# Can We Stop Time?

1. Apr 17, 2012

### shinnsohai

I'm not a student in this field , but still I'm having interest to know that.
When I was small, I used to play games and watch some sci-fic movies , which they can stop the time like "chronosphere" ?

Maybe we can stop the time at minor, just at the point of moving towards future or the past
If we let the "0" position as "Now"
Positive = Future
Negative = Past

but there's still question like... we'll be observing ourself ? or even change the history ?
Killing yourself in the past?

2. Apr 17, 2012

### ghwellsjr

There's a reason why they call them "games" and "sci-fic movies". You can stop them and even run them backwards but not in real life. Don't worry, you can't kill yourself in the past (and neither can anyone else).

3. Apr 17, 2012

### Naty1

You can't stop distance either!! Nor gravity....

None of them cooperate!!!!!

But eventually we might find a way to 'stop' gravity....via antigravity....
but not yet....stay tuned....

We can 'slow down time' by traveling at very high speed....for example, aboard a very high speed spaceship local time aboard passes at the normal rate,a traveler would age 'normally', but upon returning to earth such a high speed traveler could find that many years had passed....that his family, for example, had lived a 'normal' life and died long ago...

4. Apr 17, 2012

### Passionflower

If you stop time it is all over, according to general relativity time is stopped at a singularity.

5. Apr 25, 2012

### shinnsohai

It Seems that Time Travelling Is not Possible in real life !
But as you said that "Anti-Gravity"
I would like to judge it myself!!
but dint the bullet train apply the anti-gravity theory? it sounds float to me

6. Apr 25, 2012

### Ryan_m_b

Staff Emeritus
There is no scientific basis for antigravity. The bullet train is a maglev, the train is suspended due to a magnetic field. This is no more antigravity than the leg of a chair.

7. Apr 25, 2012

### jambaugh

Can we stop time?
Yes, just a moment >blink< I just did. Didn't you notice? Oh you were stopped and couldn't.

I'm kidding of course but consider what "stopping time" means observationally.

Seriously, time is a parameter we use to sequence events. You "stop time" when you stop paying attention to the sequence of events because time is an observer defined concept. Ceasing to observe is ceasing to observe.

Observation is fundamental to anything we say about the physical world so time is fundamental in this way. This may lead us to imagine time (and space) is something physically real which we can act upon. But it isn't quite. (Yes I know Einstein's theory says matter affects space-time but there's a subtlety there.)

Time and space are not objects but rather relationships between objects. Effects on the objects indirectly affect their relationship. In Einstein's theory we can model gravitational action on objects by expressing it in terms of the geometry of space and time. But space and time are still parametric mathematical objects in that theory. Parameters are how we enumerate and sequence events, and distinct from observables which we measure directly.

For example we don't measure an object's time, we check our clock to see "when" we measured an object's momentum or presence or mass. We may also check our coordinates to see where these things get measured. But a physical object does not carry around a set of t or x values. That is something we paint on the objects to sort them out.

8. Apr 25, 2012

### Khashishi

A black hole will stop time at the event horizon from the outside observer's point of view.

9. Apr 27, 2012

### RobGSpeed

This may get metaphysical...Wondering if there is an equation where you can 0 out time? would like to use it for a book. Will give credit if someone has a formula for 0 time handy.

Last edited by a moderator: Apr 27, 2012
10. Apr 27, 2012

### DrewD

yes, $t=0$. And yes, too metaphysical... glad I got my joke in before this is locked, usually I'm too late.

11. Apr 27, 2012

### shinnsohai

Geez!
This are going more interesting than i thought
Thanks Ryan_m_b for pointing out the "maglev"
Before you're saying about the maglev, i was wondering a hugh things that can be floated by human is considerate as anti-gravity.
well it seems , not really
magnetic levitation ≠ gravity levitation
:tongue:
For the "time" topic ,
If it is like what you've mention, time is a parameter that could't be stop
but in theory and equation we use it for calculation and so on.
In my college, the teacher who teach me mechanics do said that, every equation or theory is simply based on assumption

The curios part is , is we're calculate is simply on assumption instead of the precision value.
how can the "Creation of Human" can be so successful ?
Ex. NASA spacecraft , or other mega-structure

PS: I'm so glad that, there is a place like this to discover and discuss the unknown (Without being a scientist) Although is was a dream to be a scientist, but Im not really talented at all

12. Apr 27, 2012

### jambaugh

Well put! "Look Ma! My shoes work by anti-gravity!"

