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Does the past exist?

13

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  • Closed Accounts Posts: 6,718 ✭✭✭SkepticOne


    mangaroosh wrote: »
    apologies for re-iterating, but, we are not actually looking at something from the past, what we are seeing is the rays of light as they reach the earth in the present moment.
    This is true, but if we get rid of the concept of the past and the future, how do we account for these rays of light? The normal explanation is that they are emitted by stars and the light takes several years to reach us. What is the explanation you might offer without using the concept of time. In fact how do we explain present events in general without invoking ones in the past?

    That is why I would say the past exists. It is a concept but a necessary one.


  • Closed Accounts Posts: 767 ✭✭✭HxGH


    dungeon wrote: »
    Now I remember why I dropped Physics and Chemistry!

    I kept physics.. I may need it to see how long I have to wait to see my computer smash off the ground from an 80 metre height.


  • Registered Users Posts: 689 ✭✭✭JoeB-


    A nice way of seeing the end of the universe would be to jump into a black hole... as you cross the event horizon the time dilation will become so severe that you will see the end of the universe outside the black hole.

    Another way of thinking about this is that as you approach the black hole the light, or radio signals that you emit will take longer and longer to emerge from the area of the black hole.. and as you cross the event horizon any signals you emit would take an infinite amount of time to escape... so we can't find out the future by dropping a probe into a black hole..the signals would become fainter and fainter as the same amount of energy is stretched out over a longer and longer time frame.. (and as light is quanticised this must introduce an additional complexity, as only whole photons can be emitted)


    As you approach a black hole, or another massive body, your subjective time will go slower, and objects far away from the black hole or massive body will appear speeded up... and as you cross the event horizon they will be speeded up an infinite amount, and so you see the end of all things, and God and the Devil fighting things out...

    Of course it is more likely that current physics is wrong, and that something else happens, like a spaghetti dinner..


  • Registered Users Posts: 4,611 ✭✭✭maninasia


    Does this not though just prove that the past existed? It doesn't quite prove that it still exists right?



    That's pretty much what I was getting at in my original post. The people and moments of the past, will they always exist? I know they existed once in what they perceived as their present but somewhere in the universe are they still existing or, as some have pointed out, is there no past but the present and is it all to do with perception...

    Incidentally could you tell me the novel with that quote as it sounds quite interesting. :cool:

    I think the past exists in it's own past, we exist in our present, and the future exists in itself. It is our perception that we are 'now', that they are 'past' and that is 'future' which is also the issue. From the perception of the person in the past at that moment, the moment is 'now', while he would perceive our present moment as the 'future'.

    Does it still exist....I think this question is due to your mode of understanding, much like does God consist of three parts. Well no-one who is an atheist would even bother asking such a question.

    Time is a construction in our heads to make sense of entropy, or 'the tendency of an ordered state to become disordered'.


    Can we go from our 'present' to enter another 'present' (to us it could be past, now-in a different place, or future). It is a different place in spacetime..and we would enter that space and therefore cause it to be different by us being there, so even if we went to that time it may create a new spacetime, we may not actually visit the place we thought we were visiting.


  • Registered Users Posts: 2,593 ✭✭✭Sea Sharp


    I've always had trouble with time being the fourth dimension because I don't think it's a dimension in the same way as the first three location dimensions. (length, width, height.)
    I don't think the past exists but the present is a butterfly effect consequence of the past. The present is a redistribution of the matter and energy of the past.


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  • Registered Users Posts: 1,210 ✭✭✭20goto10


    Anything that could possibly happen is happening and it's all happening all at the same time. Somewhere out there, in an infinite universe filled with infinite possibilities, I exist 2 seconds ago and 10 years ago. Assuming infinity is not just an illusion and me existing 10 years ago at the same time as now is an actual possibility in an infinite amount of outcomes....which it is I suppose since the outcomes are infinite.


  • Registered Users Posts: 2,552 ✭✭✭roosh


    SkepticOne wrote: »
    This is true, but if we get rid of the concept of the past and the future, how do we account for these rays of light? The normal explanation is that they are emitted by stars and the light takes several years to reach us. What is the explanation you might offer without using the concept of time. In fact how do we explain present events in general without invoking ones in the past?

    That is why I would say the past exists. It is a concept but a necessary one.

    the thing is, we don't have to get rid of the concepts of past and future, rather just realise that that is what they are, merely concepts, with no intrinsic existence. Past and future exists solely as concepts in the mind.

