What's your favourite paradox?

A favorite of mine came from a movie "Bedazzled" The Devil says to the main character. "Listen carefully. I'm lying. ---- You know that I'm lying because everything I say is a lie."
 
Brian Rogers said:
The time travel paradox is solved if we assume the multiple dimensions theory. If one can only travel on a single branch of time, anything you do in the past simply generates a new dimension, not affecting the future of that particular branch of time. But then if you could travel forward in time, then could you ever get back to your original timeline? What would happen if you met yourself in the future or...if you ran into your wife in the future and she turns out to be your daughter or granddaughter (depending how far into the future you went). This isn't really a paradox but I find it unreasonably fascinating...
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There is also the non-paradox view of time travel.
If you go back in time you will always have had gone back in time and the present is dependent upon you having done that. By definition you've already done whatever it is that you actually do once you get there, regardless of your well laid plans.

Any fantasy of killing some historic figure, or whatever, will simply prove to be fruitless. Of course, records that we are all relying on to know what happened at a prior time are incomplete so maybe you'll simply learn more about actual events of the time rather than changing them.

I have in my brain memories of books and short stories that follow this model, though I can't think of any at the moment.
 
Everything in moderation. - Must include moderation. You mustn't be immoderate with your moderation.
 
The Gulliver's Travels Paradox. Or the struldbrugg paradox.

To be immortal but continue to mentally decline and have your language lost to time and understanding.
 
Hi,

If we're going for time travel paradoxes, they can all be resolved by the simple expedient of assuming the concept of eternalism - which essentiall says that the past is as real as the present. It actually exists like the pages of a book you're reading that you've read. So you can go back a few pages and rewrite the text with a marker pen. It doesn't change anything further along. Of course if you assume a universe like this you've already done away with cause and effect.

Consider a billiard ball rolling along a table, hitting another ball and transferring its momentum / kinetic energy to the second ball which rolls on while the first one stops. All very simple really. But under eternalism, the past exists, which means that the first ball can't have transferred its kinetic energy to the second still it's still somewhere out there with all its kinetic energy intact. Further, there's no reason that one instant in time should be in any way related to the one after it. (Unless you assume a designer of course!) After all why does one page of a book follow logically from the previous?

So consider the actual history of time under eternalism.

Instant one - a billiard ball rolls along a table.
Instant two -the universe is swallowed by a black hole
Instant three - two giant space whales are playing tennis
Etc.

Fun isn't it!
 
Time travel #1
Assuming insertion and retrieval are a product of technology in the ‘present’, then physical time travel creates a branch at the point of insertion. The traveler can experience life in the branch, but any changes to known history (from his/her perspective) don’t exist when they return to their present+time in the past. So, useful for historical research (and spying) but otherwise just recreational (and morally self-indulgent).

Time travel #2
Physical time travel is impossible but energy patterns in the past can be manipulated, including memories (would require knowledge of a person’s exact location at a precise time). The one season ‘Odyssey 5’ goes down this route. The ‘sending’ technology is somehow shielded from chronometric backlash, and must remain so, isolated from the new timeline, as a concealed anomaly.
 
Time is an illusion, created by humans to make sense of the time between things happening.

Something happens, which causes something else to happen; the bit in between is what we call 'time'. What is done can be undone, but it's impossible to go back and not do the original thing in the first place.

As what we see is merely light, and we only see it when light from the 'happening' hits our eyes, it is possible to see things that happened a long time ago, such as a star that went supernova millions of years ago only being seen now because it's taken that long for the light to travel to Earth.

It is conceivable (although improbable) that with powerful enough visual equipment, and the ability to either travel faster than light or be transported from point A. to point B faster than light can get there (perhaps through a wormhole) that we could witness events on Earth that happened hundreds, thousands and millions of years ago. It's theoretically possible. But actually interaction with things that have already happened isn't.
 
What would happen if an immovable object met and irresistible force ? An inconceivable smash .:D

Im not sure , but I think this is one Zeno's Paradoxes . What it boils down to is , you can have one or the other but, not both at the same time. :)
 
If you apply strict logic to reality you're bound to run into a lot of paradoxes... does that mean that logic is full of paradoxes, or reality is?

I was reminded of one that I like yesterday: every time you remember an event you change it slightly. This means that the purest memories you have are those you forgot immediately and never thought of again.
 
paranoid marvin said:
Time is an illusion, created by humans to make sense of the time between things happenin
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Time is the perception of change in physical things that themselves exist only in the present. The past doesn't exist nor does the future. Only the instant of the present does. But in that instant there is an ongoing alteration in the state of things that physically exist and since we have memories of previous states we become aware of the alteration as "time". Hence time travel to the past is impossible. Any being that is not subject to alteration is by definition outside of time. So God is outside of time, hence he doesn't have a beginning or end. He just exists.
 
Another one is the Fermi Paradox, but it's easily solved. Aliens (presuming for the sake of argument they exist) haven't contacted us or reached us because they can't. Even the most powerful signal is lost against background Cosmic radiation after only a few light years, and since the laws of physics and chemistry apply everywhere in the universe, it is virtually impossible for any living organism to survive the aeons required to travel even to nearby stars, never mind stars halfway across a galaxy. And why would they come here? There's no way they can know we exist.
 
