Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Is everything at the same point, when travelling at light speed?


Recommended Posts

Im trying to get my head around this... Ive heard it said a few times, on a few programs (i think brian cox said it), that when you're travelling at the speed of light everything occupies the same point. You no longer experience time, so you are effectively occupying every point at once.

If that is the case, then what is the difference between that, and the big bang?

If you can think of the universe spreading out before you as you slow down from light speed, then that sounds to me like what we are experiencing now.

Link to comment
Share on other sites

The universe is made of two sorts of stuff. Matter always travels at less than the speed of light. Radiation always travels at the speed of light. (A third sort, "tachyons", would always travel faster than light, but is hypothetical, and there's no evidence for its existence).

Radiation doesn't experience anything, so it's meaningless to ask what it would "feel" like to travel at the speed of light. But we can say it in a loose metaphorical sense.

Einstein's theory of relativity provides a way of establishing the four-dimensional "distance" between two events at different places and times. There are three types of separation between events. If it is "timelike" then in any reference frame ("point of view of an observer") we see one event happening after the other. If it is "spacelike" then in any reference frame we see them happening at two different places. The intermediate case is called "lightlike" or "null", which corresponds to a four-dimensional distance zero. Hence the comments by Cox etc. If there were a reference frame where you could make light stand still then everything on a light beam's path would be at the same place and time. But there is no reference frame where you can make light stand still (this is basically what occured to Einstein when he was about 16 though it took him a few more years to make sense of it). So the Coxism should be regarded as metaphorical, not a statement of physical reality.

This is distinct from the Big Bang. If we think of that in reverse, we could picture an infinite universe in which the spatial (3-dimensional) distances between points are shrinking as we go back towards the singularity. At the moment of singularity all separations become zero. Putting it back the right way round, we could say that the Big Bang is the instantaneous appearance of an infinite universe in which everything immediately starts to separate. It therefore happens, so to speak, everwhere at once.

Notice that in speaking of the Big Bang we have separated time from the 3 dimensions of space. This makes mathematical and physical sense, and is why we can speak of the "age" of the universe. In Cox-speak we could say that photons "think" the universe has no age at all. But the overall separation of galaxy clusters etc (the "Hubble flow") establishes a standard reference frame for judging the age of the universe.

Moral of story: popular science is often only parable, not to be taken literally. The truth is in the maths. But maths is hard, hence the parables.

Link to comment
Share on other sites

Great post this one. The idea of all light in the universe occupying one point is a mind boggling concept, and one that I had never heard of before. Of course it makes sense when you think about it, but it's something that can easily go over your head. It makes you realise how connected everything must be.   

Link to comment
Share on other sites

  • 2 months later...

Perhaps I heard the same thing? I used i-player about 10 times to repeat one of Brian Cox's comments, some years ago, because I just couldn't get it. Martin Rees & Patrick Moore were on the same program and it was clear that Patrick did not understand what Brian had said. My final interpretation was...as far as a light particle is concerned, it gets to where it is going, no matter where it is going (even to the end of the universe) immediately...as a body gets closer and closer to the speed of light, an external observer sees the clock of that body running slower edging towards time stopping. So, for the light particle, no time has passed and consequently, as far as the photon understands it, the external observers time has run much faster and is edging towards infinity.  Imagine after one year, the photon hits a perfect mirror and then returns to the external observer. After two years the observer sees the photon. The photon says no time has passed, the observer says two years have passed, because he's gone round the sun twice! 

