h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hi, I am from Germany. I hope I'll use the right words and you understand my English
Should that be a joke? "kill your grandfather in another universe" or something like that. do you believe in this things? no one has ever succeeded in trying something like that...like "time traveling".

hello researcher,
First; your English is fine, second; no that is not a joke. It all pretty much depends on how the physical laws of the Universe behave in respect to time.
The time-dimension is distinctly different from spatial ones in the sence that we seem only to be able to move in one direction. We don't find this the least bit strange as this is an integral part of our everyday life - time flows on and (alas) we get older. Nevertheless our instinct of what is true or false in large scale, high velocity, high mass or subparticle physics often is wrong. Understandibly because we have no ground to use our intuition on anything but what we grow up with.
Now, I can't say for you but I haven't really seen or travelled to other univeses. Therefor one shouldn't panic though the logic of such places don't always add up.
The multiple universes theory set forth to provide an explanation for the grandfather paradox states that there are not one but many "copies" of our universe. Imagine a universe as a stream where the depth and width of the stream are spatial dimensions (only two here as is common in spacetime illustrations) each cross section is then a universe at a given time (distance from the origin of the stream). Now, you are normally floating along, living your life in your cross section. Wether or not physically possible, you never swim up- or downstream and therefore never know what lurkes there.
Let's now say for the arguments sake that the physical laws of the stream allow swimming up or downstream. Then according to the multiple universe theory you will find a universe identical to the one you lived in. That is, the cross section that you swam to is identical to the one you came from. Then you will also find a copy of your grandfather which you can kill. As this is only a copy, and thus the grandfather to what would be a copy of you in the universe that you are currently visiting, the grandfather's death (althoug brutal) should have no consequence to your birth.
Of course this would totally shatter the future of the universe that you visit and create a disruption in the homogenousness of the universes. This disruption would still not progress up- nor downstream as one universe can't (?) affect other ones.
I hope this wasn't to complicated, but let me know what you think.
PS With regard to the questionmark above; No one can be shure of this. We haven't seen any effects caused by other universes (perhaps because no one is time travelling to them) but that doesn't mean that they either can't or won't. There even is a theory that states that gravitons (the bearers of the gravitational interaction (force)) can indeed travel between dimensions/universes. This theory could explain dark energy and the weakness of gravitation compared to the other three interactions (electromagnetic, weak and strong interactions)

hope this helped

Martin Swift

I wrote a paper discussing the theories you mentioned [Based on 'Unveiling the Edge of Time' (Gribbin) and 'About Time' (Davies) as well as others I do not recall.], back when I was in highschool, 7 years ago or so. Since then I have put a lot of thought into these ideas and there are two points I would like to raise.

1. We always make the assumption/statement that we have far more freedom in the three spatial dimensions than we do in the single dimension of time. The reason for this is because we always seem to be going 'forward' in time. However, we percieve being able to 'freely' travel in six distinct directions with regard to space. I would like to point out that our spacial 'freedom' is virtually insignificant.

True, I can catapult myself faster than the speed of sound by means of a ramjet or in earth orbit; but how do we quantify that in terms of 'free mobility'. Even when we move from one place to another, are we not being carried around the sun at tremendous speed and ever-shifting velocity just by virtue of being on earth? Even when we leave earth orbit are we not being carried along around our galaxy at an incomprehensible rate along with the rest of the solar system? Even if we were to leave our solar system would we not still be hurling through the universe just as all the rest of the matter in our galaxy is? Doesn't all that motion make whatever miniscule 'conscious' and 'decisive' motion we make essentially insignificant.

Can we truly stop our 'forward' motion through the universe? even actively moving towards another galaxy, can that motion overcome our current motion away from that galaxy, or even really halt it significantly? We know that at times we experience the passage of time more slowly than at others. (Such as being in slow-motion as one falls; as well as the alteration of time-perception that can be attained via meditation) One could argue that such 'percieved' time dilation is a pscyhological phenomenon, but perhaps it is 'freedom' of motion along the time dimension. (at least as much freedom as we actually have along the spatial dimentions.)

2. I had thought that even if time-travel were unattainable we should be able to transmit information faster than the speed of light, if not instantaneously. But my roommate this past year has a MS in Astrophysics from Princeton and is a doctor of Philosophy from Harvard, and he assured me that any real progress in such a direction implies also the potentiality of time travel. (based on the ideas of special relativity.) He also pointed out that the recent highly publicised 'breakings of the light barrier' could be explained in other ways and did not constitute a true ability to transmit information faster than light.

