Has anyone wondered about the way Michael J Fox travels back in time?

Marty McFly's Delorean starts travelling back in time once it reaches 88 mph.

This means that when it is at say 90 mph it is already travelling backwards through time. Now lets look closer to the magic 88m ph - Where is the Delorian at 88.0001 mph ?

The logical answer is it is very close to the Delorian at 87.9999 mph (remember the faster Delorian is travelling backwards through time so will co-exist with the slower Delorean just like Marty co-exists with himself later in the film).

Following the logic as we get closer to 88 mph the physical distances between fast Delorean and slow Delorean get less.

So what happens when Marty first exceeds 88 mph ? - KABOOOOOOM

Marty and the Delorean will have atoms that are overlapping, a nuclear fusion reaction should take place and Marty would take out a significant proportion of the United States.

One possible workaround this is that he "instantly jumps" back in time when he reaches 88 mph. If this is true then no Kaboom, but unfortunatly no planet Earth (well it still exists, but it will no longer be where he is !)

As an example, imagine that I could jump back in time just 1 hour. If my location in space remained the same I would travel back in time allright, but I would either be several miles up in the sky, or below the surface of the planet. In Marty's case the more likely outcome would be many millions of miles from planet Earth - ie he will miss the ball.

Phobos

<font size=-1>[ This Message was edited by: Phobos on 2002-07-26 21:46 ]</font>

Interesting questions!

What if Marty was travelling west to east? Would he gain the benefit of earth's rotational velocity? What if he was going west to east at midnight: does he gain the benefit of the earth's orbital velocity?

Fun movie, but ya gotta check your brain with your coat and brolly!

Silas

Yowsers, Phobos! [img]/phpBB/images/smiles/icon_eek.gif[/img]
That's some pretty darn good thinkin' there.

And you're right, that would be a problem, wouldn't it? (On all aforementioned accounts.)

__________________
"As I lay beneath the Southern Cross, the stars tell more than I could" . . . David Meece

Also if he was towards the equator would he travel faster in time than if he traveled near the poles? Since basically the equator rotates faster than at the poles (that is why all of the NASA and eurpoean space agencies try to launch as close to the equator as possible.)
Plus the faster he gets does he go farther back in time? EX. it takes 88mph to go from 1985 to 1960 something. So to go to ancient times, does it take greater amounts of energy and speed, or does it take the same amount of energy and speed? Like if they wanted to go back to the triassic, would they have to get the energy output equal to the sun?

P.S. Stupid north american here, but what is a "brolly"?

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GIYUL :-)
"It takes Thousands to fight a battle for a mile, Millions to hold an election for a nation, but it only takes One to change the world." - Dan Sandler 2002

The way I've always seen it, the 88mph is simply a critical point. below that, there's no action, but when you reach it, everything happens instantly. So at 79.99mph, Marty is in his own time travelling at good clip. And there is no 88.01mph, because the reaction has taken place before that and sent him instantly through time, where he starts to slow down again. The "distance" in time is immaterial, all the energy goes into reaching that critical point, breaking the barrier, so to speak. Once you breach it, you can go anywhere.

As to the Earth being there when you arrive, well there's a trickier question. I have considered it myself, and even considered writing a short story about it once. A kind of "oops, forgot to take that into consideration" story. And you don't even need to give it an hour, considering that we are moving at thousands of kilometers per second. Even a millisecond would be enough to throw us off the face of the Earth.

But then I thought about it some more. It all centers around relativity. The problem all centers around the idea that the jump is discontinuous, that the time traveller keeps his current velocity and vector when he jumps, and so the Earth moves out from under him, so to speak. But then, what is he maintaining that velocity relative to? Is it the cosmic background radiation? The local group? Does he break with everything when he jumps? I have a hard time picturing it, though that's probably just my poor grasp of physics. [img]/phpBB/images/smiles/icon_smile.gif[/img]

So I can see a couple of ways around it. In the first one, when the time traveller jumps, he keeps the velocity connection he has with the universe. He continues to "stay with the Earth" as he moves through time, even though that jump is instant. It's more like an instant fast forward than a discontinuous jump. Although I can see problems with this model too (What happens when an object moves through the space occupied by the moving time machine? Why doesn't the passenger age as well?, etc.).

Or perhaps, and more likely, the time machine itself is able to take the spatial considerations into account as well. You've created a machine that's able to move through time, surely it's powerful enough to compensate for the movements of the universe as well.

In short, it's only a movie. If time travel didn't work ouf in that universe, it would be a very short and uninteresting story (New title: Marty goes Boom!).

Now, let's not get started on the time-paradox question, ok?

