Reply to: Cheap Time travel

[mudskipper]

Time doesn't really matter but our perception of it does. If you want to live forever just watch party political broadcasts over and over again.

Wasn't there a character in Catch 22 who subscribed to a similar philosophy?

[SpontaneousOrder]

Ok supposing the man isn't on a mountain but flew in a fast jet Eastward (this is important I understand)? Would he experience time as slower to the man on the ground??

East or west doesn't matter.
Both would experience time as normal. But both would observe the other as 'passing through time' more slowly so long as both remain observing from an inertial frame of reference.

If the jet did a u-turn and cam back then it would have spent the time taken to do the u-turn in a non-inertial frame, and as such the scenario falls outside the scope of 'special' relativity. In this case the jet pilot would see the other guy aging more slowly, and then as he performed the u-turn he'd see the other guy rapidly age so that he is now aged more than the pilot. Then during the return trip he's see the other guy age slowly again - but not enough to fully counter that period of rapid ageing. When the pilot gets back to the start both men will agree that the jet pilot has aged less than the stationary man.

[gingerjedi]

Well even ignoring gravity, the clue was in your own posting. You kept saying 'relative to each other', but a man at the foot of a mountain and a man at the top are not moving at all, relative to each other.

They're only moving relative to each other if you choose some arbitrary 3rd party frame of reference. So ignoring gravity there would be no time dilation at all.

Ok supposing the man isn't on a mountain but flew in a fast jet Eastward (this is important I understand)? Would he experience time as slower to the man on the ground??

[SpontaneousOrder]

I bow down to your superior knowledge, I must admit my understanding of the subject comes from the layman's version of 'A Brief History of Time' (The Universe in a Nutshell) and 'Planet of the Apes'.

I must have skipped the bit about gravitational time dilation.

Well even ignoring gravity, the clue was in your own posting. You kept saying 'relative to each other', but a man at the foot of a mountain and a man at the top are not moving at all, relative to each other.

They're only moving relative to each other if you choose some arbitrary 3rd party frame of reference. So ignoring gravity there would be no time dilation at all.

[gingerjedi]

No. They aren't moving relative to each other, so there is no relative velocity time dilation - only gravitational time dilation. Gravitational time dilation doesn't mirror both ways because it falls outside of special relativity (and into general relativity).

In this case the man on the mountain would age more.


I believe Scoots comment, though, is related to you using the word 'travel' - time is a dimension and so it doesn't travel. Infact the word travel by definition implies a change in position in relation to a change in time; so that's a limitation in the english language - it's very hard to talk abut time in a non-recursive way.

I bow down to your superior knowledge, I must admit my understanding of the subject comes from the layman's version of 'A Brief History of Time' (The Universe in a Nutshell) and 'Planet of the Apes'.

I must have skipped the bit about gravitational time dilation.

[scooterscot]

Someone at sea level would conclude that time has passed more slowly for the man on the mountain.

Someone with very sharp eyesight.

[SpontaneousOrder]

Someone at sea level would conclude that time has passed more slowly for the man on the mountain.

No. They aren't moving relative to each other, so there is no relative velocity time dilation - only gravitational time dilation. Gravitational time dilation doesn't mirror both ways because it falls outside of special relativity (and into general relativity).

In this case the man on the mountain would age more.


I believe Scoots comment, though, is related to you using the word 'travel' - time is a dimension and so it doesn't travel. Infact the word travel by definition implies a change in position in relation to a change in time; so that's a limitation in the english language - it's very hard to talk abut time in a non-recursive way.

[gingerjedi]

You did say it:

But the man on the mountain lives longer relative to the man on the ocean floor, I did also say I should have clarified that it is relative to the observer.

Someone at sea level would conclude that time has passed more slowly for the man on the mountain.

[scooterscot]

You did say it:

He did right enough.

Top gun science rules of engagement exist for your safety and for that of your team, they are not flexible nor am I. You either obey them or your history Mr, is that understood?

[scooterscot]

Thankyou d000hg

The OP starts off with a scenario where he introduces the idea that an almost inconceivably small time delay equates to time travel and then has the cheek to debunk my valid point (admittedly equally inconceivable), I should have clarified that it is relative to the observer.

Double standards.

Not my workings but here you go:

Gravitational time dilation - Wikipedia, the free encyclopedia

Oh calm down, don't get your panties in a twist.

[SpontaneousOrder]

Thankyou d000hg

The OP starts off with a scenario where he introduces the idea that an almost inconceivably small time delay equates to time travel and then has the cheek to debunk my valid point (admittedly equally inconceivable), I should have clarified that it is relative to the observer.

Double standards.

Not my workings but here you go:

Gravitational time dilation - Wikipedia, the free encyclopedia

You did say it:

That's wrong isn't it? I thought time travelled slower at altitude?

[SpontaneousOrder]

He didn't say it did.

No but (relative) movement does. If you sit on the bottom of the ocean or on a hill, you are moving at a different speed.

You've got that wrong.

If you're at the bottom of a hill then you are moving slower (Relatively speaking) - so you experience more time passing, not less.

You are, however, in a region of less gravitational potential which means that time will pass slower in that respect.

I don't know which will outweigh the other, and it would depend on how deep down you are and how dense the particular planet you're on is (i.e on a very large, but not very dense planet then the speed difference could be large while the gravitational potential difference is very small.).

[SpontaneousOrder]

I would like to say there's no such thing as 'now'.

It's quite difficult to remove this idea from your head once it's made a home. But as others have pointed out my 'now' will be moving at a different rate from your 'now'. There's no such thing as a universal 'now'.

Holding onto that thought, everybody's personal 'now', it's become possible that I could see into your past.

More worryingly it suggests that free will is an illusion. Regardless of how our 'nows' are played out our destination is the same.

Time for a coffee.

'Free will' doesn't even make sense. Why on earth would you want non-deterministic 'free will'? If it's non-deterministic then it's random, and where is the value in random decision making?

[gingerjedi]

I can't remember, do GPS satellites need relativity adjustments? If so is that predominantly due to reduced gravity or greater velocity relative to us on Earth?

Yes, they 'tick' faster as gravity is weaker.

I admit I did have to look it up.

http://physicscentral.com/explore/writers/will.cfm

Also, the orbiting clocks are 20,000 km above the Earth, and experience gravity that is four times weaker than that on the ground. Einstein's general relativity theory says that gravity curves space and time, resulting in a tendency for the orbiting clocks to tick slightly faster, by about 45 microseconds per day. The net result is that time on a GPS satellite clock advances faster than a clock on the ground by about 38 microseconds per day.

[d000hg]

I can't remember, do GPS satellites need relativity adjustments? If so is that predominantly due to reduced gravity or greater velocity relative to us on Earth?