Justin Swanton said:
Time is the perception of change in physical things that themselves exist only in the present. The past doesn't exist nor does the future. Only the instant of the present does. But in that instant there is an ongoing alteration in the state of things that physically exist and since we have memories of previous states we become aware of the alteration as "time". Hence time travel to the past is impossible. Any being that is not subject to alteration is by definition outside of time. So God is outside of time, hence he doesn't have a beginning or end. He just exists.
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I did special relativity at uni and it's such an interesting way of looking at the world I keep in practice - there were all sorts of nooks of it I never quite 100% got. In SR there's no absolute here-and-now : Any position in space and time can potentially be a here-and-now for someone - but none of them are 'the' now, and someone else can legitimately have you somewhere other than your 'here' and the moment you've defined as 'now'. And what you see from each one depends on how you and your surroundings are moving relative to each other. The only way to get a consistent picture is to throw out an absolute here-and-now entirely and just go with everyone having their own sense of time and place. But the really head messing thing is that if you do that you can get a consistent picture, that works pretty well as a model of things within it's limits. Which kind of suggests that there really isn't a set here and now - there's just a universe where nothing is fixed, and as many different points of view on it as there are viewers.

Bear in mind: I'm not pushing this as the ultimate truth, but for the situations it was designed to deal with (things moving at high speed with constant direction and speed) it does work very well. To me that does suggest that even our most fundamental concepts for understanding the world are just approximations we come up with to get by.
 
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StilLearning said:
I did special relativity at uni and it's such an interesting way of looking at the world I keep in practice - there were all sorts of nooks of it I never quite 100% got. In SR there's no absolute here-and-now : Any position in space and time can potentially be a here-and-now for someone - but none of them are 'the' now, and someone else can legitimately have you somewhere other than your 'here' and the moment you've defined as 'now'. And what you see from each one depends on how you and your surroundings are moving relative to each other. The only way to get a consistent picture is to throw out an absolute here-and-now entirely and just go with everyone having their own sense of time and place. But the really head messing thing is that if you do that you can get a consistent picture, that works pretty well as a model of things within it's limits. Which kind of suggests that there really isn't a set here and now - there's just a universe where nothing is fixed, and as many different points of view on it as there are viewers.

Bear in mind: I'm not pushing this as the ultimate truth, but for the situations it was designed to deal with (things moving at high speed with constant direction and speed) it does work very well. To me that does suggest that even our most fundamental concepts for understanding the world are just approximations we come up with to get by.
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My understanding of relativity is that change in an object slows down the faster it goes, hence the perception of time in a subject will also slow down if he travels a good deal faster than a more stationary subject. But both subjects remain in the same instant of the present. There aren't two presents (Santa is tightfisted).

I don't quite get the point about "here". Different objects are naturally in different locations. Two objects can't occupy the same space.
 
Justin Swanton said:
My understanding of relativity is that change in an object slows down the faster it goes, hence the perception of time in a subject will also slow down if he travels a good deal faster than a more stationary subject. But both subjects remain in the same instant of the present. There aren't two presents (Santa is tightfisted).

I don't quite get the point about "here". Different objects are naturally in different locations. Two objects can't occupy the same space.
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Palms up, this is a very artificial situation I'm about to describe, but it's tailored to illustrate the point without making the example unreadably long and full of caveats. I'll preface it by pointing out that, in it's most basic form, special relativity only deals with non-accelerating frames of reference. You can 'hack' it (lots of folks would take issue with that term, but it's always struck me as apt) to deal with accelerations, but this is something that general relativity does more explicitly and comprehensively.

We have Al and Bert, two astronauts (they could equally be a hydrogen molecule and a galaxy, they just represent two reference frames) who are in a part of space where they've no measurable reference points but each other. They're moving - coasting - relative to each other with some significant speed. Special relativity's big postulates (which sounds like a euphemism for a boil to me, but I digress) are that everyone has to measure the speed of light as the same (but there's no strict single value for any other measurement) and everyone measures distance and time, from their own positions, the same way (i.e. the laws of physics are the same in each reference frame). Al and Bert both have a clock, a torch and a tape measure of some sort to measure things with.
With no reference point except each other, neither one knows if Al is still and Bert moving, Bert still and Al moving, or both moving with some fraction of their total relative velocity. Since they are coasting, so they feel no forces and stay at constant speed relative to each other, all three scenarios actually appear exactly the same to both of them. Because they have to both see the speed of light as the same value, they both see the other astronaut's measurements of time and distance being slow and short, by the same amount. Since turning around, and meeting up to compare, would introduce an acceleration they can't do so to see whose clock is actually faster, without leaving the situation our bare-bines special relativity deals with.
If they disagree on whose clock is faster they're going to get two different measurements for each other's speeds, or the speed of any 3rd object we introduce. So they don't agree how long it's been between two events happening, and so they don't agree on where they were relative to each other when they happened.
If we now introduce a third astronaut, Una: She disagrees with both Al and Bert about whose clock is fastest, and about where everyone was at any given time. If we have a given sequence of events - Al flashes his headlights, Una lights a cigar, Bert sneezes - they all see the timing and position of each event differently, and you can easily create scenarios where they even see them in different orders. So everyone has a different take on where they are at any given time, what the time is from any given person's viewpoint, and what order things are happening in.

To be fair: As the entity magically setting up this artificial scenario we're free to just say 'this is how it is' and set the positions, speeds, and times of each astronaut at any given moment. But that only works if we stay outside the scenario, and use 'creator's privilege' to just dictate those measurements. If we have to use light, measuring sticks, and clocks to find out the measurements, the way our astronauts do, and if they can see and measure us the same way, we become just like them and we just have another viewpoint they can disagree with.
 
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It is possible, even likely, that I've made mistakes of either explanation or of understanding in my above post. However, as long as I've gotten the main points right I hope it gives some flavour of the weirdnesses.
 
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