"The future ain't what it used to be."

Point of reference


If Time Travel was possible, how the the Time Traveller calculate which point in space-time, he or she could travel too? If they were travelling in some sort of stationary machine or otherwise from a point on earth, they would have too ensure that at the specific point they travelled back too wasnt three thousand miles round the other end of the sun?? If u see what i mean?? If i was too travel back one day from my position in space -time at the moment, the earth would have a different position in space whereas i would have the same space-time coordiantes.
So how would this work?? I mean apart from obviousley taking you too a specific point in time and space??
i have never thought of the movment of the earth and a facture of time travel.
i have considered the place of witch you travel. like if you are stationary and you travel back will there be a tree in the place you are at.
i think if you travel ine time you will be at the same speed as the earth.

Yours is a great question Langly.

I'll repeat a thought experiment I did over a year ago on this board.

Look at the end of your index finger and imagine a point in space it represents. Count to ten. Look at your finger again. Where is that original point. Remember:

Regardless of where you are sitting, in the time you counted to ten, the earth rotated on it's axis at the rate of 1200 MPH. The original point is AT LEAST as far away as the distance it rotated in that time.

It also moved a little further in it's orbit around the Sun.

The sun moved a little further in it's orbit of the galactic center.

The galaxy moved a little in whatever direction it moves toward (or away from) some other point that is as yet undefined
precisely in all of astronomy.


If you want to go back 100 years, just WHERE do you think you are going to?

We've already got a problem defining "where" in terms of the time it took you to count to ten. Imagine the calculation involving 100 years. But lets assume it's do-able. Or can we?

Now I'll offer my old challenge. What calculations will you do to solve this?

HINT: Define ANY point (in space time) in the universe that can be defined as a point relative to the rest of the universe. If you can do this, the 100 year (and the "count to ten") calculation will be easy.

If I'm going to get in a "Time Machine", I'm going to be REALLY FUSSY about just WHERE it says it's going to deposit me. Let alone WHEN.

I like this idea you have Lee of defining a point which we could use as a reference point!! But do you have any ideas of what or where the point would actually be?? Aswell as problems such as orbits etc, we also have the problem of the expanding universe..
I can't see any way around "Safe" travel back in time??

Maybe time travel in a space ship would be the safest?? surely there is a good probability that such a means allow us too travel back too at least a point in space we are sure is "Safe" ??

I know this will also provide dangers of travelling back too a point in space time where maybe a planet of meteor existed, but i think this is the safets means??

So what could you use as this point of reference?? the only point i can think of is the big band??

Well i hope we can further discuss your ideas!!

Actually Langly, I have NO IDEA of how to even go about calculating where that point on the end of my finger was ten seconds ago.

But then that was my point. (No pun intended).

The problem is, I have yet to read a treatise by ANYONE who has a solution to this problem.

It's sort of a take-off on the classic 3 Body Problem. In my example, the 3 bodies are the Earth, the Sun, and the center of the Milky Way Galaxy. (With the former point on the end of your finger being the sought after coordinate, using the above 3 as a reference.) Maybe that makes it a 4 body problem. Way tougher yet. Exponentially.

My question is admitedly cynical, but yet to an honest end. Truth is, I'd like to see ANYONE solve this problem. But...

Since it does exist as a very real everyday problem, (in mathematics anyway), it poses a real problem for time travel doesn't it.

Your suggestion of the Big Bang as a starting point (here we go with the non-intended puns again), for reference is excellent and one I've always thought would be a good "given" to use as a relative reference.

Problem is, all of Astronomy, Cosmology, Quantum Physics and Mathematics has yet to come up with a definition of just "where" that event took place. It's a sort of relativity "catch 22" problem in itself in that since (according to relativity), space AND time originated with this event, it is not possible on a conceptual level to actually define a location for such a point. Cosmology says that to attempt to do so is like a two dimensional creature trying to understand 3 dimensional space. A nice analogy, but worthless for the understanding by the average man/woman.

