# The Naked Scientists Forum

### Author Topic: Can time STOP under certain conditions ?  (Read 1792 times)

#### percepts

• Full Member
• Posts: 53
##### Can time STOP under certain conditions ?
« on: 01/08/2014 01:28:57 »
In a recent topic it was said (in effect) that the further you are from the center of gravity, the faster time is. Therefore it follows (I think) that the closer you are to a center of gravity, the slower time is.
So that begs the question, is there a condition where time can stop and how would it appear to us? Would we cease to be concious? i.e cease to be able to think?

#### PmbPhy

• Neilep Level Member
• Posts: 2760
• Thanked: 38 times
##### Re: Can time STOP under certain conditions ?
« Reply #1 on: 01/08/2014 02:26:33 »
Quote from: percepts
In a recent topic it was said (in effect) that the further you are from the center of gravity, the faster time is.
The rate at which time flows is always referred to a particular clock. If you have a clock that is in a gravitational field, say near the sun, then the further out another clock is the faster it will run but only up to a limit. When the clock is so far away that the potential energy is near zero then clocks further out will run at the same time (ignoring infinitesimals).

Quote from: percepts
Therefore it follows (I think) that the closer you are to a center of gravity, the slower time is.
So that begs the question, is there a condition where time can stop and how would it appear to us?
The only thing I can think of is a clock at rest at the event horizon of a black hole. A clock sitting there would not tick as observed by clocks outside the black hole. There are two conceptual problems with this. First off its not possible for observers outside the black hole to observe the clock not ticking. Second the clock cannot be at rest at the event horizon as observed by observers sitting next to the clock.

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3758
• Thanked: 46 times
• The graviton sucks
##### Re: Can time STOP under certain conditions ?
« Reply #2 on: 01/08/2014 02:41:51 »
There is an issue with the concept of time as you view it. Time is the yardstick by which we measure rates of change. However, rates of change are affected by gravity and acceleration. Therefore we postulate time dilation. Einstein showed that even at absolute zero we still have zero point energy so nothing ever stops. If it ever did stop completely then we would be in a situation that there would be no available energy to start the next change. This would be equivalent to there being no mass-energy present at all. This raises an interesting question. What is it that gives mass-energy its existence? From the previous remarks it would appear that one important element is constant motion. So looked at this way it would appear that the answer to your question is no, time can never stop completely.

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3758
• Thanked: 46 times
• The graviton sucks
##### Re: Can time STOP under certain conditions ?
« Reply #3 on: 01/08/2014 02:53:04 »
Quote from: percepts
In a recent topic it was said (in effect) that the further you are from the center of gravity, the faster time is.
The rate at which time flows is always referred to a particular clock. If you have a clock that is in a gravitational field, say near the sun, then the further out another clock is the faster it will run but only up to a limit. When the clock is so far away that the potential energy is near zero then clocks further out will run at the same time (ignoring infinitesimals).

Quote from: percepts
Therefore it follows (I think) that the closer you are to a center of gravity, the slower time is.
So that begs the question, is there a condition where time can stop and how would it appear to us?
The only thing I can think of is a clock at rest at the event horizon of a black hole. A clock sitting there would not tick as observed by clocks outside the black hole. There are two conceptual problems with this. First off its not possible for observers outside the black hole to observe the clock not ticking. Second the clock cannot be at rest at the event horizon as observed by observers sitting next to the clock.

I keep asking myself questions about the situation at the event horizon. Particularly about the observer at that point. They can't be experiencing nothing. It might be slowed down but as in the spirit of the OP's question, can it stop completely? I think not.
« Last Edit: 01/08/2014 02:56:48 by jeffreyH »

#### evan_au

• Neilep Level Member
• Posts: 3934
• Thanked: 225 times
##### Re: Can time STOP under certain conditions ?
« Reply #4 on: 01/08/2014 12:44:42 »
Quote
I keep asking myself questions about the situation at the event horizon. Particularly about the observer at that point.
With stellar-mass black holes, a human would be torn apart by tidal forces before they reached the event horizon - "spaghettified".

However, if you had a galactic-mass black hole, the tidal forces at the event horizon are small enough for a human to survive. In this case, a human observer could in theory reach the event horizon - although from their point of view, the journey would be over in an instant, since the intense gravity would cause them to approach the black hole at a significant fraction of the speed of light.

A recent hypothesis suggests that there is a "firewall" at the event horizon of a black hole, such that an observer passing into the black hole would pass through a region of intense radiation from their point of view and timescale (observers far from the black hole would see only extremely red-shifted Hawking radiation, equivalent to a very low temperature).

Now if only I could find a black hole and some marshmallows...

See: http://en.wikipedia.org/wiki/Firewall_(physics)#Characteristics

#### The Naked Scientists Forum

##### Re: Can time STOP under certain conditions ?
« Reply #4 on: 01/08/2014 12:44:42 »