Time and space travel

[Nigel_Strange]

If you imagine that time is a dimension, like space, then you can imagine a timeline going back to the origin of the universe (presumably, a Big Bang).

It is generally accepted that space is, over time, expanding. Distances between stars and between planets is growing.

So, one possible mechanism for space travel would be to go back in time to a point at which two currently distant points in space are adjacent to one another, then move into the adjacent space, then move forward in time until present. In this way, you should be able to go anywhere in the universe, provided that you can travel backward and forward in time.

So, if you believe in time (which I don't) then this would be a mechanism for the fabled "jump drive."

[CS-ACI-]

Hello,

Deep.

Steve

[Rubber Chicken]

But... If Point A is your current position, point B is your destination, and point C is where Point B was a billion years ago... Wouldn't moving back in time to Point C then forward to the present leave you at Point D - the place where Point C presently exists but no longer overlaps with Point B?

[Marvin]

The software program for such a move has already been written ... but there is, as of yet, no computer capable of running the program.

[DaveK]

The ongoing expansion of spacetime happens only at long (inter-galactic cluster) distances - it's not measurable between stars or even between galaxies in a cluster

If you went back in time in Sol then If you flew to another galaxy in another cluster - no mean feat since intergalactic distance have been enormous ever since the galaxies formed - which was quite some time after the big bang it would still take an enormous amount of time. The other galactic cluster might be closer to Sol than it was when you set off - but it might not because the galaxies in clusters and the clusters themselves are moving all the time. Some distant galaxies have blue shifts - they're moving towards us. At short - interstellar or inter planetary distances the expansion of space time is tiny so, for example, the distance between Sol and Alpha C depends more on their individual orbits around the galactic centre than on what the expansion of spacetime has done

Neat idea though!

Worm holes are still your best bet - artificial or engineered

[Marvin]

If all the matter in existence was created with the big bang and you went back in time to that instant ... wouldn't your mass supersaturate the universe?

[DaveK]

Matter didn't separate out until the universe had expanded sufficiently and until it had cooled sufficiently for matter to exist (protons, neutrons and electron in a photon rich plasma) and cooled further until electrons could actually link with protons and neutrons to form atoms. According to the theory, the light elements (hydrogen, helium, and lithium) were produced during the first few minutes. Briefly this is our best idea of the first few minutes;

Immediately after the Big Bang the universe was tremendously hot as a result of particles of both matter and antimatter rushing apart in all directions. As it began to cool, at around 10^-43 seconds after creation, there existed an almost equal yet amount of matter and antimatter with a small bias in favor of matter. As these two materials are created together, they collide and destroy one another creating pure energy. As a direct result of an excess of about one part per billion, the universe was able to develop in a way favorable for matter to persist. As the universe first began to expand, this discrepancy grew larger. The particles which began to dominate were those of matter.

As the universe expanded further, and thus cooled, common particles began to form. These particles are called baryons and include photons, neutrinos, electrons and quarks would become the building blocks of matter and life as we know it. During the this period there were no recognizable heavy particles such as protons or neutrons because of the still intense heat. At this moment, there was only a quark soup.

As the universe began to cool and expand even more, we begin to understand more clearly what exactly happened.

After the universe had cooled to about 3000 billion degrees Kelvin, a major transition began which has been likened to the phase transition of water turning to ice. Composite particles such as protons and neutrons, called hadrons, became the common state of matter after this transition. Still, no matter more complex could form at these temperatures. Although lighter particles, called leptons, also existed, they couldn't react with the hadrons to form more complex states of matter. The expansion continued, the universe cooling as it did so. The leptons, which include electrons, neutrinos and photons, were able to join with the hadrons to create what we would recognise are normal 'matter'.

After about one to three minutes had passed since the creation of the universe in the big bang, protons and neutrons began to react with each other to form deuterium, an isotope of hydrogen. Deuterium, or heavy hydrogen, soon collected another neutron to form tritium. Rapidly following this reaction was the addition of another proton which produced a helium nucleus. Scientists believe that there was one helium nucleus for every ten protons within the first three minutes of the universe. After further cooling, these excess protons would be able to capture an electron to create common hydrogen. Consequently, the universe today is observed to contain one helium atom for every ten or eleven atoms of hydrogen. These two are still the overwhelming matter in the universe.

To summarise; during the first three minutes after the Big Bang, the universe cooled from 10^32 K to 10^9 K. After this cooling took place, protons and neutrons that formed soon after the Big Bang collided to produce hydrogen and helium mainly. By the time matter fell out of the super hot photon mix there was room for it. Expansion continued, leading to a (nearly) smooth distribution of matter. Gravity caused patches to condense leading to galaxies and stars and planets etc. And the rest, as they say, is history!

