M & String

@lemon-lime said
A paradox is a scenario that doesn't work, and time travel is an idea that lends itself to paradoxes.

The grandfather paradox is a familiar one. If you go back in time and kill your grandfather before he has children, there will be no future you who could go back in time. You wouldn't exist because your father or mother didn't exist, but this is impossible because you were the one who caused your own non-existence.

Here's another paradox.
It involves a time machine, and to a lesser degree a mad scientist with a secret agenda.

In the wee hours of the morning a time machine from the future materialises in the living room of an MIT grad, who has been up all night pondering the mysteries of life... i.e. he doesn't have a girlfriend.
The time machine opens revealing a traveler from the future. The time traveler explains the operating principles of time travel to the startled MIT grad, and then leaves him and the machine to go off and follow his true passion in life. He wants to remain in our time and live as a cabbage farmer on a bunny wabbit ranch.

So Derrick (the MIT grad) examines the machine, keeping in mind the operating principles of time travel, and in short time is able to built other working models. Knowledge of what he has done goes public, and Derrick is heralded as the inventor of time travel.
But he didn't invent the time machine, he simply built other working models of a time machine from the future.
And so here is the paradox... who invented the first time machine?

meanwhile, back at the ranch...

The time traveler from the future has settled into his new life as a cabbage farmer/bunny rancher. He gave up time travel to pursue his true passion in life... genetic engineering. And only time will tell if he succeeds in creating a new race of highly intelligent predatory man eating bunny rabbits.

@lemon-lime said
Here's another paradox.
It involves a time machine, and to a lesser degree a mad scientist with a secret agenda.

In the wee hours of the morning a time machine from the future materialises in the living room of an MIT grad, who has been up all night pondering the mysteries of life... i.e. he doesn't have a girlfriend.
The time machine opens revealing a traveler from t ...[text shortened]... tell if he succeeds in creating a new race of highly intelligent predatory man eating bunny rabbits.

That's a nice retelling of the "who wrote Johnnie B. Goode?" paradox from Back to the Future.

If you haven't seen it, Michael J. Fox goes back in time and plays/sings the song 'Johnnie B. Goode' at his own mom's high school prom. Marvin Berry (Chuck Berry's brother) was listening and called up Chuck to announce that he had found that new sound was looking for. He held up the phone to the speaker so Chuck could hear the song being played that he had not even written yet.

@lemon-lime said
Here's another paradox.
It involves a time machine, and to a lesser degree a mad scientist with a secret agenda.

In the wee hours of the morning a time machine from the future materialises in the living room of an MIT grad, who has been up all night pondering the mysteries of life... i.e. he doesn't have a girlfriend.
The time machine opens revealing a traveler from t ...[text shortened]... tell if he succeeds in creating a new race of highly intelligent predatory man eating bunny rabbits.

Exxxxxcept ....... all those paradoxes vanish if an entire new universe pops into existence every time a timeline is altered.

However, I still stand by my theory that time travel is far more unlikely than FTL hyperspace travel.

@bunnyknight said
Exxxxxcept ....... all those paradoxes vanish if an entire new universe pops into existence every time a timeline is altered.

However, I still stand by my theory that time travel is far more unlikely than FTL hyperspace travel.

Entire new universes popping into existence seems like a heavy price to pay for avoiding anomalies and paradoxes. Where is all of that extra mass and energy supposed to come from?
It's much easier for me to imagine a timeline as a long line of falling dominos, with cause and effect always moving in one (and only one) direction. Time travel (especially into the past) is fun to think about, but I can't imagine it actually happening. Once a domino falls it can't (all by itself) un-fall.

FTL hyperspace travel sounds like a shortcut, where you don't necessarily need to travel faster than light to get somewhere before a beam of light traveling through normal space gets there.
Is that about right?

@lemon-lime said
Entire new universes popping into existence seems like a heavy price to pay for avoiding anomalies and paradoxes. Where is all of that extra mass and energy supposed to come from?
It's much easier for me to imagine a timeline as a long line of falling dominos, with cause and effect always moving in one (and only one) direction. Time travel (especially into the past) is fu ...[text shortened]... et somewhere before a beam of light traveling through normal space gets there.
Is that about right?

If one universe can exist, why not more than one? Spacetime continuums don't exist within, or inside, any kind of larger "container," so there's no question there would be "room." Every universe is a closed system, in theory -- unless the latest physical theorizing has gone way off the deep-end since I last took a look at it.

@wildgrass said
That's a nice retelling of the "who wrote Johnnie B. Goode?" paradox from Back to the Future.

If you haven't seen it, Michael J. Fox goes back in time and plays/sings the song 'Johnnie B. Goode' at his own mom's high school prom. Marvin Berry (Chuck Berry's brother) was listening and called up Chuck to announce that he had found that new sound was looking for. He held up ...[text shortened]... the phone to the speaker so Chuck could hear the song being played that he had not even written yet.

Yeah, I remember that scene.
If Chuck Berry hadn't heard Marty McFly play/sing that song then Marty wouldn't have heard Chuck singing/playing it later on so that Marty could hear it before going back in time to perform it so that Chuck...

It seems the only logical answer to "who wrote Johnnie B. Goode?" is... no one.
The song is self existent.

@soothfast said
If one universe can exist, why not more than one? Spacetime continuums don't exist within, or inside, any kind of larger "container," so there's no question there would be "room." Every universe is a closed system, in theory -- unless the latest physical theorizing has gone way off the deep-end since I last took a look at it.