    They are useful for explaning things, perhaps due to our reliance on the concpets. That could perhaps change as a deeper understanding develelops among mankind. It of course may not change either.

    but yes, the past is a useful concept (at present - pardon the expression), however the nature of it, is such that it doesn't actually exist, other than as a thought form, in the mind.


  • Registered Users Posts: 5,848 ✭✭✭bleg


    http://www.youtube.com/watch?v=8Q_GQqUg6Ts


    Imagining the 10th dimension


  • Closed Accounts Posts: 42 imincanada


    What about string theory and the creation dimensions?


  • Registered Users Posts: 3,457 ✭✭✭Morbert


    bleg wrote: »
    http://www.youtube.com/watch?v=8Q_GQqUg6Ts


    Imagining the 10th dimension

    I know this thread is effectively finished but I need to voice my usual disclaimer and say that that video in no way represents any physical theory of spacetime.


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  • Closed Accounts Posts: 2,616 ✭✭✭FISMA


    OP
    This question is really going to go more to MetaPhysics than Physics. The past is really something that Science does not like to question.

    First - what is your scientific test to demonstrate that your memory is working properly? Answer - there is none.

    The past is a mental construct. Is it in our brain or our mind?

    The past works well in science - we are happy with say F = ma. eg I apply a force and the mass accelerates. We are left with the distinct impression that the past has a causative effect on the future. With this we are comfortable.

    However, the equations of Physics are time reversal symmetric - they work equally well into the future as they do in the past. This implies that our present actions should influence the past... What??? :eek:

    There are numerous instances where your brain takes shortcuts and that your eyes fudge what they see: both in an attempt to keep it simple. If we know and can demonstrate that our two most prized biological gifts are so flawed, to what extent should they be relied upon?

    If we are to test the past, how would we demonstrate that our memory is functioning properly? More importantly, if we can change the past, what does this do to the aforementioned test?


  • Registered Users Posts: 26 Bert Halligan


    FISMA wrote: »
    OP

    However, the equations of Physics are time reversal symmetric - they work equally well into the future as they do in the past. This implies that our present actions should influence the past... What??? :eek:

    There are numerous instances where your brain takes shortcuts and that your eyes fudge what they see: both in an attempt to keep it simple. If we know and can demonstrate that our two most prized biological gifts are so flawed, to what extent should they be relied upon?

    If we are to test the past, how would we demonstrate that our memory is functioning properly? More importantly, if we can change the past, what does this do to the aforementioned test?

    I read a very interesting article some time ago in new scientist which was questioning whether by observing the cosmic background radiation we had changed the outcome of the "experiment" of the big bang. Mind bending stuff but then quantum mechanics generally is, at least for my humble brain anyway.

    Didn't Einstein say something along the lines of the illusion of linear time would possibly be impossible for the human mind to overcome?


  • Registered Users Posts: 144 ✭✭gentillabdulla


    I was watching a documentary on time travel recently and something one of the scientists said interested me. He was talking about the past as if it was something legitimate in the universe and that it exists in some form. I am wondering what science officially makes of this? Does the past exist in the eyes of science? I hope I'm making sense.

    For example, about a half an hour ago I made myself a cup of tea. Is there somewhere in our universe where this is still occurring even though as I write this I'm thirty minutes past that point?

    Important historical figures from centuries ago, loved ones we have lost, obviously they are dead to us at this moment but do they exist out there in some capacity beyond our reach in the past? Are their lives imprinted on time?

    Just curious what the general concensus of the scientific community is on this idea? :cool:

    Well I think that the past definitely exists. But when you go to the past you are really in the present past.

    I see it as a number line.

    Say you have the numbers 12345678910111213...

    Just by the numbers actually existing then the past and future exists with it.

    Because you can't just say 5 exists but then say 4 doesn't.

    So lets say you form closed timelike curves.

    When you go into the past the numbers 10 11 12 13 14 15 16 create a loop all the way back to number 5.

    This is where you can see the "Past" in the future.

    You can call this the past future, fast, or pasture.

    Where you go into the past but you are staying in the present relative to you.


  • Registered Users Posts: 45,535 ✭✭✭✭Mr.Nice Guy


    Very interesting piece on this from the Huffington Post by Robert Lanza. A lot of it I found tough to work out but I'm curious what others make of it:
    Does the Past Exist Yet? Evidence Suggests Your Past Isn't Set in Stone

    Recent discoveries require us to rethink our understanding of history. "The histories of the universe," said renowned physicist Stephen Hawking "depend on what is being measured, contrary to the usual idea that the universe has an objective observer-independent history."