An excellent read for the educated layman is The First Three Minutes by Stephen Weinberg (Nobel Prize Physicist who worked on the big bang)

An awful lot happened in the first fractions of a second. Most of the stuff that lead to the universe as we know and love it, took place in that first three minutes

[Marvin]

As the universe began to cool and expand even more, we begin to understand more clearly what exactly happened.

That's news to me ... I didn't even realize we were around that far back.

[DaveK]

'begin' not 'began'

[PaulB]

The ongoing expansion of spacetime happens only at long (inter-galactic cluster) distances - it's not measurable between stars or even between galaxies in a cluster

If you went back in time in Sol then If you flew to another galaxy in another cluster - no mean feat since intergalactic distance have been enormous ever since the galaxies formed - which was quite some time after the big bang it would still take an enormous amount of time. The other galactic cluster might be closer to Sol than it was when you set off - but it might not because the galaxies in clusters and the clusters themselves are moving all the time. Some distant galaxies have blue shifts - they're moving towards us. At short - interstellar or inter planetary distances the expansion of space time is tiny so, for example, the distance between Sol and Alpha C depends more on their individual orbits around the galactic centre than on what the expansion of spacetime has done

Neat idea though!

Worm holes are still your best bet - artificial or engineered

I think if you google the mooon moving away from earth you wil find there is evidence that it is occurring.
I believe one of the methods they use as proof of expansion is the change in doppler shift in the light spectrum of stars and galaxies.

[DaveK]

I think if you google the mooon moving away from earth you wil find there is evidence that it is occurring.
I believe one of the methods they use as proof of expansion is the change in doppler shift in the light spectrum of stars and galaxies.

Yep the Moon is moving, but that's because the Moon really is moving not because the space between the Earth and the Moon is expanding.

Yep the redshift of distant galaxies and clusters does demonstrate that the distance between them and us is changing - but for two different reasons:

1: the far far away galaxies and clusters are red shifting because space is expanding. This is a primary 'proof' of the big bang. But we are so far away and space is expanding so much we can tell how they are moving relative to us just that the expansion of space is increasing the distance. They may in fact be moving in our direct, but just not as fast as the expansion of space is increasing the distance from us - like hopping on an upwards escalator, getting half way and changing your mind - you can head down but if the escalator heads up faster you actually go up!!

2: the closer galaxies, like the ones in our cluster show tiny red and blue shifts depending on whether they are moving towards us or away - not because of the expansion of space but because they're moving through space - like the planets and asteroids moving in their orbits. An Andromeda – Milky Way galactic collision is predicted to occur in about 4 billion years between what are the two largest galaxies in the 'Local Group'. Should be spactacular if you watch a time lapse taken over a couple of hundred million years! (There are sims on the web)

Just keep in mind that the relative movements of galaxies/stars/planets/moons etc can be due to the expansion of space (long range) or the actual movement of the bodies through space (short range)

[Nigel_Strange]

Is it possible to distinguish between space expanding between two bodies and them moving apart? It would seem to me that the two events would have the exact same behavior, and in a way, I can't really imagine any meaningful differentiation.

Also, I'm not certain that time exists. We measure what we call time by comparing the movement of things against the movement of other things, but the "thing" called "time" does not actually get directly measured. I think it's made up.

[Edited on 12-20-2014 by Nigel_Strange]

[DaveK]

As I understand it the 'metric expansion of space' (as it is poshly called) is a scientific theory according to which there is an increase of the distance between two distant parts of the universe with time. It is an intrinsic expansion where the scale of space itself changes and it is a generic property of the universe. This is different from other examples of expansions and explosions in that, as far as observations can tell, it is a property of the entirety of the universe rather than a phenomenon that can be contained and observed from the outside.

The model is valid only on large scales (roughly the scale of galaxy clusters and above). At smaller scales matter has become bound together gravity and such things do not expand at the metric expansion rate as the universe ages. Calculations suggest that only galaxies receding from one another as a result of metric expansion are those separated by distances larger than the distances associated with the gravitational collapse that are possible given the matter density and average expansion rate - the gravitational attraction between galaxy clusters far enough apart is slower than the expansion of space. To use the escalator analogy, when you're trying to run down an up escalator, the further from the bottom you are the faster the escalator is moving you away. (or the slower you can run down)

