Astronomy Without A Telescope – Time Freeze

50 Replies to “Astronomy Without A Telescope – Time Freeze”

1. Is it ever possible to find yourself in a situation where you see the hands of a clock freeze?

   Yes, that would be trying to open UT pages again. With Firefox; but since it acts up on some other sites maybe it isn’t a privileged UT problem this time?

   Moving on to the subject, I’m not sure I have time for it!? 😀

   And with a remarkably good telescope you might look back and see a distorted and red-shifted Big Ben with its hands running fast.

   True; but the nitpicker in me notes that would only happen on the outbound leg, since the light cone in front of the relativistic traveler is blue shifted.

   because after covering such distances you can never go back – unless it is to meet your very, very, very great grandchildren.

   Perhaps. It is claimed there are general relativity solutions of a rotating universe where after you make a boundary round trip at relativistic speeds you will arrive before you started.

   But those solutions are non-physical in our universe, which is too large and eventually expands faster than light due to dark energy.

   It is fun to ponder that generally these solutions would perhaps not break the time travel problem of computer science. (I.e. no analog systems may break algorithmic resource problems, say by time travel, or digital computers wouldn’t have them.) They would time travel information, but the principle resource problems involved in launching such expeditions would likely not allow real time time travel computation.

   So maybe they don’t apply for (our type of) FRW universes specifically, but in that case there may be some deep principle involved. Or maybe they simply bump up against the GR problem of defining global energy, which is the same as to say you can’t define global conservation over time (since there is no “global time” in GR). The safe bet would be the later, unfortunately.

   1. Nitpick on your nitpick… ‘you might look back and see…’ implies the outbound leg 🙂

      1. You are twisting my neck, aren’t you?

         (Actually, I thought “look back” in english translated to my mother tongue, where you can look back where you originated at all times.)

      2. “look back where” = look back to where.

      3. Would you not look back to Alpha Centauri on the return leg (i.e. back to where you have just been)?

      4. Yes, that would be a new origination place.

2. yes we could travel the complete universe our lifetime but we will never meet anyone ever again of our family since we will live in different times once departed.

3. forgive me if I’m wrong, I’m not really sure of the math, but…

   From a purely subjective POV don’t all the C squareds cancel out so that, as you keep accelerating, it appears to the person accelerating as if purely Newtonian laws were governing their speed and time to target? Your acceleration decreases, but at the same rate as your subjective time decreases meaning that subjectively your acceleration seems to remain constant. etc…

   1. If by subjective time, you mean your time within your frame of reference, no that shouldn’t change. With acceleration, you will change from being in a state of free fall (i.e. constant velocity) to being pushed back into your seat – which will feel like a kind of pseudo-gravity. Acceleration and deceleration need consideration under general not special relativity.

   2. It is good that you ask about uncertainties. Please never apologize for that!

      I’m trying to grasp what those uncertainties are, and I would think that they are more on physics actually.

      It was the genius of Einstein to realize that what you call a “subjective POV” is an objective frame, i.e. that is what you would measure. As all frames are then objectively equally valid, time and space are relative. There is no absolute newtonian global frame to be “subjective” against. What happens to “twin paradox” twins are objective events for each twin (so no actual paradox).

      [Technically there exist a global CMB frame in our universe, a cloud of cosmic microwave background photons that you can measure velocity and red/blue-shift against.

      But that can be seen as a symmetry breaking AFAIU, or in other words it is not a real asymmetry of the underlying general relativity physics. Or in even more different words they are a contingent “absolute” frame.]

4. The return trip with an acceleration is important for the twin paradox argument. The proper time interval of the twin which travels out and back is shorter than the proper time of the twin on Earth

   The stopping of time does occur on a photon, for the T distance it travels is equal to the X distance it travels X = cT, and the distance (or proper time) is given by

   S^2 = (cT)^2 – X^2

   which is zero for the photon. If you are traveling at a velocity v this distance is

   S^2 = (cT)^2 – (vT)^2 = c^2(1 – (v/c)^2)T^2

   And there is a relationship between the stationary time T (chosen on Earth) and the proper time of a moving body with its proper time S

   T = S[1/sqrt(1 – (v/c)^2)].

   This is the infamous Lorentz factor. If v = c the proper time is zero, which happens with a photon.

   This is similar to a distance with the Pythagorean theorem. However, there is that funny minus sign. This is some times referred to as a pseudo-Euclidean space for that reason.

   LC

5. It appears that there is an error (I think) in the last sentence of this paragraph

   It’s only when you check back with Earth that you see that something remarkable is happening. Moving at 99.5% of the speed of light gives you a time dilation factor of around 10. So while someone back on Earth will still measure your trip duration at about 8.6 years – for you it will only be around 10 months. And with a remarkably good telescope you might look back and see a distorted and red-shifted Big Ben with its hands running fast.

