You couldn't use a time machine to visit the 13th century

    After a day of pondering it struck me - the concept is still very valid and to be dealt with, however there is a way to get around that. We can predict the locations of the earth in regard to the sun and relatively nearby stars with a considerable amount of precision. You might land on a different continent, but definately Gaia. The universe expands at a rate which has been determined (though I fail to remember it.) By capturing our relation in regard to the rest of our galaxy and the one closest to us, we should be able to triangulate our velocity and rate of acceleration. Certainly we won't send a living thing first, an easily recognizable rock structure (Stonehenge? =P ) should serve as a marker of our success.

---

    Kaatnut: You really shouldn't look at the whole space/time coordinate deal as more than a representation. It still is one rock, just as your mousepad is a solid composed of an infintessimal number of slices across the X and Y axes.
    All this is also highly dependant on our idea of a 'time machine.' If we are talking about a box that merely beams our (insert futuristic-sounding sub-nuclear particles) to X,Y,Z,T; then we have a problem. But, since we are talking about science fiction anyway, why not send them in a parcel which is bound to something constant, say the north pole? If the sub-atomic packets were magnetically charged, they would stay above it, regardless of environmental conditions. Assembly is our only problem.
    Realistically, the only way any of this could work is if a receiver is built now and the sender is used to project data to said receiver (which compiles it.)

    In reference to Inherent impossibility in science fiction time travel, the butterfly effect on such a small scale is bogus. The oceans and earth-temperatures are a large enough buffer to make up for our superhero breaking a sweat in 1375.

I don't understand something here, please explain.

If I understood right, according to Newtonian Mechanics, there is absolute space, absolute time, and buncha stuff, each having coordinates of x-y-z-t. When there's rock standing still, there's really bunch of rocks that all have same x-y-z but different t. When there's rock thrown, there's actually bunch of rocks that have x-y-z that vary but are close to each other when t's are close to each other. Right?

And, if I read theory of relativity (excellent node btw, exactly what this place needs) right, Einstein's deal is the same, except that when single object "observes" world around it, its x, y, z and t-axises aren't parallel to objects' corresponding axises. Right?

Or, in other words, if you have car driving on top of train driving on ground, in Newton's system you say "ground doesn't move, train moves, car moves faster". In Einstein's system you don't say "ground doesn't move", you say "train moves relative to ground and car moves even faster relative to ground". So there isn't any static, absolute frame of reference.

So what I'm saying, you ask. Well... when you say "I want to be here 700 years earlier", in the light of above, I wonder, what does that mean? So, erosion eats ground so you'll have to adjust for that, you say. Then you say that earth rotates around the sun, so you'll have to adjust for that too, to calculate earth's location 700 years ago. Cool, I say, then proceed to ponder "But doesn't the earth-sun system move too, rotate around our galaxy? Doesn't this galaxy travel around? And is our galaxy part of some larger group that moves too? How can we ever know just what is moving, where, and how fast?". But more importantly, I ponder, "but didn't the above say that isn't any static frame to 'move' against?".

So I try to transcend the boundaries of local observer, but I can't, because any viewpoint would be "local". It would seem that there simply isn't any absolute direction of time and space. So what does "I want to go back 700 years" mean? Where do you end up? Is this motion even defined?

FTL travel and time travel appear to be two sides of the same coin: solve one, and the other is solved.

Why do we not keep our universal x,y,z co-ordinates (a fallacy, but will serve to prove my point)? Simple - gravity. If time travel is non-instantaneous (eg: 1 year/sec) then gravity should keep the time machine in the same place, as to the outside observer the time machine is not moving (it has always existed there).

I think so, anyway. All of this temporal mechanics gets me confused...

What exactly is facilitating your time travel? The original author and several others assume that the temporal traveler is presented a gateway with a little dial. He sets the dial to "-4 months" and hits the red button; the gateway is filled with an eerie blue radiance and the traveler steps into the past and rethinks his investment strategies. Note that the gate only had a dial for time.

Back in the real world, that's not how time works. Granted, if one takes the existence of a physically impossible device such as the gateway time machine presented above as an axiom for the purposes of an example, the example is not consistent with physics. It's like saying, "Let's assume that two plus two is not equal to four. Look! Math is broken!" Of course it's broken; you broke it with your assumption.