A really intriguing thing is that Einstein's relativity that puts an upper speed limit (speed of light) only applies to objects that are (poshly) in 'causal contact' with each other. This translates out as 'the only objects not in causal contact are those for which there is no event in the history of the universe that could have sent a beam of light to both. For example, if the universe was not expanding and had existed for 10 billion years, anything more than 20 billion light-years away from the Earth would not be in causal contact with it. Anything less than 20 billion light-years away would be in contact because an event occurring 10 billion years in the past that was 10 billion light-years away from both the earth and the object under question could have affected both. Objects beyond this limit are not limited to the speed of light when measured relative to us. Calculations show that a galaxies more than approximately 4.5 gigaparsecs away from us are expanding away from us faster than light. The over all result is that although the big bang occurred about 13 billion years ago the region visible from Earth (the observable universe) is a sphere with a radius of about 46 billion light years, based on where the expansion of space has taken the most distant objects observed. The size of the Universe is unknown; it may be infinite and there are parts of the universe that we will never see because their light can't reach us.

As for the existence of time . . . it's been challenging philosophers and scientists for millennia. It's a wonderful mind boggler. Quantum theory suggest that time is quantised - its 'tick' (the plank time) is 10^-43 seconds or perhaps that this is simply the smallest time interval that can be measured (like absolute zero is the lowest temperature and the speed of light is the faster speed). But Relativity shows that two observers viewing the same event can both show that they saw it before the other observer!

But if time doesn't exist then what is it that gives us the perception of the past, present and future - the famous 'arrow of time'?. And what does Dr Who travel through? And if we've just made it up what would the universe be like if humans had never appeared? It's a more complex version of the 'tree falling in an empty forest making a sound' puzzle. Could there be a future and a past in a human free universe? And take human to = any life intelligent to ponder about time! And if time if imaginary, what is it that clocks are measuring?

Things like this are (partly) why I love science - scientist by nature, scientist by choice, scientist by training! And now I'm retired I have time to study it again - I'm part way through a college level course in cosmology. I can recommend 'The Great Courses' to everyone (they cover everything - maths - music - economics - science - philosophy - history - sociology - religion - literature - art - business/economics/management/leadership skills and - as they say - much, much more!)

[Nigel_Strange]

Thanks for your excellent lecture, Professor DaveK. I really enjoyed reading your post.

As for what the universe would look like without humans, I would venture it would look the same. If we invented time as a concept, it does not mean that our invention changed the structure of the universe in any meaningful way.

As for the tree in the forest, it makes a loud crash.

Here is my reasoning: there is no tree. The "tree" is a hypothetical construct of my imagination. If I imagine a tree falling in the forest, then I am observing the imaginary representation of the tree, and in my imagination, that tree makes a loud crash.

[DaveK]

Well Grasshopper, your journey progresses!

[Marvin]

As for if a tree makes a sound in the forest: according to Wikipedia, yes and no.

In physics, sound is a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a medium such as air or water.

So, yes.

In physiology and psychology, sound is the reception of such waves and their perception by the brain.

So, no.

[Nigel_Strange]

There is no tree. The tree is imaginary.

See, the whole thing is a construction of words, not of real things. Thus, we imagine the tree falling in an imaginary forest. In the imaginary forest, you are observing the imaginary tree.

The problem is not with mechanics, but with language. We believe that language constructs a reality, but it's really just language.

[DaveK]

If the sequence Marvin describes is true then time exists even without humans since the statement that sound is a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a medium such as air or water infers a sequence of events that follow each other in . . . . time

If there is no tree then logically there is no person to imagine it and if there is no person there is no-one to imagine time. Followers of Nihilism and solipsism - you might have been right all along!

And finally - I've always believed that language describes reality rather than constructing it. I can use language to describe a flying elephant (well Disney did!) but in this case language neither constructs the elephant nor does it describe an aspect of reality - only an idea in someone's imagination. Which leads me to ask - is an idea real? Or is it only imaginary?

[Nigel_Strange]

Sorry: missing the point I'm afraid. The tree that is falling in the forest with nobody around to hear is the one that does not exist. It exists as a word problem, not as an actual tree. That's why it's imaginary, and that's why I imagine it to make noise (imaginary noise). The problem here, and with most problems, is that our way of conceptualizing the problem is language-based. Language makes it easier to communicate abstract ideas, but it also hobbles our ability to think outside of the linguistic rules that we have agreed on. That is people are having so much difficulty seeing the point that I'm trying to make here.

To find if the tree actually makes sound, you must observe it. Only direct evidence can solve the mystery of whether the tree makes sound. However, if you postulate that you cannot observe the tree, but must imagine the tree instead then we are dealing with an imaginary tree, and we are left with imaginary sounds, as we imagine the tree falling in an imaginary forest. That imaginary tree makes an imaginary crash, at least in my imagination, and if it doesn't do the same in your imagination, it's pointless to argue, because we comparing imaginary trees, and not real trees. It is like two kids arguing about whether Batman or Superman would win a fight. Each kid imagines the battle separately, and each kid comes up with a separate answer. The fact that neither Batman nor Superman are real is beside the point.