WRT Black holes "stopping time" at the event horizon. The observer's time certainly doesn't stop. And the time for an in-falling object goes on into the interior of the horizon. So where is time actually stopping? Again, time is parametric not an observable. We don't observe time we use it to sort sequences of events. It's our label on the events. This is what Einstein meant when he said "time is what a clock reads"... with the huge caveat of "which clock matters".

I may sound like I'm being pedantic but there is a real practical reason to make this distinction. Efforts to quantize gravity include some research into "quantum time" or "quantum space-time" and this is an error. Quantization is applied to observables (momentum for example, or spin) and not to parameters. Quantization of space-time (when we unify/relativize spatial coordinates too become parametric!) is as silly as quantizing ... say ... a group or a Lie algebra.

The other pragmatic aspect of making this distinction is exactly the purpose Einstein put to it. Understanding what is observer defined enables one to understand what is relative as distinct to what is physical. Time is relative...It just seems otherwise because we are all very small and very slow.

So you can stop a bus (brakes) and stop a clock (its a mechanical system) but stopping time is as meaningless as freezing angle, or fixing percentage.

13. Apr 27, 2012

### yuiop

We can take relative time as arbitrarily close to zero as we like, but maybe not exactly to zero. For example we could let an observer orbit just outside the photon sphere of a black hole and make each nano-second of that observers time equal to one billion years on the Earth. Achieving exactly zero relative time rate may be impossible, like achieving absolute zero temperature but we can get as close as we like. Achieving infinite time dilation (stopping the relative rate of a clock) using relative velocity requires that we have infinite energy which makes it impossible. Achieving infinte time dilation using gravitational time dilation, requires that we remain stationary at the event horizon which requires infinite force and infinite energy which again is considered impossible.

14. Apr 28, 2012

### jambaugh

One can make relative time completely zero. That isn't the point. In GR an observer's frame is a global system of clocks and measuring roads encoded as an arbitrary curvilinear coordinate system.

The distant external observer of a black hole is more like a specific coordinate system locally inertial to that observer. I can "tweak" the coordinate system in various ways, including considering the "natural" coordinates of a uniformly accelerating observer in the absence of any curvature. I get horizons and "stopping time".

The point is that it is improper (though poetic) to think of "time stopping". It is rather that the usual way we define coordinate systems gets "messy" and arbitrary when you consider curved space-time geometry and we can get coordinate singularities at the event horizon of a BH.

Note however that one place time really does stop is at the singularity of a black hole. There and at a hypothesized "Big Crunch" for the entire universe in some cosmological models would be the only places one could say time truly stops.

15. Apr 28, 2012

### sweet springs

Hello.

How do you define STOP TIME?

All the matter do not move? Even no motion requires the concept of time flow.

Regards.

16. Apr 28, 2012

### and9

Time is a dimension. It is a way of parametrizing what we physically observe. You have as good of a chance of "stopping" time as you do in "removing" or "stopping" a particular space coordinate from existence.

17. Jul 3, 2012

### HallsofIvy

Since your teacher is not here to defend himself, I suspect you misunderstood. One could argue that, if we do an experiment several thousand times and it always turns out the same way, it is only an "assumption" that if we did it again, it would turn out the same way. But if you were holding an antique vase, worth thousands of dollars above a concrete floor, would you "assume" that if you let go of it, it would fall?

I think you are misunderstanding what your teacher meant by "assumption".

18. Jul 24, 2012

### drbanner

Time only stops at the singularity.

19. Jul 24, 2012

### Naty1

But there IS evidence for repulsive gravity.....which is perhaps the term which would have been more recognizible. Alas, there is no theoretical basis for negative time...to stop observed time.