So what would a more realistic time machine look like? Two possibilities spring to mind:

• Moving faster than the speed of light. Strap those kryptonite reactors onto your spaceship and give it the greater-than-infinite thrust it would take to exceed the speed of light so time for you relative to the rest of the universe comes to a standstill and begins moving backward. Pop back out of FTL mode and you're however far you got in space and time. It makes sense to an observer standing in another reference frame, but you'll get into all sorts of sticky situations on board the ship, such as the need to hit the brakes before you've started. Or something like that. Fortunately, the situation should never arise, as thrusters that provide more than an infinite amount of power are in short supply. If you find one, call the FBI so they can perform an immense cover-up and cause you to disappear forever.
• Hopping into a wormhole. Read all about wormholes at the appropriate node, but in a nutshell, they are bridges between two points in space-time. That means that somewhere in the universe, there are two magical orifices that are somehow connected: fly into one and you'll come out the other. They are, if you will, a bridge that makes distant points adjacent. The catch is that the universe doesn't distinguish between space and time: when I say distant, I mean points far apart by our definition of space as well as time. That means that one end may be thirty billion years in the past or future as well as four hundred light years in some arbitrary direction. So of course you won't stay in the same place relative to the Earth, but you're in a pretty damn strong spaceship anyway or you would have been crushed by the wormhole's gravity field.

Remember, the universe has no conception of space independent of time. The inconsistency arises not with the fact that the Earth is orbiting the sun is orbiting the galactic center is orbiting the universal center, but with the assumption that such a thing as concrete position without time even exists. If a time machine has a dial for time, it had better also have a couple for position.

I usually don't like to post responses to other writeups but there is one important point that needs to be made here. Many people are saying things like "Everything in the universe is moving at high speeds. If you moved through time and remained in the same place, you would be nowhere near the Earth." They are ignoring the meaninglessness of phrases like "high speed" and "same place" without a point of reference. Someone said the point of reference should always be the center of the universe? We aren't even sure the universe has a center.

The fact is, motion and position are never absolute. But acceleration is. Acceleration is always coupled to a force, which requires energy. That's why, no matter how fast or in what direction we're moving, we continue moving in a straight line (or a gentle curve because of things like gravity) called a trajectory. If whenever you used a time machine you jumped a couple grillion light-years off your current trajectory (or your trajectory extended back into the past), it would require, how do you say?, a shitload of energy to produce a force to cause that massive acceleration. If your time machine did nothing except move you through time, you would stay on the same trajectory you're following now, the one parallel to that of the Earth.

It's true. You can't use a time machine to visit the 13th century; I tried and it didn't work.

Centuries before the time I entered graduate school in 2345, physicists had already worked out the theory of time travel; it remained for the engineers to put it into practice. Time travel was the life's work/obssession of my thesis adviser, Dr Slump. Slump had figured out a way to generate enough negative energy to make wormholes big enough to send something the size of, oh, a cocktail olive through. In fact, in his first practical demonstration, he sent a cocktail olive from the Alumni Club to the Physics Lab.

Unfortunately, in addition to the martini that olive had come from, he'd drunk four others, and the olives had to go somewhere. First, he sent an olive to Tibet, surprising the bejeezus out of a yak that happened to be passing by. His next stunt was to put an olive in an unspeakable part of the college president's wife's anatomy. Fine control demonstrated there.

And then, Ol' Slumpy outdid himself. He decided to send the last two olives to Alpha Centauri. With three sheets to the wind, we all forgot that space was a vaccum. And that wormholes contained a bit more space than they appeared to. So Slumpy turned the dials, opened up the wormhole, and sure enough, the olives went through, as did a jar of toothpicks on the bar, then a bottle of vermouth, then my wallet, then the whole bar, followed by the hapless Professor Slump. Fortunately for the rest of us, the wormhole slammed shut when the wormhole generator went through.

Anyway, the College President shut the project down. Of course the military bought it all up but that made everything classified.

So there we were, Slumpy's students with our half-written theses, and all of our equipment, confiscated by Marines. One of my friends was lucky enough to emigrate to India and get one of the few jobs a bachelor's degree in physics qualifies you for, technical review of science fiction movie scripts. Some of us worked on synthesizing element 200 for awhile but most couldn't stand the tedium and flunked out.

While waiting for my Indian work visa, I was working as a short-order cook in the next town over. One day, a really weird guy walked into the diner. A magenta pinstripe suit really stood out in a place catering to hoverdrivers, waldo operators, and utility bots, the kind they use to clean out the sewers. As Mr Magenta walked up to the counter, Sid, my boss, asked, "Whaddya want, we only got plain coffee, no fancy ass crap."

"I'm not here to order anything.", said Magenta. "I'm looking for a Philip Haplax." Meaning me.

Sid lit up a CancerStik and furiously puffed clouds of smoke in my face. "This one of your friends from over at the college, Haplax?"

"Never seen him before, Mr Sid."

