Larry's Take on Time Travel

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The Grandfather Paradox

Michael J Fox and Christopher Lloyd were outstanding in the film, Back to the Future. The other time travel science fiction classic from the 1980s, Bill & Ted's Excellent Adventure, was pretty cool too.

With the exception of these two movies, and of the Dr Who series on BBC, the time travel genre usually leaves me with the feeling: Give me a break!

I'm giving Dr Who a free pass, because it's a sci fi comedy. Tom Baker understood that better than any of the other Doctors. Here's a famous line, from an episode in which he confronts an alien shape-shifting cactus. (The cactus has temporarily copied the good Doctor's appearance.)

"Why is a good-looking guy like you trying to take over the universe?"
(Not an exact quote.)

I have good company in my skepticism about time travel. The late Science Fiction writer, Robert Heinlein created a story, All You Zombies, which is a long reductio ad absurdum about time travel.

Like most of the well-known arguments against time travel, this story relied on the Grandfather Paradox. You travel back in time, alter the past, and then that action is supposed to have some effect on your life in what you regard as the present. And Heinlein beat it to death.

Of course, there's a way out of the Grandfather Paradox. You can assume that the past is essentially immutable. You try to make a difference, for example by alerting the Secret Service in mid-1963 about the impending JFK assassination in November. But Fate intervenes; the secret Service agents don't believe you. And that particular tragedy happens on schedule.

This interpretation of the Grandfather Paradox allows you to look, but not to touch--at least not too hard.


Mr & Mrs Heinlein, 1980
Mr & Mrs Heinlein, 1980 | Source
Sue, the T rex from Field Museum of Natural History, Chicago.
Sue, the T rex from Field Museum of Natural History, Chicago. | Source
Dr Who's TARDIS (time and relative dimensions in space).
Dr Who's TARDIS (time and relative dimensions in space). | Source

Legitimate 'time travel'

Scientific investigation allows us to travel into the past, in a metaphorical sense. We look at the evidence with which Nature provides us, and then we make informed conjectures about the distant past. Then we gather more evidence in order to test our hypotheses. A classic example of this process is the ongoing postmortem on the disappearance of the dinosaurs 65 million years ago.

Physicist Luis Alvarez articulated one of the popular explanations: a big asteroid impact. This theory is consistent with a couple of facts.

First, there's a iridium-rich layer in the geologic record. And it dates to approximately 65m years ago, which coincides with this particular extinction event. Aside from this layer, concentrated iridium is relatively rare on Earth, but is somewhat more common on meteorites.

On a side note, metallic iridium is interesting in its own right. It and osmium are the two densest known chemical elements--a bit denser than gold even. Moreover iridium, like gold, is not particularly reactive in a chemical sense. Gold, but not iridium, will dissolve in aqua regia, a mixture of concentrated hydrochloric and nitric acids, in a 3:1 molar ratio. But I digress.

The second piece of evidence is the Chicxulub impact crater, which is partly in the Gulf of Mexico and partly on the North end of the Yucatan Peninsula. The age estimates for this geologic feature are consistent with the expiration date of the dinosaurs.

Here's the story in a nutshell. A medium-size asteroid impacts Earth. This sends a huge volume of dust into the atmosphere, where most of it stays for many years, blocking a significant fraction of the incoming sunlight. The upshot: a very long 'Asteroid Winter.' Since dinosaurs were highly specialized, they could not adapt fast enough to the sudden climate change. The die-off left vacant ecological niches that were gradually occupied by evolving generalist species.

The impact theory is not the only game in town. At the same time, otherwise edible plants were beginning to synthesize poisonous alkaloids. It's thought that the vegetarian dinosaurs could not taste these bitter substances, and were poisoned by the plants. Then the carnivorous dinos, who ate the herbivorous dinos, lost their favorite foods. Or so the story goes.

Of course, it's possible that the dinosaurs were done in by a double whammy--the impact and the alkaloids.

Science is much more than a consensus of 'experts' on a collection of stories about the natural world. The scientific process is similar to taking a vacation. The journey is half the fun. Except for the part about getting violated by TSA employees. :-(

The main point of this section: Paleontology is a way to explore the distant past, without the benefit of Dr Who's tardis (time machine). The study of Natural History is a legitimate form of time travel.


Artists conception of Ptolemy.
Artists conception of Ptolemy. | Source
Solar system
Solar system | Source
Antikithera mechanism
Antikithera mechanism | Source
William of Ockham
William of Ockham | Source

Time travel survey

Do you think that it's possible to physically visit the past in a time machine?