   Big Ben’s hands would appear to be slow on the out bound trip (red shifted) as when you arrive at Alpha Centauri you would arrive about 0.5 month after the light wave front that shows you leaving earth, It is on the return trip that the hands of Big Ben run very fast (blue shift)

   Is this right or am I missing something?

   Scottie

   1. I knew I was going to regret that look back stuff. Yes, you are right. Wikipedia does the sums for a 2.57 year there and back trip at 0.8c:

      The twin on the ship sees low frequency (red) images for 2.57 years. During that time, he would see the Earth twin in the image grow older by 2.57/3.73 = 0.69 years. He then sees high frequency (blue) images for the remaining 2.57 years of his trip. During that time, he would see the Earth twin in the image grow older by 2.57×3.73 = 9.59 years. When the journey is finished, the image of the Earth twin has aged by 0.69 + 9.59 = 10.28 years.

      The Earth twin sees 9.59 years of slow (red) images of the ship twin, during which the ship twin ages (in the image) by 9.59/3.73 = 2.57 years. He then sees fast (blue) images for the remaining 0.69 years until the ship returns. In the fast images, the ship twin ages by 0.69×3.73 = 2.57 years. The total aging of the ship twin in the images received by Earth is 2.57+2.57 = 5.14 years, so the ship twin returns younger (5.14 years as opposed to 10.28 years on Earth).

      (From: http://en.wikipedia.org/wiki/Twin_paradox#What_it_looks_like:_the_relativistic_Doppler_shift)

   2. Suppose Big Ben sends a light pulse to you with each second it counts. The light pulses travel the speed of light not matter what. However, the time interval between these pulses can change. As you run away from Earth the time interval between each pulse is increased. Then on the return trip the time interval is much shorter than a second.

      There is a bit of misunderstanding which happens here. The Lorentz gamma factor and the Lorentz boosts tells us that time measured on some frame moving with a speed close to the speed of light is seen to slow and further ruler distances along the direction of motion contract. This is the case, but if you observe a body moving close to the speed of light it requires photons to leave that body and reach you. When you factor that part into the situation things change. There are further strange rotations (Terrell rotations) and other spatial variations which occur.

      http://www.youtube.com/watch?v=JQnHTKZBTI4

      With the twin paradox there is an added complexity of one observer boosting to multiple frames, or acceleration. The acceleration takes the frame off of an inertial frame which determines the longest proper time, spacetime interval or length as measured by a clock on that frame. So by accelerating the path or time length is shortened. For this reason if you fall into a black hole and try to accelerate back out, you in fact hasten your encounter with the singularity where you meet your demise.

      LC

   3. More right than me, I confused red shift with blue shift effects.

6. If “now” doesn’t exist, then why should the rest of it?

   All time is, is a prophet looking backwards wishing that the future will continue to happen.

7. Funny. “In the beginning God created the heavens and the Earth…” but he didn’t make time. Why is that?

   1. Because time is part of a process, not an agent, and processes are mightier than agents that obeys them. It is the same “la la la, I can’t hear you” rationalization that happens for the problem of which agent created the next agent.

      For processes there are several options of “why time”. Environmental selection is the easiest basic example to grasp perhaps, nothing much happens where time doesn’t exist. 😀

8. At .999 c a 1 microgram grain of dust has a kinetic energy of 44.5 megajoules and you will definitely age prematurely if you hit that without a shield. Even a single hydrogen atom will have an energy of around 2,7 microjoules and there are 20-50 of those per cubic centimeter of cold ISM of so you won’t see much on the way back because every square centimetre of your ice shield will be colliding with between 6 and 15 million atoms per second.

   1. You are correct here. Interestingly Arthur C. Clarke’s book “Song of Distant Earth” (1987) explains more generally with his Magellan space ark fleeing Earh destruction. The whole premise is an worn ice shield boring through light-years interstellar space at 0.3-0.4 times the speed of light. The depletion of the ablation shield though fifty light years of space. (Chapter 11, pg.31)
      Even if made of steel, the consequences would be devastating on some interstellar spacecraft.

      1. For those willing to weld out the stickle, the actually page to read is pg.51 not pg.31.

9. To my mind it’s all just a ‘thought experiment’, because you’d have to change the ‘status’ of what you’re made of in order to travel at the speed of light, which really isn’t a ‘speed’ at all, it’s the Ratio of Space to Time. You’d have to become composed of things that have ‘no Inertia’.