One thing Einstein, Sagan, and Hawking ALL agree (agreed) on is that ANY explanation of the universe should be comprehendable by anyone. Sort of an "Occam's Razor" philosophy of education.


If the "finger point" problem is as yet unsolvable, OK. All that is necessary is to say so. All the hypothetical jargon of how it could be possibly solved by orators endowed with "delusions of self authority", can't make it so.

In other words, skip the bull sh*t and cut to the chase.

I have yet to see anyone define ANY time travel concept I cannot yet come up with a problem that renders it un-doable. No brag, just logic.


I'm not an authority on QM or Relativity, but I do understand enough of each of them to spot when someone is trying to snow me. I know my Hadrons, Leptons, Quark colors and neutrino characteristics. As well as the difference between special and general relativity. But I'm no PHD. None of us needs to be to understand the world around us.

In my view, time travel is not actually possible because of a flawed concept we have of time itself. But that's another thread we can go into elsewhere.


In a previous forum, I posted the following, which relates to this discussion:

"Keeping in mind that the earth undergoes contant changes and is continually moving
through space, I think that most time travelers to the past started out from a
safe 'present' location, but when they reached a destination in the 'past', they
rematerialized inside of a mountain, or underwater, or in a rock, or in outer space.
The rest died from diseases that we have no resistance to. If they arrived safely, then
then they faced to same problems on the return trip."

My point exactly. But I think you give them undue credit for even getting THAT close.

I'd be more concerned about materializing in the void of space somewhere with the Earth or even the entire Solar System nowhere in sight.

The rate of expansion of the Universe is in fact a known quantity. (I've seen it and will try to find the number and post it here somewhere soon.) Unfortunately a clear definition of the so called "direction" is not. "Outward" is the only accepted definition that comes close. Just where we fit into that is really quite vague. This results in some SERIOUS distance over even a year or two. Let alone a thousand. This all AFTER you've factored the Earth's rotation, orbital velocity, and the Sun's orbital velocity around the Galactic core. Plus the fact that this LAST calc is not even constant since the Galactic arms are spiraling in and increasing in velocity all the time.

This gets REAL SERIOUS if you're planning on materializing at the corner of Main St and Elm Ave in Peoria, 4:00 P.M. on Jan 3, 1862 doesn't it! :)


This may seem like a rather silly idea but i've been toying with it for some time.
Suppose we develop a means of travelling back in time where we can keep track of our point in time and space at each instance of travel, say every second. From here we could reajust too ensure we reach our destination. I know i havent explained this very well, but English has never been my strong point?? Maybe thats because im scottish?? Anyway i hope you get the jist of what im trying too say... it would take a hell of a computer program though..

Sure. For the sake of hypothetical argument lets assume this "point of reference" is actually solvable. Lets assume we can forget the positioning problem since we've invented this really powerful computer that can actually calculate where that street intersection WAS at that time.

Now we can move on to several of the other big problems with time travel. (That's a REALLY BIG one we just tossed aside, but so be it for now.)

Let's tackle the old paradox problem(s). (I use the plural because there are paradox problems for both FORWARD and BACKWARD time travel, but lets stick with the BACKWARD ones for now since they are easier.)

No matter what anyone says about avoiding the classic "Kill your Grandfather" problem, there is no sound reason to trust ALL of human judgement to the possibility that at some time, some idiot will not try to do so just to see what would happen.

Since the past is now open to all of us at any time, the number of possibilities for this type of "paradox" occuring approaches infinity. In other words, it is most surely likely to occur. Actually, it would be occuring all the time, even as we speak, rendering absolutely NOTHING we now know of history to be in any way valid.

What has gone before is literally changing constantly rendering anything resembling memory a mere figment of one's imagination. But wait. We all have a great number of things we agree on that have in fact occured. (It starts getting pretty silly here doesn't it.)