See results without voting

Larry and Occam's Razor

Dr Who could set a destination time and a destination place on the control panel of his tardis. (I'm not sure why he ended up on Earth half of the time--even when he intended to go elsewhere.) Now what about the case where we set a destination time and a default destination place: the point from which we started?

Scenario 1. Our starting point is on a grassy plateau, which has been rising very slowly in the recent geologic past, because of incipient mountain-building. Right under our feet, two tectonic plates are colliding, which causes them to warp and uplift--very slowly, of course.

Given the same geographical coordinates (latitude, longitude, and altitude), where will our time machine materialize? Will it suddenly appear in the air, and then crash to Earth? Or will we avert a crash landing, because we materialize on top of a tree, which had previously existed in a different climate at the same location?

But that's all very Ptolemaic. In the outdated Ptolemaic Theory of astronomy, the Earth is the center of the Universe, and everything revolves around the Earth. As a scientist, I cannot prove that this picture is wrong. However it's needlessly complex; there's too much excess baggage. It's much easier to predict future locations of planets, by assuming that they all have elliptical orbits around the center of mass of the Solar System.

The famous Antikithera Mechanism, recovered from an ancient Greek shipwreck in the early 20th Century, was apparently the world's first analog computer. It allowed the ancient Greeks to make basic astronomical calculations about some familiar heavenly objects that were visible to the naked eye. And it did so without benefit of our modern Heliocentric (sun-based) understanding of the solar system. That's quite remarkable!

Here's where the principle of Occam's Razor comes in. It says: Given two 'competing' scientific hypotheses having equal predictive power, the simpler one--like the Heliocentric Theory of the Solar System--is better than a more complex one--like the Ptolemaic Theory.

My objection to time travel will become apparent after we explore two more time travel scenarios. With all due modesty, I'll call it Larry and Nell's Razor.

Scenario 2. Your new reference frame is the sun, in accordance with the Heliocentric Theory of the Solar System. You twiddle the dials of your time machine to go back 6 months into the past, and to arrive at the same physical point from which you started.

Oops! You've just arrived at the point where the Earth was at that time. You can't even see our fair planet, because it's 'hiding' behind the sun. But that's only a first approximation. Hold onto your hat; it gets better.

Scenario 3 is a bigger picture. Our Solar System is in orbit around the center of mass of our galaxy, the Milky Way. If we attempt to travel back in time, we may even end up outside the Solar System!

We could create additional scenarios on even larger scales if we wanted to, but I think that you're beginning to catch my drift. Attempting to travel back in time to our exact same starting coordinates has no meaning. Why? Because any theory of time travel must have a stable coordinate system for location. And such an absolute frame of reference does not exist!

No matter how much information we have, we cannot predict the wayward path of a time machine, once it's switched on. Since prediction (and hindcasting in the case of mining geology) is the coin of the realm in the physical sciences, a meaningful theory of time machines that visit the past is not possible. Not until we actually build one, and take it for a test drive--assuming that this can be done.

According to this section of the Wikipedia article, others have thought about the problem of time travel without space travel, but have come to weaker conclusions. And very few Science Fiction writers have come to grips with Larry and Nell's Razor.

Copyright 2013 by Larry Fields

Infrared photo of the core of our very own Milky Way Galaxy.
Infrared photo of the core of our very own Milky Way Galaxy. | Source

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Comments 16 comments

WillStarr profile image

WillStarr 3 years ago from Phoenix, Arizona

In 'The Time Machine', Wells points out that our hero is traveling in time, and not space, so his machine doesn't move on the Earth's surface (except when stolen by Morlocks, of course). But that ignores both Earth's rotational speed, and its orbital speed around the Sun. I'm afraid that such a time traveler would find himself gasping for air in space, as he watches Earth hurtling away at 68,000 miles per hour.


Larry Fields profile image

Larry Fields 3 years ago from Northern California Author

Hi Will. Exactly. Thanks for stopping by.


Nell Rose profile image

Nell Rose 3 years ago from England

Hi Larry, can I call in Nells Razor too? lol! I have often sat down with my family and talked our way through this too! me and my brother are boffins, sorry! haha! we talk the talk but sometimes we get into arguments such as, the scientists say if we did go back in time it would actually be to another dimension exactly the same as this one, then I would say yes but it doesn't stop you floating through space yelling wheres the darn earth? Here's a thought though, how do you know that nobody has gone back in time? what if the paradox theory doesn't work and actually the first time round kennedy was saved only to have someone go back and kill him? we wouldn't know any different would we? lol! that argument took all night I can tell ya! great hub Larry, and right up my street! voted and shared, nell


Bronwyn J Hansen 3 years ago

Hi Larry. There is only one way to travel through time and space - in an English police call box :)


Larry Fields profile image

Larry Fields 3 years ago from Northern California Author

Hi Nell,

Nice to hear from you, as always. Great minds think alike! Of course, you're welcome to share in the glory--or the notoriety--as the case may be. Thanks for the share.