The problem with time is that it is so wrapped up in our language that it is impossible for us to describe a sequence of events without describing them in time. Our language is heavily time-biased.

However, when you are measuring "time" what you are measuring is the movement of things, not time itself. You are comparing whether someone gets to the end of a race before another person. Or you are comparing whether a space-ship gets to a designated point in space before the hour hand of a clock gets to the 3, or before the cesium crystal vibrates 2x23 times, or before the planet aligns with another planet.

There is an order of events that happen, but the concept of time is just a way for us to describe that order. We think of time as a line, and we draw events on that line, and we use that to make sense of the world, but to reify the concept of time just because it makes things easier to work with is a linguistic contrivance, not necessarily an accurate model of reality.

Suppose we are moving away from one another at the speed of light (or near it). You might be able to locally disrupt the normal order of things, as for instance, the second hand of my clock moving near the speed of light might reach the 12 later than the second hand of your clock, which is "still." However, to me, you are moving away from me at the speed of light, while I'm standing still. The one of us that is moving depends on the frame of reference. Whose frame are we talking about? The thing is, we cannot compare notes because we are too far away for information to be communicated...

Unless we use a Tangler. Now THAT would be an interesting experiment.


[Edited on 12-22-2014 by Nigel_Strange]

[DaveK]

So when you close your eyes everything ceases to exist?

Measuring time by a movement doesn't mean that time doesn't exist. All measuring is relative to something else. Temperature (which is the perceived effect of the average kinetic energy of the atoms/molecules in a substance) can be measured by looking at the expansion of a solid or a liquid (mercury thermometer or a metal coil thermometer) or measuring the intensity of IR light the object emits by turning it into an electrical signal that can move a dial pointer or control a digital display. That doesn't mean that temperature is imaginary or that atoms don't exist

The problem with time is that it is so wrapped up in our language that it is impossible for us to describe a sequence of events without describing them in time. Our language is heavily time-biased. But surely that's because time exists and is of central importance to us and to the universe. We are born, we live, we die, the Earth turns on it's axis every 24 hours and it travels round the Sun in a year. None of that can happen if time is just a mental construct. Worms are born, live and die - again a journey through time, but I doubt that they have a mental construct of 'imagined' time

To find if the tree actually makes sound, you must observe it. Only direct evidence can solve the mystery of whether the tree makes sound. Would unthinking observers like a microphone do?

However, if you postulate that you cannot observe the tree, but must imagine the tree instead then we are dealing with an imaginary tree, Slippery language and dodgy logic. There is a tree in my garden. I'm on holiday elsewhere. I cannot see the tree. I can remember the tree - how it looks, where it is. I might imagine the tree bending in the wind when I hear a weather report about gales back home. That doesn't make the tree imaginary. It's still there, in my still existing garden, waving in the real blowing wind. 'Nimloth the Fair' (The first White Tree of Numenor) is imaginary, created in the imagination of Tolkien. The tree is my garden is real and I may come home to face a fence replacement bill if it falls and damages (silently or not) the fence between me and my neighbour.

So an imaginary tree might or might not make an imaginary sound depending on whose imagining it. But a real tree in the Amazon forest, regardless of whether there's any one (or any suitably evolved creature) present would make a sound (as defined by Marvin above) if it fell. The only stumbling point is whether you accept sound as the physical cause (pressure waves in a medium) as well as the mental perception in a brain caused by those waves in your ear. As Newton said . . . 'the rays are not coloured' - colour only exists in a mind caused by the frequency of emr photons hitting your retina and being converted to nerve signals.

And the difference between before it fell and after it had fallen would be due to the passage of (real) time.

Or we can agree to disagree

[Marvin]

So when you close your eyes everything ceases to exist?:)

Yes. But it works much better if, instead, you use a towel to cover your eyes.

Btw, if you put that tree into a box with the cat, then you can ask, "Has the cat climbed the tree?"

[Marvin]

The question then becomes, "Is this the cat?"


Schrödinger's cat



Or, "Is this the cat?"

[Nigel_Strange]

No, sorry...still missing the point. I am afraid that no matter how I try to explain this, the idea is still not getting through. This is going to take a long post. I'm sorry in advance. I hope this works.

You can imagine a real thing. You can imagine the tree in your garden...but that representation of the tree in your garden that is currently in your imagination is not the same thing as the actual tree in your actual garden. You have a mental representation of a real tree. If you imagine your tree in your garden falling down, it is not the same thing as the actual tree actually falling down. Does that make sense? You see the difference between a mental representation of a thing and a real thing?