    Is it possible we live and die in a world of illusions? Physics tells us that objects exist in a suspended state until observed, when they collapse in to just one outcome. Paradoxically, whether events happened in the past may not be determined until sometime in your future -- and may even depend on actions that you haven't taken yet.

    In 2002, scientists carried out an amazing experiment, which showed that particles of light "photons" knew -- in advance −- what their distant twins would do in the future. They tested the communication between pairs of photons -- whether to be either a wave or a particle. Researchers stretched the distance one of the photons had to take to reach its detector, so that the other photon would hit its own detector first. The photons taking this path already finished their journeys -− they either collapse into a particle or don't before their twin encounters a scrambling device. Somehow, the particles acted on this information before it happened, and across distances instantaneously as if there was no space or time between them. They decided not to become particles before their twin ever encountered the scrambler. It doesn't matter how we set up the experiment. Our mind and its knowledge is the only thing that determines how they behave. Experiments consistently confirm these observer-dependent effects.

    More recently (Science 315, 966, 2007), scientists in France shot photons into an apparatus, and showed that what they did could retroactively change something that had already happened. As the photons passed a fork in the apparatus, they had to decide whether to behave like particles or waves when they hit a beam splitter. Later on - well after the photons passed the fork - the experimenter could randomly switch a second beam splitter on and off. It turns out that what the observer decided at that point, determined what the particle actually did at the fork in the past. At that moment, the experimenter chose his history.

    Of course, we live in the same world. Particles have a range of possible states, and it's not until observed that they take on properties. So until the present is determined, how can there be a past? According to visionary physicist John Wheeler (who coined the word "black hole"), "The quantum principle shows that there is a sense in which what an observer will do in the future defines what happens in the past." Part of the past is locked in when you observe things and the "probability waves collapse." But there's still uncertainty, for instance, as to what's underneath your feet. If you dig a hole, there's a probability you'll find a boulder. Say you hit a boulder, the glacial movements of the past that account for the rock being in exactly that spot will change as described in the Science experiment.

    But what about dinosaur fossils? Fossils are really no different than anything else in nature. For instance, the carbon atoms in your body are "fossils" created in the heart of exploding supernova stars. Bottom line: reality begins and ends with the observer. "We are participators," Wheeler said "in bringing about something of the universe in the distant past." Before his death, he stated that when observing light from a quasar, we set up a quantum observation on an enormously large scale. It means, he said, the measurements made on the light now, determines the path it took billions of years ago.

    Like the light from Wheeler's quasar, historical events such as who killed JFK, might also depend on events that haven't occurred yet. There's enough uncertainty that it could be one person in one set of circumstances, or another person in another. Although JFK was assassinated, you only possess fragments of information about the event. But as you investigate, you collapse more and more reality. According to biocentrism, space and time are relative to the individual observer - we each carry them around like turtles with shells.

    History is a biological phenomenon − it's the logic of what you, the animal observer experiences. You have multiple possible futures, each with a different history like in the Science experiment. Consider the JFK example: say two gunmen shot at JFK, and there was an equal chance one or the other killed him. This would be a situation much like the famous Schrödinger's cat experiment, in which the cat is both alive and dead − both possibilities exist until you open the box and investigate.

    "We must re-think all that we have ever learned about the past, human evolution and the nature of reality, if we are ever to find our true place in the cosmos," says Constance Hilliard, a historian of science at UNT. Choices you haven't made yet might determine which of your childhood friends are still alive, or whether your dog got hit by a car yesterday. In fact, you might even collapse realities that determine whether Noah's Ark sank. "The universe," said John Haldane, "is not only queerer than we suppose, but queerer than we can suppose."

    http://www.huffingtonpost.com/robert-lanza/does-the-past-exist-yet-e_b_683103.html

    That last paragraph is pretty wild. Thoughts on this?

    'It is better to walk alone in the right direction than follow the herd walking in the wrong direction.'



  • Registered Users Posts: 4,611 ✭✭✭maninasia


    It's really a complex question. For instance what constitutes an observer...what makes the probabilities collapse until they become 'one' result.
    That is taken as an interaction with the particle/wave which causes it to collapse, in practicality then an observer is just something that interacts. We can be an observer by interacting in whatever form, but so can a snowflake or a raindrop or another atom or ion or electron or photon.

