Seriously?

Counting heartbeats, dripping water, pendulum swings, seasons, moons...

And rocks existed long before anyone had a name from them. As did time. If there were no human beings on the planet, and never had been, cheetahs would still be faster than snails. And "faster" is a function of time.

As with most things that we don't fully understand or perfectly measure, time exists independent of our limitations.

There was a young lady named Bright,
Who traveled much faster than light,
She left one day,
In a relative way,
And returned on the previous night.

When they questioned her, answered Miss Bright,
"I was there when I got home that night;
So I slept with myself,
Like two shoes on a shelf,
Put up relatives shouldn't be tight!"

Lobo, you raise a good question there.

Wouldn't faster be more applicable to distance rather than time? I haven't really seen an Impala check his watch before trying to run away from a cheetah. I have seen a cheetah kill twice and trust me it is worth watching. Excuse the pun but for those few seconds, time really stands still. Very still.

Strange that in your quote from the Year-2008, Cliff, you said you accept time-travel but in your recent post from 2016 in the DC-Marvel thread, you said you gave a presentation at Occidental College to Disprove time travel. Something happened between 2008 and 2016.

By resurrecting this thread, you've allowed me to travel back in time to visit with some old NVMS friends. Thank you Orville.

Interesting question Orville,

WARNING: those not interested in Theoretical Physics will be confused or bored reading this....

I do accept time travel, it would be foolish not to. At least as long as we move forward. The U.S. air force proved in 1974 that time dilation forward is possible with the now famous double clock experiment. Two synchronized atomic clocks. One rock steady on the ground, one flown at mach two or three. After that the clock going at speed had moved forward as compared to the other.

The past is quite another story. When I presented at Occidental college, the first point I brought up with that to travel to the past, you must treat your destination as a place. One that has not existed in however long it has been, and you are saying it still exists. Hawking's explanation, and indeed Superman's, suggest that you are traveling into another universe. There is in fact zero proof of this. Not observational, not mathematical, none. It is simply Hawking (Arguably the greatest theoretical physicist thinker of our time) saying this is possible.

In all situations, when the probability is zero, there is still a possibility. This is more the "dumb luck" factor than science, but anything is "possible."

OK, so we say that a past event, say 9/11 still exists somewhere, and I want to travel back a day or two before it and warn people. I exceed the speed of light per Einstein, and using a very easy but scary looking calculation know exactly how long to travel for to reach my destination. (look up Lorentz time dilation if you really want to see it.)

Wait.... Where is it? Where is 9/11 happening? Not here, I promise. The Earth spins at over 1000 miles per hour. Rotates around the Sun at an amazing speed, the entire solar system rotates the black hole in the center of the galaxy and the universe is expanding. It is possible to calculate where the Earth was at the time of the attack, but it is not easy and I don't want to do it. Suffice it to say it is very far away. A time ship that moves back in time will find it is in empty space where the Earth will be when it catches up.

ON the TV show 7 days, they got it pretty close to right. Frank never got out of the ship 7 days earlier in the same place he started from. He could be all across the country, because of this. (reality is more likely he would be in deep space, not the Mid west, but they did show in the first episode, the first pilot dead and floating in space having failed at the controls)

Now the real problem, the logistical one not theoretical. To go back in time you must exceed the speed of light. By today's technology, that is not even close to possible. The late Carl Sagan designed a ship that could be built with today's technology, and it could reach 30,0000 kilometers per second. (18,600 miles per second) Sound fast? Sure, but that is only one tenth the speed of light. But even if we could travel faster than light, and avoid the issues of mass as outlined in Einstein's famous E=mc^2, The formula that everyone got so excited about that proved you could go back in time? You can only do that by taking the square root of a negative number. The mathematical word for that is "irrational." Yes, it is makes no sense at any level.

So other than the Hawking/Superman idea, I think we are dead in the water and will not go back in time.
Forward? Sure, lets take a terminal incurable patient and send him into the future where the cure exists.

That is the basic of the talk I gave at Occidental College and it went over very well in front of an audience of about 70 or so Physicists. Here I left out the math very much on purpose.
Class dismissed.

Any Questions....

Pardon an inexcusable typo. One tenth the speed of light in metric is 30,000 km per second.

? "u can only do that by taking the square root of a negative number. The mathematical word for that is "irrational." Yes, it is makes no sense at any level. "

what happens when you treat mass as a complex number?

Jonathan, that more or less is what you end up doing. (With result of the velocity not the mass, in this case) It still is not real though. It is a "work around" used by mathematicians and scientists to figure out the value of a number that should not be able to be figured out.