Link to comment
Share on other sites

OK, after writing the above and posting, I'm sure I got it wrong. Another try.....my latest final interpretation(!) is...as far as a light particle is concerned, it gets to where it is going, no matter where it is going (even to the end of the universe) immediately...as a photon (from the external observer's world, light has a wave/particle duality) gets closer and closer to the speed of light, an external observer sees the clock of that body running slower edging towards time stopping. So, for the light particle, all is normal, but as far as the photon understands it, the external observers time has also run much slower and is edging towards zero. Both the photon's frame of reference and the observers frame of reference indicate that their own existence is normal and that the others time has slowed down to close to zero. So after one year (observer's frame of reference), the photon hits a perfect mirror and then returns to the external observer. After two years (observer's frame of reference) the observer sees the photon again. The photon says no time has passed (photon's frame of reference, because it has traveled at the speed of light, and all has been normal), the observer says two years have passed (observer's frame of reference does not allow his own "true" matter to travel exactly at the speed of light, otherwise this matter would have become infinitely heavy and have infinite energy), because he's gone round the sun twice! Time (and length) do not exist as independent  invariable properties, they are "warped" in the presence of matter. 

Link to comment
Share on other sites

Perhaps I heard the same thing? I used i-player about 10 times to repeat one of Brian Cox's comments, some years ago, because I just couldn't get it. Martin Rees & Patrick Moore were on the same program and it was clear that Patrick did not understand what Brian had said. My final interpretation was...as far as a light particle is concerned, it gets to where it is going, no matter where it is going (even to the end of the universe) immediately...as a body gets closer and closer to the speed of light, an external observer sees the clock of that body running slower edging towards time stopping. So, for the light particle, no time has passed and consequently, as far as the photon understands it, the external observers time has run much faster and is edging towards infinity.  Imagine after one year, the photon hits a perfect mirror and then returns to the external observer. After two years the observer sees the photon. The photon says no time has passed, the observer says two years have passed, because he's gone round the sun twice! 

So is this the principle of time travel in the movies?

In essence if we can get to the speed of light (which we know we cannot) then we could travel anywhere with no 'movement' in time.

Link to comment
Share on other sites

The way i think of it, is that there is no mirror for the photon to hit... there is nothing to hit... because as far as the photon is concerned everything is at the same point in space.

Actually... that is even stranger... Because if time stops for the photon, and everything in the universe is effectively at the same place, then how can you say that the photon is moving? Its a bit silly to say that it is travelling at a speed (light speed) when it no longer travels between two points. If everything is at the same point then it makes more sense to say that light speed is zero.

I know i should have paid more attention at school because its too confusing...

Link to comment
Share on other sites

Its all quite simple really - if you accellerate away into space and travel close to c then your own clock slows down relative to a "rest" clock. So to get to Andromeda seems to take no time at all, although when you get back to the UK about 5 million years will have passed (humans may have changed as much as they have since the very early hominids). Travelling at the speed of light means you can get anywhere in no time at all (as measured on your watch), but that is because it's just the same as being frozen and thawed out at the other end. The Andromedans (when you popped in) have had 2.5 million years of evolution before you arrive and have gone from being peacable benevolent aliens to rabid "world of tanks" cyber intelligences. You are not "everywhere at once" - you just dont't notice the travel time (delays, snow on the tracks etc).

P

Link to comment
Share on other sites

I have to say that as brilliant as the celeb physicists can be at explaining things to the jo public sometimes I think they are guilty of seriously overcomplicating things. And explanations of time are definitely in that category. Now it may be that as the passing of time is relative to the observer then so the meaning of time is relevant to the individual but I see time as this. Time for me is nothing more than a measurement of the passing of processes. A pointer in the direction of the flow of chaos. For me time surely cannot really exist or at least not independently of natural processes. If all processes in the universe were to suddenly stop then time to would stand still, the moment processes started again time to would start. Therefore using the above thought all you need to know is that the faster a body travels the slower the processes associated with that body take place. This we know to be true (predicted by Einstein) proved by GPS satellites which have to have their clocks regularly adjusted or your sat nav would be as accurate as a mother in laws directions. So if you were travelling at c your processes would slow considerably (you would age little) whilst over a given period those "stationery" would seem to age greatly. I once read a book that put it as a graph where one axis was time and one axis space, simply the greater pitch rises on one axis then the less it rises into the other.

I have to say though I don't get the no time passing for light. Even light takes time to travel across our galaxy so yes it may seem just a hop for light but even it must concede its not instant?

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.