"That's a line of bull. What're you gonna do. try to thrill the waitresses with olives?"

"I'm looking for the owner of this." Magenta threw something on the counter. My wallet.

I was about to say something original like "My wallet!" when one of the bots rolled up and put a grappler on Magenta's shoulder. WE DON~T SERVE NO NOVELLE CUISINE HERE BUDDY. it voked. ALTHOUGH I~M SURE SID IS WILLING TO CHARGE YOU 50 CREDITS FOR ONE SHRIMP ON A PLATE. Magenta knocked the bot over, setting off its gyro alarm. Not a small feat considering it weighed two tons.

DBIONTG DAIBNUGSWEH!I!R RID~IMN GPDRIENSGSW IHNIGR RCDHIANRGGDEISN!G wailed the bot as its treads futilely spun. Two of its friends came over and grappled Magenta's arms; he threw them both. Now there were three bots on (or, rather, in) the floor, dinging and whirring and calling for their lawyers.

"Now just waitaminute!" yelled Sid over all the whirring and dinging. "You wanna start the Bot Wars all over again? Lookit the hole in my floor!" He picked up the phone, to dial the police I suppose. "You brought this purple goofball in here, Haplax, you can go to jail withim! Not only that, you're fired!"

Magenta grabbed my wallet and then hauled me over the counter. I almost regained my balance but he pulled me over one of the flailing bots, and then into a table. As he dragged me across the pavement, other parts of my body met (among other things) a light pole, a FidoHydrant, and a NylaTree. Eventually I was pulled into a hovercar.

Now, this was no ordinary hovercar. This almost looked like it could be something generated in Hyderabad for a science fiction movie: sleek black with a million small protrusions, tapering to a point forward or backward. Fastened to the back seat, with half my body screaming at me in pain, I could see the controls were like no hovercar I'd ever been in. A tremendous acceleration hit me and I passed out.

---

I awoke to a sudden jar, and a stream of curses in a language I'd never heard.

"Where are you taking me?" I asked. Not very original, but I had just been kidnapped and lay glued to a seat, in excrucuating pain. You can understand why I was not up to my usual standard of witty banter.

"You're going to undo the mess you made of my life."

"I've never done anything to you! I've never even met you!"

"Damn ignorant Earthling. Let me tell you just how you screwed up my life."

"For years now, FLrnQSHP has been the only girl (or reasonable analogue) in my life." Like something out of a bad science fiction movie. The guy was obviously nuts, but I was glued to my seat, so there was nothing to do but humor him. "One night, the very night I was to propose to her, I was cruising past Alpha Centauri when something holed my hull. Running to get the patch, I tripped over this." Magenta held up a half-empty bottle of vermouth. "Later, I found the thing that caused it." Reaching into a pocket, he pulled out something that looked exactly like a toothpick. Well, actually, it was a toothpick. I was beginning to get a bad feeling.

"It only took ten timespans to fix the hole, but the incident put me far off course. By the time I reached FLrnQSHP's planet I was thirty timespans late. FLrnQSHP demands puncutality, so the date was off to a bad start to begin with. I thought the ring might cheer her up. Her eye lit up as I handed her the box." Magenta's face took on an almost wistful look, but soon darkened, to a rather dreadful mauve. "She opened the box and found...this." He waved the wallet in my face.

"It took me a thousand timespans to figure out where the wallet came from, and another thousand to calculate where the ring had been displaced to. So, you're going to go fetch my ring. If FLrnQSHP doesn't forgive me I'll pulverize your miserable rock."

"So where's the ring?" I asked.

"It's on this miserable excuse of a planet, but not now."

"Not now?"

"No, it's about two hundred million timespans in the past."

Now I knew he was making it all up. "Oh, come on. They make up better plots than this in Bijapur."

"You don't believe me? Look out the window."

We were out in space, looking down on the Earth. Now, I wouldn't have recognized the view below as the Earth except for the fact that I dated a paleogeography major back as an undergrad. A weird paleogeography major, who'd make a little game of playing hard to get unless you recognized the outline of the right ancient continent. I know the Triassic Period like the back of my hand.

"Two...hundred...million?" I thought, with visions of ducking dinosaurs while searching for a little diamond ring.

"Eleven hundred Earth 'years'."

"Then why are we back in the Triassic?"

"Because I can't take my ship to that year! Every time I try to jump there, something makes me bounce back five hundred trillion timespans! Too much of an anachronism, I suppose, So you'll have to do it for me. But after several attempts, I found I can get close, if I get a running start from back here. Here's a picture of the ring." He stuck something in my pocket and turned back to the console. "Prepare for another jolt."