There seem to be more and more theories that are essentially unprovable. Fun to think about, and possibly useful for filling in gaps and patching up inconsistencies (such as gravity being a relatively weak force), but at the end of the day unprovable.

Unprovable theories never go away, they just pile up in a corner somewhere and collect dust.
And the next thing you know, you've got quantum dust mites to deal with... ugh, nasty little critters.

@lemon-lime said
Entire new universes popping into existence seems like a heavy price to pay for avoiding anomalies and paradoxes. Where is all of that extra mass and energy supposed to come from?
It's much easier for me to imagine a timeline as a long line of falling dominos, with cause and effect always moving in one (and only one) direction. Time travel (especially into the past) is fu ...[text shortened]... et somewhere before a beam of light traveling through normal space gets there.
Is that about right?

Indeed hyperspace travel is supposed to be a shortcut -- it bypasses normal space. Of course my big question is what would be the passage of time in that shortcut relative to time in normal space.

A far as universes go, the whole concept of the very existence of "stuff" is so weird-n-strange that I wouldn't assume anything at this point.

@lemon-lime said
There seem to be more and more theories that are essentially unprovable. Fun to think about, and possibly useful for filling in gaps and patching up inconsistencies (such as gravity being a relatively weak force), but at the end of the day unprovable.

Unprovable theories never go away, they just pile up in a corner somewhere and collect dust.
And the next thing you know, you've got quantum dust mites to deal with... ugh, nasty little critters.

Theoretical physics trades almost exclusively in mathematics. In the past this approach, which I believe hinges largely on notions of symmetry, has proven highly predictive. But lately, yes, it seems that the theoreticians are spinning theories that have no hope of being experimentally tested any time in the near future, if ever. Still, experimentalists sometimes can concoct clever ways of testing a hypothesis that no one foresaw.

Too much emphasis, by which I mean grant money, is put on string theory. Competing theories are, I guess, just not sexy enough to fund, but so far string theory has been nothing but a 10^500-card deck of jokers with no good playing prospects.

@bunnyknight said
Indeed hyperspace travel is supposed to be a shortcut -- it bypasses normal space. Of course my big question is what would be the passage of time in that shortcut relative to time in normal space.

A far as universes go, the whole concept of the very existence of "stuff" is so weird-n-strange that I wouldn't assume anything at this point.

The way I see it, so-called hyperspace travel is just a concept of travel without laboring under the tyranny of the Intermediate Value Theorem. To wit: is there a way to alter one's spatial coordinates from (x_1,y_1,z_1) to (x_2,y_2,z_2) without passing through any points of space between them?

And all time travel is, really, is the same question, but with the time coordinate tacked on. One problem with time-traveling is, even if it were possible, one would still need to control one's spatial coordinates too. Traveling from spacetime coordinates (x_1,y_1,z_1,t_1) to (x_1,y_1,z_1,t_2) will likely end with the time traveler dying in the vacuum of space upon arriving at time t_2.

@soothfast said
The way I see it, so-called hyperspace travel is just a concept of travel without laboring under the tyranny of the Intermediate Value Theorem. To wit: is there a way to alter one's spatial coordinates from (x_1,y_1,z_1) to (x_2,y_2,z_2) without passing through any points of space between them?

And all time travel is, really, is the same question, but with the time c ...[text shortened]... ,t_2) will likely end with the time traveler dying in the vacuum of space upon arriving at time t_2.

Recently I've heard of theories that normal-space could theoretically be compressed, or even folded, but if that also causes time to be compresses or frozen, then you'd return from your trip and find your friends much older or long dead.

And I most certainly wouldn't dare to hyper-travel or time-travel without an armored space-suit as a bare minimum.

@bunnyknight said

And I most certainly wouldn't dare to hyper-travel or time-travel without an armored space-suit as a bare minimum.

I'm wearing Tommie Bahamas & Khaki shorts

@ogb said
I'm wearing Tommie Bahamas & Khaki shorts

Please do not ... I repeat, DO NOT hyper-travel wearing that outfit. Don't say I didn't warn you.

@lemon-lime
The funny part about time travel is this: You would need to solve the hyperspace speed problem, FTL for any long deep time trips because the Earth is in a corkscrew path around our galaxy, one major circle every 200 million years give or take.
So if you want to go back to see the Chicxulub asteroid hit 66 million years ago, Earth is going to be about 1/3 the way round the circle or so, say 120 degrees of the circle for example, so if you wanted to visit that time frame you would have to move in space some 30 to 50,000 light years to meet up with Earth of that past.
So you have to have both FTL AND time travel, otherwise you would find yourself basically in deep space and in 60 million years the whole galaxy would not be in the same place so you would most likely be in deep space between galaxies wondering who turned the lights off...…

Besides all that, you would have to be able to predict exactly where Earth was 66 million years ago so there would be a significant navigational issue also.

Good luck seeing the dinosaurs...….

@sonhouse said
@lemon-lime
The funny part about time travel is this: You would need to solve the hyperspace speed problem, FTL for any long deep time trips because the Earth is in a corkscrew path around our galaxy, one major circle every 200 million years give or take.
So if you want to go back to see the Chicxulub asteroid hit 66 million years ago, Earth is going to be about 1/3 the w ...[text shortened]... ago so there would be a significant navigational issue also.

Good luck seeing the dinosaurs...….

Methinks that FTL travel would be child's play for anyone capable of time travel, while their navigation computer would easily handle destinations with pin-point accuracy. However, getting a battery to power all this is another matter.