Nell Rose profile image

Nell Rose 3 years ago from England

Just been watching Down the rabbit hole, what the bleep? its the most fascinating set of dvds I have ever seen, if you haven't watched it you really must get it, the part about praying or sending out good thoughts to water and making the molicules change shape is amazing!


Larry Fields profile image

Larry Fields 3 years ago from Northern California Author

Hi Nell,

When in graduate school, I took a course in Quantum Chemistry. I was very impressed by the fact that a minimal set of assumptions could lead to exact predictions for the interactions of light and individual hydrogen atoms. And when we studied the famous Double Slit Experiment, I remember thinking: Wow; that's really spooky!

Unfortunately, I never did learn where the initial assumptions came from. I was also disappointed that for slightly more complex atoms--like helium--you need to start using approximations. And even calculations involving relatively simple molecules can take much computer time.

Much as I like Physical Chemistry, I decided that it wasn't for me. During the entire course, I did not have a single idea about future research projects in that area.

So I decided to go with a more applied specialty, Analytical Chemistry (measurement). And that turned out to be the right decision. My major professor, Steven Hawkes (from London), and the other people in the Analytical Division were very supportive of my desire to do a research project that was truly independent.

My impression of science reporting is that the quality is generally quite poor. That's partly because science journalists have deadlines, and partly because many scientists like to 'spice up' their findings for the Great Unwashed.

I have nothing against drawing parallels between science and New Age belief systems. But my impression thus far is that these attempts are not done in good faith. All too often, scientific buzzwords are thrown in to lend status to questionable spiritual claims.

If we ever get together in person, I imagine that we'd have a long discussion about this. And I would look forward to it.

It's nice to hear from you, as always. And thanks for stopping by.


Larry Fields profile image

Larry Fields 3 years ago from Northern California Author

Hi Bronwyn,

I agree that the English police call box was a nice touch. But The Master--if he's still around after all of these years--traveled around in a classical Greek column. Like you, I'd definitely feel safer as the good Doctor's companion.


Mitch Alan profile image

Mitch Alan 3 years ago from South Jersey

With TARDIS we have the acronym Time and Relative Dimension in Space. To calculate the coordinates for time travel, one must account for the "Relative Dimension in Space" as well as the "when". If we calculate where the earth was at the time we want to visit, then, in theory, we could determine our desired "where/when'' to program into our own TARDIS.


Larry Fields profile image

Larry Fields 22 months ago from Northern California Author

Hi Mitch,

Thanks for your comment. You wrote:

"If we calculate where the earth was at the time we want to visit . . . "

There's a fly in the ointment: The Earth's location is meaningless in an absolute sense. Why? Because the Universe, unlike the Who-niverse, does not have a coordinate system.

We could talk about Earth's position, relative to the sun. But the sun's position is also meaningless in an absolute sense.

Ad infinitum.

If you have a solution to this problem, I'm all ears.


Mitch Alan profile image

Mitch Alan 22 months ago from South Jersey

Arguably and understandably the plotting of the "Anywhere and Any When" scenario seems unattainable, but what about on the earth alone...it would obviously be a mathematical endeavor of incredible magnitude, but undoable?

Do we not now factor the location of where Mars WILL be when we launch an exploration? Do we not have the ability to know where the earth will be when returning from the moon? I know these are relatively short trips in the big picture, but wouldn't the calculation be along the same principle?

I'm not arguing ease or even practicality, but simple possibility...are the calculations, at least for known targets like earth, possible (assuming computing power that is virtually unlimited) if not practical?


Larry Fields profile image

Larry Fields 22 months ago from Northern California Author

Hi Mitch,

Good points. Another possible fly in the ointment is a consideration from Special Relativity. My limited understanding is that under certain circumstances, it's not possible for two observers in different locations to agree on whether two events occurred simultaneously. If so, that throws a monkey wrench into everywhen. It'd take more than a sonic screwdriver and my long scarf to get me out of that quagmire.


Akriti Mattu profile image

Akriti Mattu 18 months ago from Shimla, India

Your posts are so innovative :)


Larry Fields profile image

Larry Fields 18 months ago from Northern California Author

Hi, Akriti. Thanks for stopping by.


nicomp profile image

nicomp 15 months ago from Ohio, USA

I love the term "Legitimate 'time travel", as if there's another kind.


Larry Fields profile image

Larry Fields 15 months ago from Northern California Author

Hello, nicomp. It's nice to hear from you!

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