Some jolt. I passed out again.

---

I awoke with my face in the dirt, and someone prodding me in the back with a stick. I tried to say "Stop poking me" but all that came out was a moan.

"Thae roabearz heafen besmoten thae poarredge neghonto detthe. Heolpenme brothair." Two pairs of arms lifted me; the pain was enough to put me out again.

I returned to consciousness with more Middle English in my ears. "What's a guy gotta do to get an aspirin and a glass of water?" I muttered. The voices stopped.

"Utter not your spells, we have your talismans." In my haze of pain, my brain was converting the voice into some weird Elizabethan dialect.

"I only asked for a glass of water."

"Thou seekest to turn our water to glass?"

"I'm thirsty. For the love of God, give me water."

"For the love of God, indeed. Brother Gilbert."

"Yes, Brother Cymwael?"

"Give the patient some water." Someone poured a moldy-tasting liquid down my throat. "You will soon experience God's wrath, witch."

"I'm no witch!"

A chuckle. "Innocence is the sure cry of the guilty. In this case, a pathetic defense. As I said, we have your talismans. Pieces of bark with writing, and strange symbols as well. Brother, turn the witch so that he can see the proof of his guilt." As Brother Gilbert lifted me, a balding man in a brown robe came into view. He was holding up my driver's license.

"Now, 'Date of Birth' is legible enough, but the arcane symbols beneath are indecipherable." His voice sounded exactly like Ol' Slumpy discussing negative energy. Knowest thou thy birth date? Thou lookest to have about twenty summers, I shall guess "

"Um."

"Small matter. This other...talisman frigtens me. " He held up a brownish rectangle. "Gold Master Calling Card. This is the device by which your Master calls you to do his vile bidding? The sigil on the front moves as one rotates it."

"You can keep it!"

"No, I shall collect oddities no longer. Brother Abbott has decreed so."

"Witches have killed our good King this very year, and thou hast caused Brother Abbot to take away my pastime."

"Two thousand three hundred twenty."

"I shall enjoy seeing thee burn -- What saist thou?"

"You asked my birth date. The symbols tell you. March 31, two thousand three hundred twenty. They're not magical items, they're simply things from the future - like me!"

"Thou admittest thy guilt! There is no need for a trial. We will burn you tonight so that you do not contaminate the Feast of Jesus Christ tomorrow."

Tied to the bed, I had no choice but to lie still the brothers came for me that night. As the younger brothers tied me to the stake, Brother Gilbert stood there reading from the Bible. But he paused and said, "Young man, we burn thee so that thou hast a chance of reconciling with God. The fire will cleanse the demon from thee, thou wilt feel it. Before thou expirest, accept the Savior into your heart. Here is one of Brother Cymwael's oddities, Brother Abbott has decreed it be unmade in fire." He placed something around my neck. Then he continued in Latin and the brothers started to light the brands. Flames rose around me and I passed out again.

---

I awoke, briefly, to an immense roaring sound and two immense grey things slammed the ground on either side of me.

Someone held something wonderfully cool to my forehead as I came to. I opened my eyes and a vision appeared before my eyes. The most beautiful woman I'd ever seen was holding a wet cloth to my forehead.

"So, Earthling, you did it." said a familiar voice. Magenta. I was in Magenta's hovercar, or whatever it was. "You almost didn't make it, with that Tryannosaurus nearly stepping on you." "Where'd you find the ring?"

"The ring?"

"It was hanging on a string around your neck!" said Gorgeous.

"Oh, that. Someone gave it to me in the heat of the moment."

"I'll say." said Magenta. "Your uniform has holes burned in it."

"It's not like Sid's going to dock my pay." So I told them what had happened on December 31, 1199.

"Ok, I understand now. Whatever was keeping me out of the year 1200 kept you out, as well. Once the moment arrived, you were kicked back to the Triassic, Wallet, ring, and all."

"Cretaceous."

"What?"

"Tryannosaurus lived in the Cretaceous. 100 million years - 50 trillion time periods - later."

"Whatever. Anyway, FLrnQSHP loves the ring and has forgiven me. Now I guess I there's no need to pulverize the Earth."

"But it would be so much fun!" said Gorgeous, err, FLrnQSHP.

"You'd rather I not live up to my agreement?"

"From what I hear, you never agreed not to pulverize the Earth."

"Give me that vermouth?" I pleaded.

"OK, then, let's do it.", said Magenta, and cackled diabolically.

---

"Cut!" yelled Director Mani Hrishikrishnan. "Wrap it kids. Good job, Phil. Slump, try not to cackle diabolically in the future."