Though it does seem that regarding FTL information transmission, the little that I know about Quantum Mechanics (QM) promises that such an achievement is not completely impossible. Which would seem to say that Time Travel would be possible as well (Or there is some faulty assumption in Relativity?). [The only Time Travel QM theory that I'm aware of is the fairly hokey one used in Timescape by Michael Crichton.]

[uhh maybe i should have put this in an entry? it's huge.. i don't know what the conversation protocol is yet. I'm new.]

I suggest to you and others the reading (horrible experience though that may be for the layman, and even for the experienced in this field an arduous effort) of Weinberg's Gravitation and Cosmology, where all these matters are explained.
in short to your points:

1

All motion is relative. There is no such thing as "standing still" in our galaxy, only something as standing still relative to such and so an object. There is NO absolute speed in this galaxy, except for the speed of massless particles, such as photons. The changing of the perceiving of time I would indeed contribute to a psychological effect, because if you indeed altered the flow of time (be it on your persona, or just in a very small area around you) should create a measurable effect in how you are perceived by your surroundings.

2

As far as physical knowledge goes, there is no possibility of transmitting information at greater speed than the speed of light. With your reference to Q.M. you probably have the transportation (or Beam Me Up)-experiment. Though this experiment did succeed in transportation of information from one point to the other, without existing physically in the space between the two points, which was off course a major discovery, in fact the speed of information transfer wass still limited by the speed of light, because a "decryption key" had to be sent by regular means, in order for the information to make sense.

I have to think further about your response to my point #1 ..
i still think there's a simple way to express equal relative freedom in the time dimension as that which we have in the spatial dimensions...

of course i've been known to delude myself before.. so this would not be the first time

yitz..

In fact there is a simple way to describe this freedom: add more time-dimensions. This is an alternate description of the multiple universe theory, where you don't live on a one-dimensional time-arrow, but on a multi-dimensional path through multiple possibilities.
A restriction probably will be that the length of the arrow allways increases thanks to things as entropy. The zero point for both space and time should be the big-bang.

This is a fasinating topic...

Shooting one's Grandfather is harsh, to say the least.

Would I be able to give him a bunch of flowers and a box of chocolates instead?

If so do I buy them when I get there, or do I take some...
(which time travels best; dark, milk or white chocolate? I know, I'll take a selection...)

Seriously, though; I think time as an abstract artefact has it's own edges and definitions. Just like we can't easily measure ourselves walking on the ceiling, we can't measure ourselves folding time. This doesn't that the folding of time isn't possible - just that it can't be measured easily from within a strict scientific paradigm.

Ooooh, what about people that you see on a day-to-day basis?

And what about time-travelling back to meet yourself some years younger?

This is a fasinating topic...

Shooting one's Grandfather is harsh, to say the least.

Would I be able to give him a bunch of flowers and a box of chocolates instead?

If so do I buy them when I get there, or do I take some...
(which time travels best; dark, milk or white chocolate?)

I think time as an abstract artefact has it's own edges and definitions. Just like we can't easily measure ourselves walking on the ceiling, we can't measure ourselves folding time. This doesn't mean that the folding of time isn't possible - just that it can't be measured easily from within a strict scientific paradigm.

Ooooh, what about people that you see on a day-to-day basis?

And what about time-travelling back to meet yourself some years younger?

Even more interesting:
dating your mother and discovering later that you are your own father.

Difficult to top that one...

What about befriending yourself, having a massive row and then running yourself over with a car in a fit of rage.

Or standing at the top of Angel Falls, jumping off and time travelling mid flight to see yourself falling to your doom. A sort of temporal bungee jump.

And remember kids:

*** DON'T TRY ANY OF THESE STUNTS AT HOME ***

at least without the supervision of a grown-up.