    The article mentions how particles can somehow be linked...spin correlation. I have tried discussing this with physicists before, suffice to say it is hard to use common sense terms for what is not common sense. Some physicists say there is no instantaneous connection because the particles are already correlated when they are split off...much as if you split a single playing card in half and shot it off in opposite directions, when you turn it around they will always give the same suit/number.

    Due to the phenomenon of the uncertainty principle I believe it is impossible to predict the future. Therefore we cannot go the future accurately and it is also possible that the future branches infinitely. However we should be able to go back to the past accurately as long as we recorded every single interaction of every wave and particle from that point to this! So we can go 'back to the past' if we have a sufficiently powerful computer and technology, the point in the past we could go awaits our technological abilities to develop.

    Or if we create a virtual universe we could certainly go back to the past as we know all the parameters. However if the virtual universe had uncertainty built in and had outside inputs we couldn't predict we still couldn't go to the future though as it can't be accurately predicted.

    There is one other way, develop a multiverse computer that works in higher dimensions. Maybe with such a computer you could predict all futures and all past accurately, you still have to choose one though.


  • Registered Users Posts: 1,005 ✭✭✭Enkidu


    That last paragraph is pretty wild. Thoughts on this?
    It's a pile of nonsense. The classical world, which contains you and your friends, is decohered so none of this stuff can happen at that level.


  • Closed Accounts Posts: 1,042 ✭✭✭himnextdoor


    The main problem I have with the multiverse type theories is that one of the consequences must be that a Universe exists that has violated the law of entropy throughout its entire history. Could a system that flouts the law of entropy even come into existence in the first place?

    That and the fact that in order for a separate universe to exist for all possible outcomes of all possible combination would require the existence of about infinity raised to the power of infinity universes including the ones that are non-deterministic.

    The present could be defined as the configuration of space/mass/energy as it is. 'Now' is the deterministic outcome of how the same space/matter/energy was previously arranged. And the future is the 'yet to be observed' deterministic outcome of now and again, is a reconfiguration of the same stuff.

    Like a kaleidoscope; when you look through the eye-piece you see the pattern as it is 'now, in the present. When you rotate the scope then you alter the present; same stuff, different configuration. Turning the scope doesn't choose a pre-existing alternative universe where the pattern is correct, turning the scope determines what the same universe will look like and how it will behave in the future.

    Or a rain-cloud; one minute it looks like a horse, the next it looks like a woman holding a baby. Then it rains; where is the horse; where is the woman?

    Our telescopes have located objects in the sky that are upward of 13 billion light-years away but are we looking at the past?

    It could be said that the photon energy received from such a distant source has deterministic consequences for us as it contributes to the local energy pool but what do those photons actually represent?

    These photons have always been in the present. They are a result of a deterministic process. We are looking at 13 billion year old photons and not a 13 billion year old galaxy. The galaxy might not exist at all in our present but some of the photons it created do and it is possible to extrapolate data from these photons that relate to their source.

    I think it is safer to say that all events that have deterministic consequences give rise to the present and since there are no other events, the past and future do not exist.


  • Registered Users Posts: 4,611 ✭✭✭maninasia


    The main problem I have with the multiverse type theories is that one of the consequences must be that a Universe exists that has violated the law of entropy throughout its entire history. Could a system that flouts the law of entropy even come into existence in the first place?
    Well yes, because each universe can have different physical laws applying to it. A law is only a law in that particular universe. Also entropy could reverse in the case of a contracting universe, as far as I remember!

    Also entropy can be combatted locally (remember those venn diagrams) it's pretty much how life works. So imagine the case of a massive or infinite universe where the overall entropy increases but locally it decreases, and in fact that is what happens.

    Also we are not sure if laws remain constant across the whole universe or over time.

    Entropy, it's an interesting thing to get our heads round.


  • Registered Users Posts: 4,611 ✭✭✭maninasia


    If the universe was completely recordable past and present are fully accessible and future may be accessible if it has already happened past your timeline.


  • Closed Accounts Posts: 1,042 ✭✭✭himnextdoor


    maninasia wrote: »
    Well yes, because each universe can have different physical laws applying to it. A law is only a law in that particular universe. Also entropy could reverse in the case of a contracting universe, as far as I remember!

    To be honest, I find a Universe controlled by God more satisfying than infinite universes.