In fact, one could even say that the act of traveling to the past is in ITSELF a paradox. Since the physical being that is me, most certainly was not around when the pyramids were built, for me to "travel" to a time to even witness the construction is a paradox in itself since I, in fact, was NEVER there. Nor could I EVER have been. The further one takes this likelyhood, the sillier it becomes. This also goes to the other thread on "Where are the folks from the future" that should be here now visiting us. It's really the same issue isn't it.

In all of physics, nature, what have you, there are no paradoxes. The laws of physics have never really rendered themselves to be anything but logical, eventually understandable, and in no way paradoxical.

Any which for now may appear to be a paradox, i.e. the EPR double slit problem) are only a result of our inability to fully understand what is actually happening there.

So, for me, I come to the following logic conclusion regarding time travel:

1 - All Time travel scenarios eventually lead to a paradox. (Give me any possible scenario you choose and I assure you I can find a paradox in it.) To disprove this, all you have to do is provide ONE example in which it doesn't.

2 - Physics and nature do not allow paradoxes. (Stephen Hawking has a whole treatise on this issue.) To disprove this, all you have to do is provide ONE example in which they do.


3 - Time Travel is not possible.

For me, the very idea breaks down from sheer logic alone.

I realize there will be those who will come forth with the "paradox creates a new timeline" or "parallel" universe theories, also known as 'multiverse' theory, but we can tackle that one in another exchange.

I'll leave it at the "logic" stage for now.


Although for the most part I would tend to agree with Lee in that time TRAVEL is not possible, being able to speed up time around you is known to exist, by traveling faster. That is known. As I explained in the thread "Why is this not a good explanation of time"

It should be possible to slow down time to point that time seems to stand still by slowing down. You'd have to travel in the oposite direction than the earth is traveling from the point of expansion. and since there is no such thing as a negative movement (ie.. moving backward is still a possitive movement) you can not move backward in time.

Assumeing one found the point at wich everything expands from.

This is the most logical aproch to the paradox problem, you are not really moving from one time to another.

The point in space problem since you're actually not using any point of referance except the center which is what all other objects are using to move away from.

I don't think that it is going to much longer untill they are able to deturmine at least a direction in which every thing is moving.
Ouch! This hurts my head!

Actually it wasn't so very far in our past that much of what is commonplace today was thought as impossible or magic. And since we know that it IS possible and it is NOT magic, who is to say that in 50 or 100 or even 1000 years into our future, these problems will have worked itself out.

On that note, who is to say that a traveler isn't walking among us or observing us here in our present.

Of course, even without paradoxes to worry about, time travel couldn't be done indiscriminately. The temptation alone to cash in on your future knowledge would be incredible, let alone the temptation to correct what you personally believe is wrong in the past. Truly the saving or taking of one life could have astonishing ramifications to history as we know it. Even the swatting of a mosquito could create major changes. i.e.-you kill the mosquito that harbors a disease or virus, preventing it from biting one or many people who were supposed to sicken or die. . ., what does that person do instead of lying sick in bed for a week or two? What if the person that is supposed to die, lives to have children of his own, one of which is a greater threat to civilization than Stalin or Hitler? What if that person, instead of dying meets and in an arguement that was never supposed to happen, kills the man who discovered penicillin before his discovery was made?

It boggles the mind. And because of these questions, I don't believe that time travel, if discovered, would ever be a common thing. I can't say that time travel is or is not possible because I haven't the knowledge to even contemplate such a thing, no matter that the whole subject fascinates me to no end. But if it is possible, sometime in our hazy future, it will happen. I believe that if scientists CAN do it, they WILL do it; whether or not it SHOULD be done.

The "point the universe is expanding from" is not so much a problem in determining direction. (I may have unintentionally mis-lead in using this term above.)

The problem is that there IS no real point that the universe can be said to be expanding "from". According to Cosmology, attempting to even define a hypothetical "center" for the universe is itself a flawed concept.

Galaxies of a certain age (like ours) are collapsing. The spiral arms are winding tighter toward it's center. Other newer ones are themselves expanding. But...