   At any speed greater than 0.10 c (apx) I suspect you’ll have a catastrophic collision within 10 years, with some sort of unavoidable lump in the ISM big enough to do fatal damage to your vector vehicle. [which is btw, why THEY aren’t here !] You can’t get from here to there (or vice-versa) at a high velocity ( 0.10 c or greater) because it would require too great an amount of energy to move your ‘ship’ around interveining objects on your path. And at greater speeds you would not have enough time to maneuver around objects, nor have advanced enough warning of them. And there is so much ‘stuff’ out there to run into !!! And that’s the main reason why ‘aliens’ aren’t here ! Too much stuff to run into, and it takes way too long to get here, from there, at any ‘safe speed’.

   1. the Ratio of Space to Time.

      There is no such ratio, since there is no process where space moves against itself, how could it be. Velocity of light is the traversed length interval per time, same as for other objects of course.

      And that’s the main reason why ‘aliens’ aren’t here ! Too much stuff to run into, and it takes way too long to get here, from there, at any ‘safe speed’.

      To repeat myself, feasibly space faring civilizations can do Oort cloud jumping, where they take advantage of the “stuff” they run into. They travel in it and uses it for fuel, and their biospheres should have no more problem with deep time than others.

      As for why they “aren’t here”, existence of a (putative) phenomena and observing it isn’t the same thing.

      For instance, if species adapts to Oort cloud habitation, why on Earth (or other exoplanets) would they want to go down the gravity well? It would cost energy, resources would be scarcer, they would be less adapted to the different environment.

      And ultimately landing, contact with other species and so on would be unlikely, they wouldn’t have the technology, and it would be dangerous even if they wanted to (re)develop such technology.

10. OK, Perhaps a dumb question, I am an average guy. But, if time stands still looking at an object your moving away from at near the speed of light.. doesn’t it accelerate with the objects in front of you? I mean if you were moving away from all sources of light fine, but there will also be light moving toward you from the objects your moving toward.. right?

    1. Again, never apologize for asking!

       Actually, time never “stands still” for an observer or what he observes. (Except that you can make a technical exception for light.*) But relative to the observer time for a moving object may appear differently.

       The post now describes what you asks for, I think, in the sentence starting “And with a remarkably good telescope …”. Or you could follow the link I gave.

       [* You could say for light photons in vacuum traveling at, well, light speed of vacuum, that their time “stands still” between emission and absorption, and get away with it in the physics.

       This is, I think, a result of quantum field theory. Since photons are part of the EM field, the field wave packets may in some case be taken as coexisting “within the field”. They emerge when electric charges are accelerated (as in an antenna) so they can coexist with an existing field obviously.

       During emission and absorption the process is that of a “near field” coupling, and the photons loose their character. No more vacuum light speed (“near fields” behave differently than classical mundane “far fields”) and time becomes relevant. “Oh, I’m being absorbed. I’ve been lonely, but finally something happens around here!”]

11. Non-scientific nitpick: The face is on the Great Clock of Westminster. It’s the bell which is actually called Big Ben.

    1. And therefore you could never see Big Ben even if you were standing still, unless you were inside the clock tower and then you would hurt yourself as you accelerate away by banging in to a wall/glass clock. The mind boggles! 😉

12. Peter, I loved your question. Remember, it’s all relative. If you leave the earth at near light speed than your experience of time will slow compared to those living on IT. But at the same time, you are moving into someone else’s future. How will that work when we get those ships going? Phone your friend in the Centauri system to say I’ll be there in a flash and what happens? They’re always dead by the time you get there because their clocks were zooming forwards the whole time you approached at near light speed. What I don’t understand is if by speeding TOWARDS Earth, you see their time speed up then what happens if you just orbit earth at near light speed? It seems to me that if you’re going in ANY direction at near light speed compared to sluggish Earth, then time should dilate for you and you will not age at your brother’s pace.

    1. If you leave the earth at near light speed than your experience of time will slow compared to those living on IT

       Feeling nitpicky today, I’m going to point out that “your experience of time” *never change*, because it is, well, your experience of time. It is the *relative* experience, observing time relative to other spacetime frames, that changes due to relative differences between the frames (say, relative velocity).

       you are moving into someone else’s future.

       Similarly nitpicking the essentially same mistake: we are _always_ “moving into the future” as time increases, it just happens at different relative “rates”.*

       * “Rate of time” doesn’t actually makes sense, there is no d(tau)/dt = gamma dt/dt = gamma in a physical sense. (I.e. the gamma factor exist but the first differential is ill defined what I know of, being from different frames and all.) But you can *say* that there is such a thing, it makes a sensible analogy even if it is a phony picture.

