I receive emails daily from many people, scientists and laymen. About half of them are sympathetic. The others take strong issue with my views on spacetime and time travel. Most of my critics seem to be recent physics graduates and undergraduates, although a small percentage are physics teachers and retired physicists. About a third of my detractors are righteously offended: "How dare you call professional physicists crackpots?" They then go on to call me worse names.
The others fall into two main groups. The first group is adamant that motion in spacetime is possible. The second group readily accepts that nothing can move in spacetime but is nevertheless convinced that a changeless spacetime does not preclude the possibility of time travel. Note that the existence of at least two mutually contradicting factions within the physics community does not add to its overall credibility in this matter, especially when the matter in question has to do with something as crucial as the nature of motion and time!
What follows are some of the more common objections and my rebuttals. I will add to this page from time to time as I receive more criticisms in the mail. Please read the main page first.
This argument is a favorite of misguided relativists, Nobel prize winners among them. I agree that processes run slower under gravity. I just disagree with the interpretation. Relativists claim that clocks run slower because time dilates. This is like saying that unemployment is up because the unemployment rate is up. Sometimes I find myself wondering whether the field of relativity physics has been taken over by charlatans masquerading as scientists. Time does not dilate for the simple reason that time, by definition, cannot change. The slowing of clocks is more likely due to energy conservation principles that come into play when a huge number of particles are interacting locally.
But let's put that aside for a moment and assume that a clock or some other body has a time coordinate that can change in a certain direction. Let's take the extreme view of a clock that is moving at the speed of light with respect to us. According to relativity, the clock completely stops. The question that immediately comes to mind is this: if the clock had traveled in time relative to us, why is the clock still visible? If it had really slowed in some time dimension that we all share, it would simply disappear from view.
Time dilation is an unfortunate misnomer, in my opinion, because it gives the impression of an independent time variable (an oxymoron) that causes things or processes to slow down. Again, clocks run slower, not because time dilates, but because their internal processes slow down due to energy conservation principles. "Time dilation" = process slowdown. There is no causal link between the two. They are equivalent.
The problem is with the use of the expression "time dilation". If the framers of relativity had understood that time is unchanging and abstract, they would have never used it. Time is neither relative nor can it change. One can indeed talk of a fundamental yet abstract time interval, one which is fixed and absolute. Since it is abstract, this fundamental interval must be derived from a fundamental length and speed. But that is a subject for a future article.
This is a common misconception. It is prevalent mostly among mathematicians who are prone to equate math with physics. It may be "ok" in calculus to use any arbitrary variable to parameterize "change", but not in physics. Note that I put "ok" and "change" in quotes because I think it's a bad practice that leads to all sorts of misunderstandings. Math is a unitless system. For example, the coordinates of a point are just numbers. Nothing in the system identifies its physical relevance. The axes could represent anything from temperature to distance to loudness. Asserting that one coordinate is a function of another does not express change or motion. It assumes the a priori existence of change and describes how the evolution (another word for change) of one coordinate is related to or dependent upon the evolution of another.
One of the lessons one learns in physics is the importance of units of measurements. Time is measured in seconds and distance is measured in meters for a reason. The reason has to do with their identity or meaning. It is also important to note that, in physics, motion is not defined as a function of an independent variable called time. On the contrary, it is time that is a dependent function of motion/change. Motion/change is observed and a time interval is abstractly derived. Time itself is never observed; it is abstract. The derivation of time from motion is precisely given: the faster the change, the smaller the interval. It is for this reason that time is the denominator in the equation of velocity. The derived interval can be calibrated and serve as a parameter with which to compare the rate of change of one phenomenon to that of another.
There is only one valid evolution parameter in physics: time. Time is a dependent parameter and is expressed in seconds so as to distinguish it from other variables. If a parameter is not measured in seconds, it is not parameterizing any sort of change or motion. The definition of change/motion is a very rigorous one and must not be tampered with so as to fit crackpot ideas like time travel.
First of all, my site is directed at the
lay public (who pays for
scientific research and expects to get good science for its money). The only
time that is relevant to the lay public is historical time (i.e., tau
or proper time in physics terminology). In the context of time travel this is the only time that
matters. tau is an invariant evolution
parameter that is used in physics as a calculational tool with which to describe a rate of motion or change.
Since tau is invariant, any talk of time travel is crackpottery.
