TIMETRAVEL PHILOSOPHY
If a human on Earth (or through the Hubble telescope, because of its
relatively low orbit) gazes into space, he looks into the past. A glance at the
Sun shows it as it was eight minutes ago. On the edge of the observable
universe, one sees object who have been there at least 13.8 billion years ago.
Observing far away objects is not time traveling. If it were, that would
mean that our line of sight would be a moving object. We only collect light
that reached us from that distance and so this light (and other wavelengths of
electromagnetic emissions) is what travelled the distance.
If we want to observe a far object as it really is, we will have to go
there. Let us imagine that we go on board a space vessel which can reach nearly
the speed of light, let’s say 99,99% c (for further ease
of use: c- [c superscript
minus]). This is a thought experiment because: Motion at nearly light speed is
impossible according to Einstein’s theories and: As no scientist has yet
falsified them (apparently because these theories are so solid) the
impossibility to travel at nearly the speed of light is a commonly accepted
fact.
In this thought experiment, numbers will be rounded; if necessary, I will
use 300,000 km/s as the speed of light and 2.5 billion light years as the
distance to the Andromeda galaxy. I will also use abbreviations like
‘Andromeda’ for ‘the Andromeda galaxy’. In the original (not published) Dutch
version of this essay, I also used English concepts in stead of less popular
Dutch words; the street language of astrophysics.
We find ourselves on board the spaceprobe ‘Vaiana’[i]. Starting off with a
short Earth orbit – where time continues in the same old pace whilst we undergo
time dilation, although still unfelt. After a few more orbits, we head for
Jupiter for a gravity slingshot, and the same procedure will be performed
around Saturn. Both were together with Earth in a equilateral triangle around
the Sun (least preferable), and thus the trip from departure around both
planets took a few years, but compared to the entire trip we are making, it
hardly makes a difference; this extra time is like “a spec of dust in the
vastness of spacetime”. Eventually we gain an enormous acceleration from a
passage by the Sun. Via a number of other passages by big stars in the Milky
Way, after some 1,000 years we finally leave our home galaxy at c-.
2.5 million years later we fly between the stars of Andromeda. What we had
ever seen from Earth, was 2.5 million years old. Now, 5 million years from that
moment have passed: the time for Andromeda’s light to reach Earth and 2,5
million years to get to Andromeda.
At least some footnotes apply to this scenario. First, no human or other
living creature would possibly survive such a trip, perhaps only numerous
generations of a species. Humankind has not even thrived one-tenth of that time
here on Earth. What favorable developments will the humans on board Vaiana miss
out? What are the unfavorable effects of lack of gravity and all sorts of
radiation have on humans and space ship during 2.5 million years? And so on.
Then, there is the effect of time; several effects in fact.
Vaiana is heading for Andromeda. It left in the present, the ‘now’
somewhere in what we now consider a possible future. At the end of the journey,
in the perception of everyone staying behind at home, the Vaiana crew will
experience ‘later’. For the crew it is also ‘later’, but their perception of
‘later’ will come sooner because their time runs slower. A question that can be
asked here is: how wil the time delay develop as speed increases towards c-,
linear or exponential? How big is the exponent? Let us assume that at c- time
dilation is 90%, than the mission arrives at Andromeda in approximately 250,000
years. In the perception of Earth that would still be 2.5 million years.
Perhaps by acceleration to c- the space in
front of the vessel is warped towards it, while space at the rear is warped and
pushed away.
Another time effect is, that the Vaiana party take their own ‘now’ on board
with them. What they leave behind is a ‘later’ (a future that will never
unfold) and the destination is a ‘former’, the past. Anything observable from
the vessel in the forward direction has already been, has passed, is past. But
as Andromeda gets closer in range, this past gradually changes into a ‘now’.
What the party has left behind, was a possible future, but instantly became
past without that future. This leads to conclude, that the party and the vessel
carry a ‘now’-bubble in and around them, and the wake becomes a past and what
lies ahead gradually shifts from past to present.
In my personal (humble) opinion, no such thing as ‘future’ can ever exist,
other than in speculation. Even contractual arrangements, e.g. with the goal to
receive a capital after periodic payments of a premium, which as such predict
the payment of that capital, remain speculative. The reason is that there’s
always the possibility of unforeseen (unhoped, unexpected) events. A person
with specific perspectives, like receiving a capital of becoming a grandparent,
may just have been raided by a lethal blaze on 9/11/2001 as two airplanes
entered the Twin Towers, unpredictedly; the all of a sudden the combinations of
insured plus capital or granddad plus grandchild no longer exist.
Future is only a figment of imagination in the brain or organisms like
humans, who can draw abstract pictures of things that have not yet occurred. No
‘intelligent’ animal (e.g. a dog) can do likewise; a dog can imagine a walk as
his boss picks up the leash, but that is merely instinct or some kind of
intuition and is not the same as a notion of consequences from its own
behavior.
Can you imagine a bubble of ‘now’ racing through spacetime at c-?
What do you think of the concept of ‘future’? What ideas do you have about
timetravel? Please do not hesitate to send your comments; if in my humble
opinion they are worth publishing, I will do so. And of course, I very much
appreciate if experts on these subjects submit their views. Would you then
please add your own brief ‘about me’?
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