       I’ve seen many crackpots ponder the “physical meaning” of “rate of time”. Sigh!

       what happens if you just orbit earth at near light speed?

       Now there are some complications, such as the acceleration from the Earth gravity field and the orbital acceleration it causes. (Or rather likely in the last case, mostly the rockets needed in addition to keep you on such an orbit.)

       But in essence you are right, it is enough with a relativistic relative speed to note these effects. Orbiting GPS systems have all of these problems, they correct for both special (this) and general (the above) relativity effects. And they go nowhere near light speed!

    2. “Phone your friend in the Centauri system to say I’ll be there in a flash and what happens? They’re always dead by the time you get there because their ”

       No, they will have 4-5 years at their clock passed, and you, the traveller has experienced maybe an hour.

13. “Slip streaming” will become a popular term in the near future for travel that allows the warping of space & time continously. It’s basically the resetting of matter that allows objects to pass (or slip if you will) through newly formed holes. So basically without letting the cat out of the bag, worm holes inside of other worm holes that continue on doubling in factor until the desired destination is reached. You’ll be suprised how fast Million’s of LY’s passes in just a few days, it’s a one way journey though and you can’t go back even if you liked too.

    It’s the Higgs Field on steroids that actually redirects an object through matter, like passing through walls because they were broken apart at a molecular level. Size doesn’t matter in a vacuum & actually promotes expansion, which is what helps the speed.

    You’ll read about it in about 12 years, after the LHC gets their magnets hot enough to do business in 17′ instead of 17 miles. That’s the trick that does it.

    Goodluck to all.

14. thanks for the interesting responses

15. Mr. Nerlich,
    I thought that because time was relative, the neurons in your brain would continue to fire just fine. It seems every scientific explanation of light speed travel has made it clear that any and all observations were different due to perspective. So, based on my understanding, it would appear no neurons were firing (from one viewer’s perspective); however, in all actuality, that person would be operating at “full brain speed,” so to speak, while his entire vehicle travelling at light speed experiences time differently. Am I misinterpreting what I’ve seen from Neil DeGrasse Tyson and Michio Kaku?
    Thanks,
    – Josh

    1. Hi Josh – no disagreement here. If you could travel at the speed of light, you would not experience the passage of time. But then I seek to then explain why this is probably an impossible situation to find yourself in.

       As several commentators (including me) have noted above, your ‘proper’ time never changes – regardless of your velocity. And I have suggested that you will never quite get to light speed whatever you try to do.

16. Shouldn’t light ahead of you be blue-shifted? If so, you might get radiation poisoning.

    1. Yes – x and gamma rays will be a problem.

17. I see it this way. Time is NOW at any given place/point in our perceived universe or even outside (if there is an outside). An event that occurs at some place/point happens at the exact “instant” at every other place/point. Our physical limitations are what keeps us from experiencing NOW ANYWHERE else but HERE. NOW is now and what we see a light year away is now minus THEN (the PAST), so THERE.

18. Okay, it was an attempt at a little humor.

    1. Très tristement, il n’est aucun drôle égal.

19. I think you missed my point. “Now” doesn’t exist. because it cannot be isolated, only the past “nows” and future “nows can exist.
    Of course, which most have not mentioned here, does time exist below the planck length (10^-35 metres)? Is its causation of spacetime and time come from the quantum foam to make reality in the larger world? (It is more of a quandary if special relativity even woks on these very small scales.)

    1. Oh no, I’m off on a wild goose chase again. Someone shoot me!
       Your right, “now”, lies somewhere between past and future but, since the future hasn’t taken place yet, it must be found somewhere between past and “now”. I’ll go with “now”.
       Quantum foam (whatever it’s makeup), must exist in a dimensional space at some “NOW”. I hope I was clear that I used big NOW to indicate now everywhere.

20. The experience of “now” is the past. This is because there is a lag from 0.000… sec to when the mind reacts to be aware of time passing has already moved on milliseconds after it has happened. Our own psychosis only makes sense of time, being usually termed subjective time, and in reality is an interval and not an absolute fixed ‘zero point’. For this reason “now” is also called specious present.
    Logically, if “now” doesn’t exist, them neither does the past of future exist.
    As for quantum foam, there is no proof that time “must exist in a dimensional space”. That is mere supposition. (Vous faites des suppositions singulières.) The very definition of quantum foam is that you can never know the nature of spacetime or even how it would behave. The virtual particles created may manifest themselves as space, but the vacuum energy itself may not.

    1. But, your speaking metaphysically. I know this has been beaten to death and I’m sure you have better things to do with your time but, I contend space and time exists regardless of sentience.
       “that is mere supposition.” But, isn’t what exists at the Planck scale just that? I say if something exists, quantum or otherwise, it must exist in some kind of continuum, if I may use that word.