An hypothetical universe which has time travel also introduces large holes in "the observable now". And Time Travellers only areas...which you'd expect to grow without bounds...

It's not like we pass ourselves on the way to work twice a day.

See, this is proof that there IS time travel! You will go back at some time and get the car before it's stolen. Unfortunately, you won't tell your earlier self that you did it, so it will be missing all those years!


[/quote]

I would bring a video camera and record their shows for posterity.

If you watch "Big Bang Theory," there was a "flashback" episode where we see how Leonard ended up in this apartment with Sheldon. (An amazing job by Jim Davis (correct name?) as we see how much MORE repressed Sheldon was before Leonard came into his life.) There is a clause in the "room mate agreement" where Sheldon states that if either of them invents time travel, they will travel back to this moment to tell themselves. After it's initialed, they look around for the time machine and Sheldon states; "Well, that's disappointing."

My idea for the actual last shot of the show is to have them move out. Sheldon is the last to leave and as he closes the door, there's a sound effect and a time machine appears in the empty living room. An older Sheldon and Leonard come out and Leonard snaps; "You see? It's impossible for us to materialize in any place where our past selves are already. Can we go back now? There's a Babylon 5 marathon starting soon!" This will start their last argument as they dematerialize, heading back to their own time.

Some time travel stories do have rules and breaking them can lead to dire consequences. Spider Robinson's series of "Callahan's" stories deal with people who can time travel. (Mike Callahan, his family and Nikola Tesla among them) one of the strictest rules is that you can't appear in a part of the time stream where you already exist! This isn't just the same room, this is the same universe!

A very funny movie about time travel: "Bill and Ted's Excellent Adventure"! The reason for their time travel is to pass their high school history exam (and cause world peace, but that's getting close to spoiling)! Starring George Carlin and Clarence Clemmons among others. Lynn

Rumor has it that a guy named Wells is working on a time travel story ala Mitchell. I'll wait for the whole thing in one book before making comment on the topic. Spoilers?

Stross wrote "palimpsest" in one version of the past. Crichton wrote "timeline" in the version I was following.

There's a continuity issue when reconciling stories...how does it look to observers? . Any ideas?

No. this had the actual thing go back in time to try and cure himself only to create an alternate timeline. They did another where Lockjaw, a dimensional hopping dog takes Ben to a reality where the powers got slightly changed. Ben becomes Mr. Fantastic and Reed becomes the Thing. He's only there long enough for Reed/Thing to let him know how lucky he is... in THIS universe, there's no Alicia.

And what of the places these known alternate universes are so similar as to interfere with each other?

Another issue, Planetary one, with champions of another universe... Quantum computing...

The topic has evolved, with the time-line hypothesis almost completely going the way of luminuferous aether. And some future readers may snicker about vaping - digital smoke and continuity.

:)

I don't know. I haven't seen stories where alternate universes are so similar as to interfere with each other.

(Fear #19, there was a story about alternate universes crossing paths with each other. It turns out the swamp where the Man Thing resides is a nexus point and in fact SOMTHING has to be there to guard against incursions. At this point in the story, the divider had become so weak that things were able to pass into our world. The Man Thing (unknowingly, as he has no mind), and a girl from our world team up with a wizard from another plane a barbarian from yet another plane and, (I'm not kidding here) Howard the Duck, (Yes, this is where Howard first showed up!) Team up to try and stop the invasion and rebuild the barrier.

Nothing to do with time travel, but it was an interesting story.

Back to time travel. I remember one of my favorite moments from "Doctor Who" ("Pyramid of Mars") had the Doctor (Tom Baker) and his companion Sarah Jane Smith (Elizabeth Sladen) stumble across a mystery in 1890's England involving a monster called Sutek the Undying. Sutek had been trapped on Mars and was mentally manipulating people to be freed. Sarah suggests they leave. "We know he doesn't win because we've BEEN to 1974 and nothing's happened." So the Doctor takes her back to 1974 and shows the Earth is now a desolate wasteland. "We are part of that time stream now, Sarah." He explains. "Without us there, Sutek wins."

I mentioned rules earlier. The Doctor has some too. The biggest one is that he can't change and "fixed moment in time." If it's been recorded and observed, it cannot be changed.

My favorite "snarky" moment of the Doctor's has to be; "When A Good Man Goes To War," where the Doctor (Matt Smith, in this case) confronts the Big Bad who smugly exlaims; "You're a good man. You follow the rules!" To which the Doctor replies; "A good man doesn't need rules. Now is not the time to find out why I have so many!"

I was going to post a story here by Spider Robinson, but I just realized posting the story throws up a major spoiler for the plot.

I guess this explains why I am often early.