, when, why, you know, the usual questions.
I’m looking for the answer about this for quite a time now, so i hope you can help me with this mates.


What sort of thing would count as an answer to you? For example, if I asked “What is space?”[sup]*[/sup], what kind of answer might you give?

*: The sense of “space” I am asking about is the one which is to “time” as “spatial” is to “temporal”, of course; not, like, “What is outer space?” or “What is this wide key on the bottom of my keyboard?”

I don’t think anybody really knows the answer to the question, but this article by Lee Smolin, goes some way towards answering the question and also tries to debunk the notion that time is an illusion and does not really exist.

Isn’t it fair to say that time is a ratio of disance and rate?

How would you define rate without time?

How could it be anything other than “made up”? Its certainly not a noun, I can’t go out and get a bucket of time. You can measure the passage of it but only by using units we also made up. Our measurement of it is based on real things, such as the rotation of our planet, but just like our base 10 numbering system, it didn’t have to be. If we didn’t hold it in such high regard, we would never be late for appointments.

Time is what stops everything happening all together. :slight_smile:

Give this book a try:

Travels in Four Dimenions: The Enigmas of Space and Time (also available in paperback)

It’s an accessible, well-written discussion of the difficulties in defining time (and space).

Time is a manmade construct for the purpose of measuring events, just as the inch is a manmade construct for the purpose of measuring length.

Time does not really exist, therefore time-travel is not possible. However, there is a phenomenon that gives the impression of time travel. As one approaches the speed of light, velocity has the effect of slowing one’s impression of time, but what is known as “time” does not really slow. Time is relevant.

For example, suppose an astronaut boarded a vehicle capable of a high-speed low orbit which could be observed here on earth. Here, we could observe the vehicle orbit the earth 5 times a second. This experiment continued for twenty-years. When the astronaut finally came back to earth, we would find that he/she had only aged 1 year.

From the astronaut’s perspective, he would perceive that he had only been in orbit for 1 year, but came back to earth 20 years later, thus the impression of time-travel.

Time did not really slow down, the astronaut’s perception of time was altered due to the physical effects of velocity.

I believe this is incorrect. When I sleep, my perception of time is radically altered, but I still age however many hours I’m sleeping. If an astronaut were accelerated out at 0.999999c and back (without turning into a strawberry-colored jam at the ends of the spaceship), she would actually not have aged as much as someone hanging out on the planet. The half-life of any radioactive elements on the spaceship would extend relative to the same elements staying on the planet.

I don’t think it’s perception – the actual passage of time, whatever that is, is altered.

The same can be said of a lot of things. Temperature, color, distance.

All of these are ways of measuring and describing our world.

“Time” is very much a noun. Being a noun isn’t a semantic property; it’s a syntactic property. “Time” can serve as the subject of a clause and so on, which is all it takes. This is the problem with teaching lexical classes with slogans like “A noun is a person, place, or thing [or idea, or whatever]”.

Not getting how there is no “time”. Seems to me there are a number of ways to deal with it:

  • The thermodynamic arrow of time
  • The cosmological arrow of time
  • The radiative arrow of time
  • The causal arrow of time
  • The particle physics (weak) arrow of time
  • The quantum arrow of time
  • The psychological/perceptual arrow of time

See: http://en.wikipedia.org/wiki/Arrow_of_time for descriptions of the above.

No, seconds are a manmade construct for measuring time, as inches are a manmade construct for measuring distance.

Time travel is possible, in one direction.

Time exists as much as distance.

On the contrary, you can’t NOT get a bucket full of time.

Time is a component of spacetime, which is as real as anything else. It’s a physical thing that we measure; not something we made up.

Time is the progression of movement of objects in relation to one another. That’s about it.

I don’t understand why people agonize over this or why it’s even really considered a question. The above answer satisfies me completely. It seems like people want time to be something other than what it is, to understand it as an object or something.

If time is a human invention then how did time pass before humans came along? The universe had a good 13 billion years of time before people stepped in and declared that they invented it. It’s like saying humans invented the Earth because we measure meters and inches along the surface of it.

Dinosaur’s still exist man! The Earth is only 6000 years old, of course it is, how could it not be? 6000 years ago was when man invented time! Now shut up stop questioning me, I’ll have none of this blather about what happened, BEFORE time. :smiley:

Time exists in the same way the electromagnetic spectrum exists - humans have just tried to impose arbitrary divisions onto it.

I’ve always wondered how time works with something like a photon.

Imagine you were a photon (conscious and all that). At the speed of light time stops. To you the whole universe is flat…you can get from one end to the other in zero time. Yet to someone else it takes you eons (and then some) to do that. Indeed you will never make it from one side to the other…but then from your perspective you do.

Just thinking out loud.