Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Universe Expansion: is it really expanding?

  1. Dec 3, 2012 #1
    Hello everyone.

    Let me introduce myself. I am Curious_Dude. Naturally, by nature, I am a curious person, hence the name. I rarely go on the forums, unless something really bothers me and I just MUST find out, and recently, this question hit me right in the head. This is not a homework question by any means, but more of a "just out of curiosity" question(s), brought to you by: my brain.

    Anyway, everyone knows that the universe is expanding. You ask a person on the street about the universe, if there is one thing they know or heard about it, they'll say:
    To a person who is not stupid and does not believe in everything someone tells him/her, the natural question is:
    Every single scientist or person who knows anything about astronomy will answer them, saying something like:

    However, here is my problem. The assumption of the universe expanding due to everything moving away from us can only be true if AND ONLY IF: We are at the Center of the expansion OR the expansion is not uniform.

    Here is my reasoning:
    let's say you have three cars driving in a line, on a highway at the same speed, and at a distance of say: each 10 meters apart. Then suddenly, two of the cars start to move further away from the middle car. Okay, now here is where it gets interesting. If the speed of all cars did not change, you can only assume that the the distance between each car expanded. The question is, where can the expansion occur in order to cause this change in distance?

    You cannot assume the back of the middle car, because then the front car and middle car would change distance at the same rate, and therefore you would only see a distance change between the middle car and the back (last) car. There would be no difference in terms of distance between the front and middle car. Same thing if you assumed the expansion happened between the front car and middle car, except the result would be reversed. To have both cars change their distance between the middle car at the same rate (definition of uniform expansion), you would need the expansion to happen at the CENTER of the middle car! Right?

    Here's the problem. According to those fantastic telescopes that are never wrong, We ARE NOT at the CENTER of the universe! So how can we claim that the universe is expanding, if everything is moving away from us, and yet we are not at the center of the expansion?
    We would have to see something that is not moving away from us, something moving at the same rate as us, and is moving away at the same rate from the other objects of the universe (just as we are)! And yet, we do not see such a thing. It seems we are the only thing that is somehow changing distances between all these other objects of the universe. So... WTH is really going on then?

    Sure you can say:
    But that would suggest the expansion of the ENTIRE Universe is happening at the center of own galaxy (which is rediculous to claim; even most scientists doubt our galaxy is at the center of the universe; and the universe has billions of them, what are the chances?). But if that were true, again, we would see something that is and something that is not changing distance between us and the other things within our own galaxy. Yet again, we do not see this, and see "everything" moving away from us. Besides, the galaxies seem to be moving at much faster rate away from our galaxy, then anything else moving away from us. However, if that is true, than the expansion of the universe is not truly uniform. Every way I tried to look at this, everything to me suggests that the universe is expanding non-uniformly.

    Ever since I was a child, people told me that the universe is expanding uniformly. I may have heard wrong, I may have read wrong, and this could be a huge misconception in my mind. But if the universe is expanding non-uniformly, how do we know that this is not part of some kind of cycle? How do we not know that maybe the galaxies are orbiting a super-ginormous (holy _ _ _ -) super black hole? or orbiting a bunch really gigantic super black holes that are placed in a very strange geometric position? How do we know that things moving away from us at NOT the same rate, are due to an expansion and not something else? I know "the expanding universe" is just a theory, but it seems at this day and age, to accepted as fact. But how sure are we that this theory is, in fact, a fact?

    May I also remind the community that those fantastic telescopes are also not fully accurate. Light can only travel so far in a given time. It is possible that the light we sent out has not yet traveled to those things in the universe that are not moving away from us. Is it possible that the light from those telescopes gets deflected somehow and as a result takes longer to reach certain areas, resulting in a belief that things are getting further away from us, and the end result belief, that the universe is expanding? How are we sure that maybe aliens are not sitting in space with a strange gigantic invisible mirror that in-cases the earth, that sends light that we send out to rooms, where aliens upload images for us to think we are seeing? or whatever?

    ...Okay, I think that's enough argument from me; I think you get my point. What say you Physics forums?

    What are you thoughts about this? Am I a complete idiot? Is there no logic in my statement(s)? Have I understood something incorrectly? Did I say something that is wrong or incorrect? Do you agree with something?

    Please share your thoughts! I'd like to hear what you guys think; I would like to be proven wrong, just for the sake of curiosity. I am awaiting your replies...:smile:

    Thank you for reading,
  2. jcsd
  3. Dec 3, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Last edited by a moderator: May 6, 2017
  4. Dec 3, 2012 #3
    Go to YouTube and watch the first 20 minutes of Cosmology Lecture 1 by Susskind.

    Covers this exact question very nicely.
  5. Dec 3, 2012 #4

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    You might want to take that chip off your shoulder. It will interfere with your learning process.

    For example, telescopes do not work by shining light on distant objects. Stars produce their own light, which is collected by the telescope.
  6. Dec 3, 2012 #5


    User Avatar
    Science Advisor

    Your example makes no sense. How can the cars move apart if they are going at the same speed?