My last post was written in haste, for there is a even much better story. I can't remember what it was called (something like 'All your zombies'), and who wrote it (I suspect Robert Heinlein, but I am not sure). The gist of it is:
A little baby-girl is brought to an orphanage. Twenty years later she is seduced by a guy that disappears after that night. Of course she becomes pregnant. During delivery in the hospital of a little girl she is found to be completely mixed up internally, and to save her life, she is transformed into a man. During that time, her/his baby is stolen.
Some years later, he is recruited by a time-traveling agency. After some assignments, he is ordered back in time, and to seduce a girl. Next morning his boss turns up, takes him along to nine month later and there gives him a justborn baby girl. This must be delivered to an orphanage some twenty years before...

also a bit like red dwarf where lister fertilises the invitro tube given to him by kochanski from the alternate dimension...takes it back in time and ends up being his own dad, and kochanski is his girlfriend and his mum.

time is indeed a tricky thing. the problem starts in measuring it. it doesn't have dimension, it doesn't have amplitude in fact the only thing we can really say about time is that it has progression. if you have ever done any relitivistic physics you will know that our concept of time is shattered as soon as we leave the earth. to measure time we use periodic processes like a pendulum or the decay of an atom. but what happens to a pendulum in zero gravity, and the atom will not decay at absolute zero. as you can see time is a very elusive entity and will always remain so. just as in quantum mechanics our knowledge of time is limited by heisenberg's uncertainty principle - the fundamental limit of knowledge, beyond which chaos reigns! (drama!)

I believe that we will eventually learn how to manipulate time, but I believe its origin and true nature will remain as mysterious as existance.

I'm involved with a thread on wave-particle duality:

http://www.bbc.co.uk/h2g2/guide/A156449

Maybe by shrinking someone to a size where wave-particle duality becomes viable, time-travel may become more probable.

According to wave-particle duality concepts a particle can exhibit wave-like properties and vice-versa. So for instance some physisists have joked that an electron, for example, is a particle Mondays, Wednesdays and Fridays and is a wave on Tuesdays, Thursdays and Saturdays (Sundays alternate).

The groovy thing about waves is that they exhibit some non-specific properties. Time travellers may be able to harness these wave-like properties to maybe not so much travel but more "surf" time.

So how could this be done?

By increasing the wavelength of your body or by decreasing the size of your body.

Is this possible? What would happen to someone's wavelength if they were shrunk by whatever means? How would you increase someone's wavelength.

All these questions and more answered in next weeks exciting episode...

I'm involved with a thread on wave-particle duality:

http://www.bbc.co.uk/h2g2/guide/A156449

Maybe by inducing wave-particle duality, time-travel may become more probable.

According to wave-particle duality concepts, a particle can exhibit wave-like properties and vice-versa. So for instance some physisists have joked that an electron, for example, is a particle Mondays, Wednesdays and Fridays and is a wave on Tuesdays, Thursdays and Saturdays (Sundays alternate).

The groovy thing about waves is that they exhibit some non-specific properties. Time travellers may be able to harness these wave-like properties to travel, fold or surf time (whatever word takes your fancy).

So how could this be done?

Probably by increasing the wavelength of your body or by decreasing the size of your body.

Is this possible? What would happen to someone's wavelength if they were shrunk by whatever means? How would you increase someone's wavelength.

All these questions and more answered in next weeks exciting episode...

I'm involved with a thread on wave-particle duality:

http://www.bbc.co.uk/h2g2/guide/A156449

Maybe by inducing wave-particle duality, time-travel may become more probable.

According to wave-particle duality concepts, a particle can exhibit wave-like properties and vice-versa. So for instance some physisists have joked that an electron, for example, is a particle Mondays, Wednesdays and Fridays and is a wave on Tuesdays, Thursdays and Saturdays (Sundays alternate).

The groovy thing about waves is that they exhibit some non-specific properties. Time travellers may be able to harness these wave-like properties to travel, fold or surf time (whatever word takes your fancy).

So how could this be done?

Probably by increasing the wavelength of your body or by decreasing the size of your body.

Is this possible? What would happen to someone's wavelength if they were shrunk by whatever means? How would you increase someone's wavelength.

All these questions and more answered in next weeks exciting episode...

Great, I've put the same thread on 3 times on and can't get them off.

Do I look stupid or what?

Maybe your message went timetravelling on its own, and passed the guide a few times.

I never thought of that

It is 'All You Zombies--', and it is by Heinlein. The story actually starts with the oldest version waiting to recruit the second oldest version. I also remember that the recruiter hates the song 'I'm My Own Grandpa.'

Just a fleeting idea but...

If someone was to time travel wouldn't that muck up (the already pretty shakey) theory of conservation of energy.

Travelling back in time consists of taking a packet of energy (a person to laymans like me). Wouldn't this result in an increase in energy in the place that you were travelling to and a decrease in the energy at the point that you left. Therefore leaving the universe in a deficit at the place you left.

Ok so i know this idea is a little confused but perhaps someone can help me shed some light on this idea?