You can also imagine the tree of Numenor, but that representation does not have a referent.

The whole word problem about a tree falling down with nobody around to hear it is an imaginary problem. The problem does not exist in reality. It only exists as an imaginary problem, with an imaginary tree in an imaginary forest. It is a word problem, not a real problem.

In the real world, if a tree falls down in the Amazon, which happens all the time, and nobody is there to record it, then so what? Nobody heard it. It does not mean that it did not make air vibrations. I never said that. What I am saying is that if you try to escape the problem, escape the language, you see that the problem does not actually exist at all. The whole problem, in its is entirety, is not a real problem, but an imaginary one.

You can construct very complicated, hypothetical scenarios with language, and these scenarios can become very serious problems for your mind, but they are not real problems: they are abstract, hypothetical ones. We can argue about them all we want, but we only make progress when we perform objective tests. We cut down a tree, where we are both witnesses, and determine whether it makes a sound or not. We could create an experiment in which we do not record the results but what would be the point? It would not even be a true experiment.

What I am trying to do here is to get people to realize that hypothetical problems are not real: they are hypothetical. If something is hypothetical, it only "exists" in the imagination. If it only exists in the imagination, then it is subject to the laws of the imagination, not the laws of reality.

As for time, the limit of your argument is the language. It is hard to break free of this limit, because language is so linear and time-biased.

Let me suggest that although we all perceive movement and molecular change, that we imagine time to be the dimension along which all of these things take place. The dimension itself is the imaginary concept, not the actual changes or movements that take place.

Instead of time, let's imagine a Blue dimension. Everything can be measured on the basis of how blue it is. It is easy to create a blue dimension and order things along its axis. Then we can argue about whether something is blue whether or not someone is there to perceive it.

However, the blue dimension is a linguistic construct. There is no blue dimension. It is imaginary. It turns out that blue is just a way of categorizing things that we perceive as blue.

How hard would it be to convince the Blue Meanies that the blue dimension was just a conceptual dimension that they made up to help them put things in proper order of Blueness?

Now, it is easy for us to imagine life without a blue dimension because we have not based so much of our language on it, but it is more difficult to imagine language without a time dimension. The very structure of language is linear. To read this sentence, you read the beginning, the middle, and the end, during which your heart beat 4 times, you breathed once, and the second hand on the clock moved a few degrees. Language is linear. This sentence is linear. We might imagine a dimension for this sentence. It is almost impossible to imagine language that is not linear, and so it is almost impossible to imagine language without time. Time is built into the language, and so we cannot escape the concept...but, if you accept the idea that our concepts are language-based (like the tree problem) then you see that time is just a linguistic construct. It is very useful, so useful that it is impossible to relate thoughts without it, but a construct nonetheless. We cannot measure time directly: we can only count occurrences of events, and order them by which we perceived first. We then construct an imaginary line and put tick marks on that line to indicate their relative placement.

A more challenging example: a number...for example the number four. "Four" does not exist (nor does 42,for that matter). You might say: "How do we count things if numbers don't exist, then?" or "There are four pennies on my desk, how can the number four not exist?" The things exist, true, but the numbers do not. Numbers are a mental construct. They are a way that we have of counting things, and working with mathematical abstractions, but the numbers themselves do not exist, except as a mental construct. I have heard someone say "Four is the set of all sets that include four members," but such a definition is circular, but it helps to get the point across. A number doesn't actually exist, but because we all agree on the imaginary construct, and numbers are embedded in our language, and language determines our thinking, it is nigh impossible to accept the fact that numbers, per se, do not actually exist. The number four is just our way of categorizing all sets that have four members. The sets themselves are our way of categorizing and labeling things that we believe are similar or identical (such as pennies). However, we might also consider each penny to be a unique arrangement of copper and zinc atoms, and so our lumping them all together into one category only makes sense on a human level. Maybe this penny has more copper atoms than that one, or this one is more tarnished than that one. They are each unique constructs, but we lump them together into the same category anyway because we dismiss those differences, and the lumping creates a set, and then we count the members of that set and wind up with four members.

So, back to the original point, I'm not arguing that changes do not occur, or that photons don't move through the universe along their pathways and some arrive before others. I am arguing that the "dimension" along which we measure these changes is an imaginary line. So time is a mental construct that we use to describe the order of changes in the universe, but does not actually exist.

[SeeJay]

I would say that 42 explains it all!!! ;-)

[Marvin]

Language is linear. This sentence is linear.

Would that be measured in yards or in meters?