Third, there is indeed an evolution at c in the fourth dimension (from which we get the light cone) but, like all evolutions, it is a spatial evolution. Moving in any direction in the fourth dimension of 4-space (not spacetime) does not constitute time travel. If one could move in the opposite direction, one would not be traveling backward in time to the past as the pundits would have it. One certainly would not find one's great grandmother going about her business.
In conclusion, to speak of time-like paths is sheer crackpottery.
This is, by far, the most common argument for time travel. It comes from laymen and physicists alike. In my opinion, it is the easiest one of all to demolish, and yet, some people never seem to get it. Others understand it immediately and still others have to think about it for a long time before they do.
First of all, dt/dt does not mean 1 second per second. The units cancel out. This fact alone destroys the argument and there really is no need to go further. However, I feel it is important to emphasize the following fact regardless of how shocking or implausible it may be to some:
The commonly held notion that time changes is as fallacious as it is detrimental to our understanding of motion. Why? Because "time changes" is a self-referential statement. It is hopelessly illogical! We never observe time changing. We observe changes in physical processes from which we derive static time intervals. We then use these static intervals to quantify the rate of change of various other processes.
I think it is important for the reader to understand the difference between the word change as used (by some) in calculus and change as it is used in physics. A change in calculus is the difference between two numbers. dx, for example, is the vector difference between two positions. dx simply represents distance. Likewise dt is the difference between two measured times, i.e., an interval.
A change in physics is something else altogether. It is an event or phenomenon that is conventionally expressed with the use of the evolution parameter t (time). Examples of change in physics are motion (a change in position) and acceleration (a change in velocity). The decay of a subatomic particle is also a change.
Whenever there is motion (a change in position) there is also velocity. In physics we express the rate of motion with the expression dx/dt, not just dx. dx by itself does not represent a change in position but is a static measure of length or distance. Likewise, dt is not a change in time but a static measure of some interval. To emphasize, it is the combination dx/dt that describes a change of position in physics, not dx by itself or dt by itself.
In my opinion, a lot of it has to do with peer review and the political climate within the physics community. No physics author can get published unless he or she is approved by their peers. Authors therefore try to write papers that agree with the prevalent views of the more famous physicists. Political correctness is alive and well in science just as everywhere else. Relativists have claimed for close to a century that they know the cause of gravity and that it has to do with the metrics of curved spacetime. Thus anybody who argues that there are no such things as spacetime or a time dimension in nature, will either be branded as a crackpot or given little exposure. And if famous physicists like Thorne, Wheeler and Hawking say that time travel is possible in principle, who is brave or powerful enough to contradict them?
And those who do not like to see the state meddling in scientific matters should remember the sizeable chauvinism of science: for most scientists the slogan 'freedom for science' means the freedom to indoctrinate not only those who have joined them, but the rest of society as well.
As I mention elsewhere on this site, I first learned that nothing can move in spacetime from a relativity professor who teaches at Elizabethtown college in Pennsylvania. There are a lot of relativists who know and understand that spacetime is an abstract math construct with no counterpart in nature. They know that nothing can move in spacetime. Self preservation, however, is sometimes more important than truth. Publicly disagreeing with heavy hitters like Hawking, Wheeler and Thorne is not a good way to advance one's career. Some, like Dr. John Baez, may think it is more prudent to advance absurd notions such as the existence of an infinite number of nows than to reject the concept of a time axis altogether. I suspect also that one reason has to do with people wanting to protect the reputation and dignity of their profession. It's almost like a religion to them: we are right and the others are wrong and that is that.
As to why famous physicists like Stephen Hawking or Kip Thorne have not figured out that time travel is pure crackpottery or something as simple as the impossibility of a time dimension, I have no idea. I guess somebody will have to ask them the question and see what they have say. I encourage my readers to write to them and ask them if they so desire. You can find their email addresses on their respective sites.
I would not be surprised to hear, despite all that they have written on the subject, that they suddenly claim that they have suspected or have known these things from the beginning. My bet is that they will insist that they have been misunderstood and/or that I am a crackpot who should not be taken seriously. Do not underestimate the capacity of human nature for deception and cowardice. This is the reason that I say to my readers, please do not take my word for any of this stuff. Figure it out for yourselves.
In conclusion I find this quote from Paul Feyerabend, one of last century's most famous philosophers of science, to be quite inspiring:
A candid look at Stephen Hawking can be found here: The Hawking of Stephen Hawking.
©2004-2006 Louis Savain
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