# What is time?

1. Oct 8, 2011

### elosin

What is time??

2. Oct 8, 2011

### Staff: Mentor

It is the thing referred to by the "t" in many physics formulas.

3. Oct 8, 2011

4. Oct 8, 2011

5. Oct 8, 2011

### juanrga

An evolution parameter.

6. Oct 8, 2011

### Joel_GMG

Time is a value we use to chronicle changes in matter.

7. Oct 9, 2011

### Phrak

It's the same stuff as space, but different.

8. Oct 9, 2011

### N468989

Time is the rate at which things change. Some perceive it as fast others slow. It is said that if we were capable of travelling at the speed of light time would stop.

9. Oct 9, 2011

### Phrak

So you think time has a relative velocity. Care to clarify this-- you know, as the ratio of one thing compared to another. What are you comparing?

10. Oct 9, 2011

### med17k

time is another dimension of space in which all particles in the universe move in one direction only .but because all particles around us move in time with approximately the same velocity we find it hard to visualize time as a dimension of our universe.

11. Oct 9, 2011

### N468989

The time as we perceive is relative to the observer. The biological time is constant, which is the rate at which we live. If we where to go outer space and travel at speed near the speed of light we would age less compared to people on earth, thus "travelling into the future". When we came back everyone would of aged much more.

Gravity also influences time, it is well known that due to the gravity force or field that satelites "time" is slower than earth time. That is why the GPS (Global Positioning System) time has to be adjusted.

12. Oct 9, 2011

### elosin

Whao, all of this are new information. thanks they help alot=D
But one more question, if time is (space ,other dimensions that things travel to one direction.), What is before time? If time is what is mention, anything that happen before that should not even happen. Hence if that did not happen how does time even start?

13. Oct 9, 2011

### N468989

Nobody knows, if anyone states anything it is only a theory. In my opinion we will never know, but we will eventually get closer...

I believe everything has always existed, we are just newcomers to this reality.

14. Oct 9, 2011

### Staff: Mentor

The question is nonsensical. Time defines before and after, so it doesn't make sense to ask what is before time. That is like asking "what is north of lattitude".

15. Oct 10, 2011

### N468989

I think that what he means is what happened before the big bang which is our time reference (13.7 billion years ago).

16. Oct 10, 2011

### Phrak

You didn't get my point. Time, as you use the word, is not a rate, nor is there something like a "biological time constant" that measures elasped time.

Anyway, sure: elapsed time differs for different observers.

17. Oct 10, 2011

### cbd1

Time is separation in space-like points in spacetime. The more separation the space-like points (i.e. the less dense the spacetime), the faster the relative rate of time. (This is seen with gravitational time dilation.) If there is no separation between space-like points--like at a singularity of a black hole--time does not pass.

Thus, before the Big Bang came out of singularity, there was no separation in space-like points, so time was not passing.

Only if there was an event preceding the big bang, in which there was separation (i.e. a contracting cycle, or 'big crunch') time didn't ever pass prior to the instant the big bang came out of singularity.

18. Oct 10, 2011

### Staff: Mentor

To our current understanding that is like asking "what is north of the north pole."

19. Oct 10, 2011

### nitsuj

Easy, south pole.

Maybe the question "what was before time?" implied a frame of reference different from the one without time. i.e. looking at a black hole from Earth. (your statement regarding north of north pole implies same thing, otherwise south pole is right)

Last edited: Oct 10, 2011
20. Oct 10, 2011

### Staff: Mentor

In what way is the south pole north of the north pole? The south pole is, by definition, not north of anything.

21. Oct 10, 2011

### nitsuj

When the Earth is upside down. (the perspective of the observer standing on Earth facing the south pole)

22. Oct 10, 2011

### elosin

What I meant is, if you don't even have a time yet or time has not been created. How can you have a before and after if you do not even have a time line? Time is what we human define but is does it even really exist something call time?

23. Oct 10, 2011

### Staff: Mentor

Exactly. That is why the question is nonsensical.

24. Oct 10, 2011

### Staff: Mentor

Nonsense. The location of the poles has nothing to do with the perspective of any observer. Similarly, at any location on the globe, which direction is north and which is south is unrelated to the perspective of any observer.

25. Oct 10, 2011

### nitsuj

Cardinal directions have to be coordinated with something, that's always implied and is intuitive. Because you didn't explicitly mention what the cardinal directions were coordinated with I specifically assumed it was with the observer. So a north direction from the north pole is heading towards the south pole.

Saying you can't travel in a north direction when at the north pole is nonsensical.

Saying you can't travel a "north pole" direction when at the north pole is true but a singularity that seems much different than one for time.