The Milky Way is part of the Local cluster which is itself expanding slightly. The Local cluster is part of an even greater Super cluster which is expanding more rapidly than this. The Super Cluster is moving "away" from every other super cluster in the known universe. (Overall). At a fairly equal rate IN ALL DIRECTIONS.

However, "coagulation" patterns occur and dissappear over time. The universe has patterns of unequal distribution to it's texture. The patterns change over time. When Cosmology says the Universe is "expanding", this may be true, but it is a gross oversimplification in terminology of what the process is.

In a way, ANY point that would be definable within it COULD be said to be the center. Or in other words, there isn't one. There is no place that can be defined as one edge that is opposite an opposing edge. Hence, no definable center. But even that is a simplification. Since space AND time began at the big bang, any point in the universe can be said to be equally infinite in distance from any hypothetical "edge" since all we can concieve of is contained within this infinity. The very words begin to become inadequate for accurate description. We're stuck with flawed conceptualization for now. (No MY head is starting to hurt!)

I do agree with you that speed does not constitute time travel. Just Time dilation. And even that is only relative for the objects you are comparing the velocity variance for. i.e. In the Twins "paradox", the traveler ages slower. But it's NEVER measurable unless he returns to the original point of reference, or at least uses some external reference point to compare it to. If he only ever traveled AWAY at high speed, who can say for sure just which one is traveling "away" from the other. This is the classic TWO body problem. The effect may indeed be very real, and measured by experimentation. But if you NEVER returned, how would you EVER prove just how much less you had aged by being gone. Universal center, time dilation, etc., all boil down to "Compared to what?"

It's why I like to use the example of the traveler staying within sight of the one who does not. At least they can agree on the fact that they both observe the earth make the same number of revolutions around the Sun. It's the traveler's biological clock that slows down. Like the mechanism of any clock he takes with him. But only when he actually returns to the original point of departure is the difference actually measurable. Both would count 50 revolutions of the Earth (for example), but the traveler would have aged lass in the same number of revolutions. For the traveler, a revolution of the earth around the Sun DOES NOT constitute a "year" of his biological time. Cute huh! But's it's been measured and proven to be this way. No "time travel" involved in any of this.


I very much agree with your point about what we take for granted now, that we used to think was impossible.

Truth is, I sincerely HOPE I am wrong about time travel not being possible. For sure there are many things we have not thought of as yet, or even conceived of.

All I know is that for me, the "classic" time machine concept, or using a so called worm hole to travel "forward" or "backward" in time is a concept of time travel that just doesn't wash for me as even logical.

For me there are two simple conditions that we tend to overlook which are right in front of us at all times, and so painfully obvious, we ignore them and try to look past them.

1. The past has already happened. It's over. It no longer exists. Anywhere, anywhen.

2. The future hasn't happened yet. It doesn't exist anywhere, anywhen. Although we are constantly traveling to it every instant just by being alive.

In the classic sense, there is no "past" or "future" to "travel" to.


Hi Lee,

I need some clification on your statements:

"In all physics, there are no paradoxes...they are are only the result of our inability to fully understand what is actually happening out there."
"Give me any possible scenario you choose and I and I assure you I can find a paradox in it."

Sure Jim... I'll try anyway.

To the first:

I know of no instances where Physics or Quantum Mechanics has declared anything they have discovered, that has come to be current accepted theory, in which a paradox is accepted as part of the known laws, or even referred to as such.

Save ONE possibility known as the EPR paradox which is a rather old one in fact that goes all the way back to the double slit experiment. It is at the core of the argument where Relativity and QM actually DO NOT reconcile with each other. QM puts it as the cause for collapsing wave theory since it gives the appearance of one event being the cause of another at EXACTLY the same instant, even if it were a light year away. Einstein NEVER bought into it calling it a "spooky force at a distance". It is not so much a real paradox as it is merely called that because of the as yet irreconcilable inconsistency it suggests in relativity. I see it as a result of the Heisenberg uncertainty principle, and do believe it can be reconciled at some time in the near future. So do several Quantum Physicists. In fact there are several theories on the table that could reconcile the issue.
A true paradox is one that would by it's nature be irreconcilable. The classic "immovable" object being struck by the hypothetical "unstoppable" force. A good example of an IMAGINED paradox. But since there are no immovable objects or unstoppable forces in the laws of physices, it's just an exercise in conception only. So...
What possible paradoxes could there be in physics or the laws of the universe? I know of none. Do you know of any?

To the second:

This refers to any depiction of "time travel" in what we refer to in the classic sense. (Someone travels to the past or to the future.) How (time machine, worm holes)would be irrelevant. Any description of this occurance that I've ever heard of, always leads to some paradox I can think of. In fact, I would have a hard time trying to define a scenario of time travel that DOESN'T lead to one.

Dr. Stephen Hawking has a hypothesis that the laws of the universe must contain some as yet undiscovered "safety mechanism" that would prevent time travel from ever occurring since by nature, it HAS to lead to a paradox. Dr. Hawking also states that there are no paradoxes.

It's been a while since I've read "A Brief History of Time", but I THINK it's near the end of THAT book somewhere that he says this. I could be wrong and it may be a later paper. He also re-iterated the point on the Time Travel special on PBS several months ago.

I do believe Dr. Hawking is one of the most logical thinkers of our time. Given his handicap, he certainly has a much longer time to think about ever word he writes than most of us take the opportunity to. We could all probably learn a bit of THIS from him.

Hope this clarifies and thanx for asking.


An interesting piece of work indeed. It seems that Andemicael and I are in agreement when he says:

"(Note: relativistic "time dilation" effects do not in any way affect the steady, normal flow of <subjective> time)."

I've said essentially the same thing a few times here, although I aknowledge some folks do refer to it as "Time travel". The more you examine the characteristics however, the more you realize it is not.

He also states:

"...As we know, physical reality exists in its totality, in a block-like fashion, with all spacetime points existing in an "all-at-once," concurrent manner; there are no before/after, earlier/later relations to consider in this context. And the word "history," here, simply describes a "frozen" and concurrent group of points."

and then:

"...We must remember that it is "temporal history," and not "physical history" which "recedes dynamically into an inaccessible past." Temporal history--i.e., "the temporal sequence of experiences"--must certainly remain fixed forever; but physical history itself can certainly be manipulated."

...which to me is his way of saying you can't go back to the past (which I agree with), but the very acts one engages in "in the now" affect all of physical history yet to come. Your REMEMBERANCE of past events is the temporal, while your PERSISTENCE in the "now" is the physical. Again, agreed.

But one thing he says:

"I have argued in other essays that temporal conflicts or inconsistencies cannot arise between two experiences of reality."

...(which I would also have to concur with), is followed by this:

"I believe this conclusion has implications for time travel: it seems to suggest that self-consistent, geometric "time travel" scenarios are possible."

...which evades me completely. I cannot see how the two are related unless he is implying it in a merely temporal sense (as HE defines "temporal").

If he is suggesting PHYSICAL time travel is possible because the temporal memory experiences of two individuals can never create a conflict, he's lost me here. I would need further clarification.

How do you see this?


Again, agreed.
Guys , Guys you are not going to take the 1st trip 1 million year back in time or a million years ahead. Baby steps is the only way to map out the time stream. Your point of referance is going to be your now when ever that is and where ever that is. When you start out on your 1st. trip though time you will only travel one or two seconds backward in time
No one can be sure that time has always moved at the same speed. Yesterdays time could of moved slower then todays time. This would be more of a problem then your point of reference.
There must be a point in which time where time started and for that matter there must be a time where time ends. These 2 points would also be reference points, But more important if you could get to the point in time just after the start of time then would you be traveling the same speed? Would you be able to phase in or out of that time?