    Here's a better example. An endless stream of cars- each one goes 1mph faster than the one behind it. Clearly, the distance between each car will grow at 1mph and no matter which car you are in, you see every car moving away from you.
  7. Dec 3, 2012 #6
    What a preposterous way to paint physicists and astronomers. "Astronomy knowing creatures" wouldn't say such a thing. Virtually no scientist would.
  8. Dec 3, 2012 #7


    User Avatar
    Homework Helper

    How about 3 cars in on an imaginary endless flat plane (so not the earth). Car 1 goes north, car 2 goes east, car 3 goes south, all at the same speed if you want. You can consider car 2 to be the center of this virtual 3 car universe. Over time, the distances between the cars will continue to grow.

    The other posts in this thread include links to articles or discussions why there is observable evidence that the universe is expanding.
  9. Dec 3, 2012 #8


    User Avatar
    Staff Emeritus
    Science Advisor

    I didn't notice this at first but I want to point out a few issues.

    First, as has been mentioned already, is that telescopes do NOT send light out. The lens or mirrors of a telescope merely focus light that comes into them. Your eyeball does the same thing. A light bulb is hot enough to emit visible light which is reflected off of everything in your room and into your eye, where it is focused on your retina and absorbed, leading to vision.

    Second, your sense of scale of space is WAAAY off. Space is big. REALLLY big. HUGELY big. Light moves at 186 THOUSAND miles per SECOND. That's 7 and a half trips around the Earth per second. And it still takes light 8 minutes to get here from the Sun. The nearest star is 4 LIGHT YEARS away. That's 4 YEARS of travel time ONE WAY for light to get here from the nearest star, or for any light or other EM waves to get to that star from us. The nearest major galaxy, the Andromeda Galaxy is 2 MILLION light years away. We can see about 40 billion light years out, which after accounting for the increase in size of the observable universe due to expansion corresponds to about 13 billion years of travel time.
  10. Dec 3, 2012 #9
    @Drakkith: Thank you for replying! You're absolutely right about light. I can't believe I said something that is a semi- opposite of what actually happens. Sometimes I wonder how information which is nicely stored in my brain, becomes jello when I try and explain things (mus be all those advertisments on TV just messing around in my head, haha). I admit I was fully wrong here. Light comes from things far away from us, and is then collected by us with our telescopes. I have no idea how I could have said such a mistake....I am an idiot, lol. Thank you for your correction. I don't think ill make that kind of mistake again. Also, thank you for the links; the one that made the biggest impact on me was the balloon analogy one. I now understand that as the universe expands, it is literally pushing everything in different directions, spreading each object out, just like the air in the balloon: each "original" piece of air gets further away from another, just like the objects in the universe. Thanks again.

    @the_emi_guy: Thanks for posting, but I already found my answer. Thank you though.

    @Vanadium 50: As I said to Drakkith, I have no idea how I could make this kind of mistake, but again, thank you for correcting me.

    @ModusPwnd: Okay, this is what happens when I try putting humor in my posts...no one gets it, lol. You should really not "nit-pick" at posts, as this does not help the topic in anyway and wastes times, but yes, you're right. I was going a bit to far in making fun of the recent gloating- nature of mankind. Thanks.

    @Khashishi and rcgldr: You guys clearly did not understand my analogy. And that's no problem, I don't think anyone understood it, lol. I was trying to say that if you have cars moving at the same speed, then the distance between them should not change. And if the universe expands at the same rate, then the distance between the objects in it, should not change either. However, I see how that analogy is wrong now... thanks though.

    Thanks again everyone, feel free to lock this topic down; I got my answer. Again thanks.

  11. Dec 4, 2012 #10
    the doppler effect causes wavelengths of any wave to increase (equivalently, frequency to decrease) for a source moving away from the receiver. we are the receiver here. light is an electromagnetic wave; you can prove it with a diffraction experiment that it indeed behaves as a wave.

    it turns out that when we look at light sources from far away, they display redshift. let me explain what this means. why do we say something has redshifted light? how do we know its light was simply not emitted at a lower frequency?

    this gets you into some basic chemistry from high school. we know for a fact that atoms have definite energy levels. these energy levels arise from definite different states of electrons in atoms.

    when states change, energy is either given off or absorbed. sometimes this is in the form of heat - this often happens in solids and liquids. but in gases and plasmas, which make up 99.9999% of the visible mass of the universe, energy is given off as electromagnetic waves.

    these electromagnetic waves, or light, are emitted at a given frequency that is characteristic of the atom involved, the transition's beginning and end states and nothing else. also, all atoms of one element are identical; you cannot distinguish one hydrogen atom from another, so all hydrogens will have the same transitions.

    however for far away objects a peculiar thing happens. you notice that the transition wavelengths are longer for these far away objects than for the same process on earth; indeed, though their relative energy differences from each other stay the same (so we know its the same substance), all their frequencies are shifted down. this means that they're moving away.

    But you look in any direction and everything shows this redshift, the further away they are, the more redshifted. If this does not show expansion in all directions, what else could possibly explain it?
  12. Dec 5, 2012 #11
    There are more than 1 type of red-shift which is gravitational red-shift, cosmological red-shift, and Doppler red-shift. The cause of the expansion of the universe is unknown while there are models other than the big bang that can still explain the red-shift, but you'll look into the big bang as the most plausible theory yet to date, although you can't still rule out other possibilities which explains our universe. Dark energy is just nothing more than a placeholder for now. Could the red-shift be partly intrinsic? Maybe, but not enough to explain everything. As far as the static universe goes, there's the exchanges of graviton and photon idea, but there isn't any convincing evidence to suggest it. Nothing wrong with taking a look at them though.
    Last edited: Dec 5, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook