Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 26/09/2016 17:55:25
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This week Brian Lucas wanted to know: where are we within the universe? Joanna Kerr decided to try and find out with help from Dr Sean McGee, an astrophysicist from the University of Birmingham.
Listen to this Show (http://www.thenakedscientists.com/HTML/podcasts/qotw/show/20150818/)
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If you want to discuss this show, or ask a question, this is the place to do it.
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Because there is no center and no observable edge to the universe, we will need a reference point. How about the Earth as a reference point? For all intents and purposes, it is the "center" of the observable universe for us earthlings. Therefore, we are located at the following address: Earth, Solar System, Orion Arm, Milky Way galaxy, local galactic group, Virgo Supercluster, Laniakea Supercluster, Observable Universe, Universe. The location can be further defined if necessary. The minimum diameter of the observable universe is 28,000 megaparsecs and the universe appears the same in all directions. My guess is that there is a lot more out there, but the light either has not reached us yet or the universe is expanding faster than the speed of light at distances greater than 14,000 Mpc.
Another poor analogy is to consider dots on the surface of an expanding balloon. How do you define the location if there is only one dot and the surface of balloon is all that exists? You can't, unless there are other dots to reference. With more dots we can identify the location and apparent movement of one dot relative to other dots at a given moment in time.
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As the universe appears from here to be fairly isotropic and populated with sparse random dots of matter, it seems that we are at the centre. As we have no reason to believe that our position is in any way special, it is equally true that any other point can be considered to be the centre.
Alternatively you could imagine an "actual" universe considerably larger than the observable universe, in which case any point within the observable universe would be the centre of the observable universe.
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This often asked question never gets an answer acceptable to either the layman or common sense.
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The universe is centered on me... you're off to one side.
[;)]
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This often asked question never gets an answer acceptable to either the layman or common sense.
Try this for a layman common sense answer;
As the Universe is all that is, and according to current popular consensus, at the moment of the Big Bang there was no space to separate anything from anything else, then everything that is, is still where it was then. Everything is now separated from everything else by ever increasing amounts of space but it is still where it was then.
Nothing has moved.
If all the space that has come into existence since the Big Bang was to suddenly disappear, Everything would again not have any separation from everything else, just like before.
That means that every fundamental particle in the entire Universe, is, was, and ever will be at the centre of the Universe.
Hope that helps...
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Are you saying then that everything that exists now in the universe existed at the first moment of the big bang? And that at that moment it had no size?
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Are you saying then that everything that exists now in the universe existed at the first moment of the big bang? And that at that moment it had no size?
Ron I am saying that at the moment that our science can operate, is when Timespace/Spacetime started.
As there can not be a before without Time, there also can not be size without Space.
There was if "was" can be used, no space to separate anything from anything.
Science starts at the coming together of the Matter/Energy (us) part of the Universe with Spacetime.
At this frame of reference, (the first) the Universe is already Huge. Every representative fundamental particle is separated by one Planck length of spacetime.
So yes the total amount of Mass/Energy that exists now existed at that first moment, and has been conserved ever since. It can not be created or destroyed.
Let's not be so Matter-centric though. Matter/Energy alone can not form a Universe. If it can exist in any sense of the word, it's not an existence we have any way to address.
To exist and be animate it needs Space to move.
Spacetime is something. It is not nothing. It has describable characteristics and is easily detected.
And being the means to an animated Universe, it is what we and everything are made of.
We are made of Space with a sprinkling of Stardust to give structure
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I understand that the universe came into existence after 10^-43 seconds (Planck time) when everything was separated by one Planck length. Space moved over the next Planck second and some separation took place. Here is where I have a problem, my reference to common sense if you like. One particle did not move relative to the others, the one at the centre. Or are you saying that everything moved away from any (possibly undefineable) centre and there is just a hole there, like the balloon analogy?
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Neither Ron. That's the beauty of it. No particle moved.