    I don't think that entropy can be reversed at all. Ever. It can be tempararily thwarted but not reversed. You might say that puddles of water have a tendency to dry up but the fact that it rains from time to time doesn't mean that that tendency has been reversed, it means there are consequences to puddles drying up.
    maninasia wrote: »
    Also entropy can be combatted locally (remember those venn diagrams) it's pretty much how life works. So imagine the case of a massive or infinite universe where the overall entropy increases but locally it decreases, and in fact that is what happens.

    I don't think there is combat with entropy; entropy is the engine of change and change is constant and, as far as nature is concerned, random.

    Entropy is conserved. I have heard it said that the sun's energy is what drives life on earth and therefore, since organised structure has resulted from it, entropy is lower in this part of the Universe. I think that what has actually happened is that this part of the Universe has gone into 'entropic debt'.

    Sure, the sun provides energy for life but then, why do we have to eat? Because the energy isn't organised enough. By killing and eating, we pay off this entropic debt as it could be said that the organisation of human life results in disorganisation of other natural structures. So we are in fact fulfilling entropic law, not combatting it. We simply take it into account in order to extend life but in the end, we all die and decompose and the sun is just as responsible for that as it is for creating life in the first place.
    maninasia wrote: »
    Also we are not sure if laws remain constant across the whole universe or over time.

    Entropy, it's an interesting thing to get our heads round.

    'Law' is such a strong word, it connotes 'directive'; I prefer 'tendency'. And prevailing conditions affect tendency.

    The earth occupies a certain volume of space but what is the difference between that space and an equal volume of apparently empty space?

    It may be a philosophically moot point but it could be argued that both volumes of space contain the same number of points. Suppose we could zoom in, magnify a point in both spaces; for instance, zoom in on a proton in an atom at the centre of the earth, zoom in on the quarks it is made of, zoom in on the stuff that quarks are made of; keeping zooming in until there is nothing more to zoom in on. What would you see?

    I reckon that the difference between empty space and mass is heat. After all that zooming you would end up with a heat map showing heat distribution; it would indeed look like a kaleidoscope of colour, constantly changing.

    And it would be the same for the space occupied by earth!

    You would be looking at the present; the past has gone, never to be experienced again. The present was determined by the past; the present is the legacy of the past. The future is entirely determined by the present; the future is the legacy of the present.

    Or, to put it another way, if there is only one universe then there can only be one time; the time is now, always.

    But of course, if there is more than one universe then there is more than one time, more than one 'now'. Those other universes will have extinct pasts and unborn futures too though, just like our Universe.

    It's all a head-melt, isn't it? :)


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  • Closed Accounts Posts: 1,042 ✭✭✭himnextdoor


    maninasia wrote: »
    If the universe was completely recordable past and present are fully accessible and future may be accessible if it has already happened past your timeline.

    But a complete recording of the Universe requires every point in space to be accounted for and every point recorded would occupy more than one point. (Each point has infinite variation.)

    The recording equipment would have to exist and the recording medium too.

    You would need an even bigger universe to house the recording.

    In fact, each universe would have to be a single frame, a snapshot, in itself but that would mean that there is no Universe at all, just a recording of one.???

    But where is the projector located?


  • Registered Users Posts: 4,611 ✭✭✭maninasia


    If universes/multiverses are infinite than universes should be recordable and therefore you could take one and play if forward and back with all that handy infinite energy on hand :cool: . You might have to do some approximations to take into account heisenberg's uncertainty principle and other factors.


  • Registered Users Posts: 128 ✭✭Allosaur


    To be totally blunt about it. It doesn't anymore. We can't observe it, it can't effect us. So in reality the answer must be No.


  • Registered Users Posts: 128 ✭✭Allosaur


    topper75 wrote: »
    Independent of our human observation though -

    The light has left the star in the past.
    The light reaches our eyes in the present.

    I don't know how this adds up to mean that the past is still happening.

    By it's very definition, the past is not still happening. No semantics required.
    In that case, the past is happening here. If you want to think in terms of 4 dimensions.


  • Registered Users Posts: 13,080 ✭✭✭✭Maximus Alexander


    topper75 wrote: »
    Independent of our human observation though -

    The light has left the star in the past.
    The light reaches our eyes in the present.

    I don't know how this adds up to mean that the past is still happening.

    By it's very definition, the past is not still happening. No semantics required.

    Interestingly though, from the light's perspective it leaves the star and arrives at your retina at the same time. It's not all so black and white.