    2. Ah, Berkley’s “If a tree were to fall on an island where there were no human beings would there be any sound?” Don’t you just love the anthropic principle.

       In the small quantum mechanical world the existence of many things are not necessarily the same reality as the larger world. Talking about the dimensions in the vacuum energy (zero-point energy) is nonsensical (and also unobservable) just as is believing it is some kind of continuum. If time does somehow originates from the quantum world, talking real dimensions in a world that doesn’t have dimensions in the sense we normally understand is also nonsensical.
       However, in the quantum world is part of our universe and does have real consequences in the universe at large. I.e. Casimir Effect. From it we can calculate the nature of particles and various fundamental constants. I.e. The electron g-factor with quantum electrodynamics (QED)

       1. I didn’t think you would respond again. I grew up using forest instead of island. And I don’t love it nor subscribe to it. Those elements are the same whether they are molecular conglomerates making up my organisms or a conglomeration of them making up my car. A space rock has no sentience but it resides in the same universe and obeys the same physical laws as we blobs of biology do.

          These arguments always haunt. I wished I left the gate a bit earlier than I did but, maybe my late start has it’s advantages although my aging neurons don’t fire in harmony like they use to. I just can’t wrap my head around something being dimensionless or even “zero” point. I shouldn’t have used the word continuum.
          “I.e. Casimir Effect. From it we can calculate the nature of particles and various fundamental constants.”
          But, we do observe these phenomenon in our spacial dimensions. Unobservable does not mean it doesn’t exist. we can’t see space but it must be there to support the “stuff” in it. Even vacuum energy must have a place to reside. Okay, I’ll go away now.

       2. I didn’t use the quote of the Casimir Effect to supplant the word continuum. I used it to describe quantum world has real effects in the ‘real’ world.
          The quantum vacuum or zero-point energy is BOTH nonsensical AND unobservable. (I did never said or inferred; “Unobservable does not mean it doesn’t exist.”) Nonsensical existence? (an oxymoron?)
          Vacuum energy does not have a place to reside or exist in the dimensional world as you and I do know. (That is why it is called quantum foam) Indeed the very notions of spacetime and relativity breakdown below the Plank length. The word “reside” is meaningless, because there is no place that can be “put in a box.”
          As for “But, we do observe these phenomenon in our spacial dimensions.”
          The virtual particles created from the zero-point energy are real dimensional objects, the quantum vacuum itself isn’t; at least in the way that common sense ‘space’ would suggest. I.e. Dimensional Space is not the same as quantum space!!

          (Our modern conception of the physical universe thus embraces both the existent and the non-existent! It is a difficult concept to grasp, but it seems to be true. It is not some fantasy, EU/PC notion, or some personal theory, but how the universe works below 10*-35!) metres.)

       3. Not to say Wiki has the last word but according to it’s “vacuum state” definition;
          “According to quantum mechanics, the vacuum state is not truly empty but instead contains fleeting electromagnetic waves and particles that pop into and out of existence.[3][4][5]”
          If I read this correctly, these waves and particles must pop into and out of some kind of “dimensional” space. If not, what am I missing?

       4. “I grew up using forest instead of island”
          Berkley’s original analogy wasn’t as quote, though it was his idea.
          The form as we know it today appeared in 1883. and this placed it on an island, as did Scientific American. It probably from the words; “no man’s an island.” (then maybe they read Robinson Crusoe as a kid!)
          Island, forest… But hey! No one was there, so no one noticed!

21. Ah, Berkley’s “If a tree were to fall on an island where there were no human beings would there be any sound?” Don’t you just love the anthropic principle.

    In the small quantum mechanical world the existence of many things are not necessarily the same reality as the larger world. Talking about the dimensions in the vacuum energy (zero-point energy) is nonsensical (and also unobservable) just as is believing it is some kind of continuum. If time does somehow originates from the quantum world, talking real dimensions in a world that doesn’t have dimensions in the sense we normally understand is also nonsensical.
    However, in the quantum world is part of our universe and does have real consequences in the universe at large. I.e. Casimir Effect. From it we can calculate the nature of particles and various fundamental constants. I.e. The electron g-factor with quantum electrodynamics (QED)

22. If I google “if a tree falls….” or “if a tree were to fall…” I get “forest” >9 out of 10 hits. I didn’t find “island” although I did give up after 7 pages. I had to google “‘Berkeley’ if a tree were to fall…” to get island. This is probably the reason most say “forest”. Personally, I like island better; it’s more remote.

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