Because Space and Time are the same thing, with every planck unit of time after the first, there was another Planck unit of Space now separating each and every particle.
The particles themselves did not have to do any movement for this to happen.
Just like today.
It's not the galaxies moving apart.
They are being further separated by the creation of more spacetime between them.
The initial fundamental particles would have their angular momentum in their spin. Apart from that they stay exactly where they are, and the creation of more distance happens planck time after planck time.
The more time that passes the further an observer can look into the past. The limited speed of light translates that into a distance.
So you see Everything is still where it was then. The only thing that has changed is how much timespace has now existed.
The Universe is expanding into the future. Greater separation distances is just a side effect of Timespace.
Matter and Energy are conserved.
Time is not. It just keeps going forward. For every tick of any conceivable clock in any conceivable reference frame, we have proportionately more Space.
Do you see the beautiful symmetry of it all?
And notice there was no need for a Dark anything in the explanation. It's pure geometry.
It's like the expanding balloon analogy. I have heard so many people ask "But what is inside the Balloon?" or the opposite "What is outside the Balloon?"
That is simple; inside the balloon is the past. It's where everything was. And the outside, is where Everything will be when the balloon has expanded into that time. Every dot on the balloon from past to future remains stationary but ends up with more "Timespace/Spacetime" separating it from every other dot.
Sorry I get carried away sometimes...
Hope all this raving on my part hasn't confused you.
Given all this Timespace to play in we do have some movement, but on the large scales this is negligible.
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Thank you, I do get your explanation. One last question though. Taking the balloon analogy, there is no centre to it's surface but it does have a centre in three dimensions. That could mean that if you include the timeline (arrow of time of the universe?), there is a centre, that of the space that has expanded. Probably not traceable though or of any particular import.
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Ron, Any analogy can only carry an explanation so far. In the Balloon analogy the Balloon surface represents everything that is, was and ever will be.
You have to imagine the balloon doing something that balloons can't.
That is see the deflated balloon as all the surface shrinking evenly and maintaining it's shape as it is deflated. Rather than the limp wobbly thing that it does look like deflated.
So with that in mind, when it is totally deflated all the dots on it's surface are touching each other.
If we say the dots are elemental particles rather than the normal galaxies, we have the start of spacetime. The instant the first bit of air goes in, and the dots (our fundamental particles) have their first separation from each other.
None of them need to physically move from where they are.
The surface is a representation of the Universe's timeline. As it expands, it leaves the past behind. an observer can look into the centre of the balloon and see the past, but that same observer can only move in one direction in time. The expanding surface does not represent movement away from the physical centre of the Universe for any particle. Only movement in time. The extra space growing between the dots is a byproduct of "Time also being Space".
Another way that the balloon analogy fails is that we are considering the surface and the dots we see on it. We are therefore assuming a reference frame outside the Universe.
In reality there is no such reference frame. There is no outside the Universe.
In reality this surface is the Universe's timeline and not ours.
From the reference frame of any one of the dots, that view of the other dots is not available. No dot can look across the surface of the balloon. Because of the limited speed of light, the only direction viewable is towards the interior. (The past) Every dot can see where part of the surface of the balloon analogy was when the Universe was younger, but nothing can see the present in the present. Not even you reading this screen.
You see Ron, it is my opinion that because of our nature,(developed through evolving and surviving on the surface of a planet) we tend to think in material things, separated by Space. We have come to know that Time and Space are the same thing, but the Human mind tends to attach Time to Space as an add on and then promptly ignore it.
This very Human way of thinking leaves us asking questions like where does the Energy come from for this continuous Spacial Accelerated Expansion. We come up with misleading concepts like Dark Energy, because we can not see how more and more Space is always coming into existence. We ignore the Time component because we view it as an add on to Space. You will hardly ever see anyone referring to it as Timespace. Only as Spacetime. It's a subtle thing but it is important in that it directs our enormous imaginative and creative powers towards half the picture.
We are made of Timespace; with a sprinkling of Stardust..