  • Closed Accounts Posts: 1,042 ✭✭✭himnextdoor


    Allosaur wrote: »
    In that case, the past is happening here. If you want to think in terms of 4 dimensions.

    If the Universe is all that there is, everything in existence, and 'now' is the current state of the Universe then since there is nothing else but the Universe, the Universe must always be in a current state; the time can only be ever be 'now'.

    I think causality proves this and seems reasonable; when two particles collide then the same two particles change direction and probably lose a little mass as energy in the process too. It is unreasonable to say that an infinite number other pairs of particles each with an infinite number of mass to energy conversion possibilities are created and exist as a different universe for each pair.

    Even to assume that electrons in motion are simply a sequence of different electrons from different universes is unreasonabe.

    It seems much simpler to consider that events cause effects and, deterministically, these effects propogate to cause events; or to think of the Universe as a thermodynamic system; the Universe today is the same as the one that existed yesterday but having a different energy distribution.

    You could say that the process of change is analogous to a process of 'now' becoming the past but that is causal in the wrong direction; our actions can have no effect on yesterday but the effects of yesterday can have an effect on 'now'. Likewise, the future cannot affect a 'now' whereas the past did. And 'now' affects a particular future, a new 'now', deterministically. Same stuff, different configuration.

    I think of the past and present as being books on a shelf; they are written and can be read but they cannot change. But the Universe is a process of change and therefore the book has not been written and cannot be read.

    'Now' is in the writing, now is what's happening. Now is where experience is gathered, forces exchanged.

    Memory of a previous 'now' is not the same as an existent past. Memory is the effect of a previous 'now'.


  • Closed Accounts Posts: 1,042 ✭✭✭himnextdoor


    LeighH wrote: »
    Interestingly though, from the light's perspective it leaves the star and arrives at your retina at the same time. It's not all so black and white.

    But it is a little redder.

    Suppose a photon that has travelled 13-billion light-years passes by a star and finds itself on parallel paths with two other photons; the one on the left has a wavelength that matches the 'old' photon and the one on the right has a wavelength that matches the wavelength that the old photon had when it was first emitted.

    If the old photon perceived no passage of time then wouldn't it have an identity crisis; which one would it be most like?


  • Registered Users Posts: 13,080 ✭✭✭✭Maximus Alexander


    Does it even make sense to ask that question though?

    Let's mix that up a little. Image you jump into a spaceship in the Andromeda galaxy and set course for Earth at exactly the speed of light (somehow).

    As you enter the Milky Way you pass a star and two of your clones climb into their identical spaceships and fly parallel to you.

    You arrive on Earth and climb out to find two identical clones climbing out of theirs. This is the first time you have ever seen them. From your perspective, you have traveled instantaneously from Andromeda to Earth and would thus be completely unaware that your two clones accompanied you for some 50,000 years of your 2.5 million year journey.

    Neither you nor your ship have actually aged a day.


  • Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 90,537 Mod ✭✭✭✭Capt'n Midnight


    But it is a little redder.

    Suppose a photon that has travelled 13-billion light-years passes by a star and finds itself on parallel paths with two other photons; the one on the left has a wavelength that matches the 'old' photon and the one on the right has a wavelength that matches the wavelength that the old photon had when it was first emitted.

    If the old photon perceived no passage of time then wouldn't it have an identity crisis; which one would it be most like?
    The wavelength depends on the frame of reference , doppler shift and all that.

    All three photons will be the same since the old and current one both have the same energy. E = h v

    Unless you are talking about the view from the star in which case the question doesn't have any meaning since a view from another place would produce a different photon ( the earth rotates and orbits so being pedantic you would have to state the time and place you viewed the photon )


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  • Closed Accounts Posts: 1,042 ✭✭✭himnextdoor


    LeighH wrote: »
    Does it even make sense to ask that question though?

    Let's mix that up a little. Image you jump into a spaceship in the Andromeda galaxy and set course for Earth at exactly the speed of light (somehow).

    As you enter the Milky Way you pass a star and two of your clones climb into their identical spaceships and fly parallel to you.

    You arrive on Earth and climb out to find two identical clones climbing out of theirs. This is the first time you have ever seen them. From your perspective, you have traveled instantaneously from Andromeda to Earth and would thus be completely unaware that your two clones accompanied you for some 50,000 years of your 2.5 million year journey.

    Neither you nor your ship have actually aged a day.

    Uh-hu! So red-shift doesn't occur at all?


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