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<font size="-1">PLEASE NOTE: Some quantum physics theories suggest that when the consumer is not directly observing this product, it may cease to exist or will exist only in a vague and undetermined state.</font>

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<font size=-1>[ This Message was edited by: David Hall on 2002-07-27 03:00 ]</font>

One of these ...



The word is just a shortened version of unbrella - In the UK we use them a lot to protect us from the blazing sun (no rain over here) [img]/phpBB/images/smiles/icon_cool.gif[/img]

Phobos

You've put your finger on it, Phobos, but you've got it backwards.

It is not the case that as he jumps in time at 88 mph he will cause a large explosion.

The mechanism is set up (and tested with smaller test masses) so that it is "synchronized" with the Earth's surface in spacetime. It could make the jump at any speed--but because of the very effects that you are worried about, it has to be going 88 mph or it will cause an explosion. Actually more of a "blast" in spacetime, but it could still be ugly.

Happened to me once. I experienced puberty for five minutes when I was 43. Whoa.

wow - that means in just six years time I could be a grown up too !

Phobos

[quote]
On 2002-07-27 04:51, Phobos wrote:
And exactly which dimension do you come from? [img]/phpBB/images/smiles/icon_smile.gif[/img]

__________________
"As I lay beneath the Southern Cross, the stars tell more than I could" . . . David Meece

The idea of the Earth moving away while you're time travelling is one that always let's otherwise thought-stimulating time-travel (*snort*) movies down. HOWEVER, if you COULD time-travel, then you could "jump" through time and measure the change in distance between things like the Earth, the Sun, the stars without having to worry about your own motion (because you cease to exist while time-travelling)! At last! An external frame of reference!
Wooo!

At least, for the time being.

Okay... here's a good Back to the Future question:

When Doc Brown and Marty travel to the past and then back to the future, the changes they make affect the future they return to. So, in the first episode, his parents are "cool" when he returns.

In the second, however, when Biff steals the time machine to give the almanac to young Biff, he returns to the same future he left from! Shouldn't the future he returned to have been altered to account for young Biff having the almanac?

Maybe it is a different dimension, and he is not actually time traveling.

__________________
GIYUL :-)
"It takes Thousands to fight a battle for a mile, Millions to hold an election for a nation, but it only takes One to change the world." - Dan Sandler 2002

Funny thing, I saw BTTF 3 at the movies, and TNT/TBS shows BTTF 1 about once a week or so, but I have never seen BTTF 2 all the way through. I smell a conspiracy at work!:-)

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I am a doctor, but I don't play one on TV.

I think there's a quick line in there somewhere that explains that he managed to get back "before" the time-altering events occurred, so he returned to his original time, or something like that. It's been a long time since I've seen the movie.

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...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

I'll have to watch the movie to know exactly what you mean here, but remember, temporal changes don't happen overnight! Witness the gradual fading of the photographs.

I suspect that B2TF is meant to be a jab in the ribs for all time travel theories, it's just so stooopid! (With the self-adjusting photos and so on...) Not even Steven "Deep Impact" Spielberg could take that sort of thing seriously.

I did something similar in cartoon form, last year:
http://www.geocities.com/toomuchspar...e/timetrav.htm



<font size=-1>[ This Message was edited by: Sarcastronaught on 2002-07-29 06:16 ]</font>

Very nice. Thought provoking.

Especially the disclaimers at the end! [img]/phpBB/images/smiles/icon_smile.gif[/img]

How do you know it was the same future?

You have a good point there. If you notice, in the movie, by the time Biff returns to the 'future', Doc, Marty and Jen are heading back to the car. Already being out of the house.

Who's to say that once Biff returned, it was the 'future' Marty's home still.

Or something like that. [img]/phpBB/images/smiles/icon_smile.gif[/img]

Still, the first "Back to the Future" is one of the three really original time travel moves I've seen. The other's being "Bill and Ted's Excellent Adventure" and "Frequency"

--Fox Cutter
http://www.chaos-keep.com/

I remember the scene - because I had been puzzled by the same question. Although Doc does explain that the time change hadn't caught up to them yet, it still seemed weird that Biff came back to "their" time as is. One would think he would have returned to a new time. But, if that happened, Doc and Marty wouldn't have gotten the time machine back so that they could go back in time. Of course, if Biff did come back to the alternate time, there would be no time machine (because the changes he made ensured Doc never got the chance to make it). So, that would have left an irreconcilable paradox. Then what would you do with the movie?

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"All that is gold does not glitter / Not all those who wander are lost..."

<font size=-1>[ This Message was edited by: nebularain on 2002-07-29 14:54 ]</font>