# Are we at the center of the universe and whats at the edge?

• YoungDreamer
In summary, the conversation covers various questions and theories about the size and nature of the universe. Topics include the concept of a center of the universe, the possibility of multiple big bangs, the limitations of our technology in observing the universe, and the properties of the edge of the observable universe. The conversation also touches on the expansion of the universe and the potential for light beyond the observable horizon.
YoungDreamer
I am wondering about the size of the universe. I have read that we can only "see" 13.7 billion light years away in all directions and that we are in the center.
To my mind this presents a problem. The problem is what are the odds that we are in the center of the universe?
Then again even with astronomical odds...
But I have always assumed since I was younger that the universe went on forever and our observable universe was caused by a big bang, and that other big bangs could be going on septillions of light years away.
Is that a current theory or am I just dreaming.
And second.
Could it be possible that our technology is only capable of seeing exactly 13.7 billion light years away for whatever reason. Not because that is where the CMB is found, but assume that the matter in our universe goes on for 20 billion light years and if our technology could only see 13.7 billion light years away it would sweep around looking that far back in all direction and we would appear to be at the center. I don't know if I have explained my question well enough, I hope that you will get my point.
One last question.
What would happen if we took a spacecraft to the edge of our observable universe and just kept going.(I know we can't do that.) Would the gravity of the entire universe stop us from moving further. Or would we loop around or just go on into complete darkness?
Thank You

The edge (as referred to in the title of the thread) of the *observable* universe is simply the distance from which light has had time to travel since the big bang. Nothing physical happens there. There is no physical edge : http://www.astro.ucla.edu/~wright/cosmology_faq.html#XIN

YoungDreamer said:
The problem is what are the odds that we are in the center of the universe?
There is no center. We have a FAQ on this: https://www.physicsforums.com/showthread.php?t=506991

YoungDreamer said:
But I have always assumed since I was younger that the universe went on forever

YoungDreamer said:
and our observable universe was caused by a big bang, and that other big bangs could be going on septillions of light years away.
The big bang is not an explosion that happened at a point in a preexisting empty space (see the first FAQ above). Therefore it doesn't make sense to imagine multiple explosions happening at different points in preexisting empty space.

YoungDreamer said:
Is that a current theory or am I just dreaming.
Current theory is as described in the second FAQ above. Either the universe is infinite and has always been infinite, or it's closed and has always been closed. Either way, there is no physical edge, and no empty space into which matter is expanding.
YoungDreamer said:
Could it be possible that our technology is only capable of seeing exactly 13.7 billion light years away for whatever reason.
The edge of the observable universe isn't set by technology, it's set by the distance that light has had time to travel since the big bang. The radius of the observable universe is actually about 46 billion light years, not 13.7: https://www.physicsforums.com/showthread.php?t=506987

YoungDreamer said:
Not because that is where the CMB is found, but assume that the matter in our universe goes on for 20 billion light years and if our technology could only see 13.7 billion light years away it would sweep around looking that far back in all direction and we would appear to be at the center. I don't know if I have explained my question well enough, I hope that you will get my point.
Current cosmological models do not allow light to "wrap around" like this, even if the universe is closed. If it's closed, and light sets off around its circumference, it will never get all the way around, because the circumference is expanding in the meantime.

YoungDreamer said:
One last question.
What would happen if we took a spacecraft to the edge of our observable universe and just kept going.(I know we can't do that.) Would the gravity of the entire universe stop us from moving further. Or would we loop around or just go on into complete darkness?
Nothing special happens there. It has the same properties as any other place in the universe. By the time a spacecraft got there, at a fraction of the speed of light, the edge of the observable universe as seen from Earth wouldn't be there anymore. It would be farther out. We can expand our knowledge of the observable universe far more rapidly just by waiting than we could by sending probes. Every year, the observable universe's radius increases by several light-years, both because light has more time to travel and because space is expanding.

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So then the fact the universe is ever expanding combined with the fact that the light has now traveled further points right to the answers of the universes size and can be confirmed constantly?

Shouldn't say "points right to the answers of the universes size" but should have said
Show the telltale signs of the universes size.

Sorry, I'm not quite following what you're asking in #3 and #4.

Hi Ben, YD,

I recall around 10 days ago YD started a thread with a related question. We tried to answer in that other thread. As I recall, I didn't do a very good job on that one. Pitched it at the wrong level or something, so it didn't take.

YoungDreamer said:
I have a question sort of related the size of the observable universe.

I know that we are limited by the speed of light in how far we can see, but what I am wondering is...

In the early universe when the first light could finally break free and travel in straight lines did it travel in all directions like the light given off by a star, and if so could there be light 13.7 billion light years beyond the horizon and we just can't see it because there is nothing to reflect it back to us?

Would this have any importance or relevance of any kind?

And is 13.7 billion light years the distance across the entire universe or just from our position outwards in all directions, making the universe around 28 billion light years across?

Hello marcus, I'm glad you reminded me of that post.
For some reason no matter how much I read and think I just can't seem to see the universe in the way you do. The only other thing that gives me such trouble understanding is black holes. I am not a scientist of any sort but I have always had a deep yearning to understand the universe, so I do a lot of reading on the subject. Obviously I know relatively little about the universe but the ideas and theories seem to be logical and I have a general sense of understanding of things.

However I am still trying to understand the "edge" of the universe. It always changes distance because it is constantly moving away. But if we could somehow travel to the farthest known point in the universe and pulled right up beside the last piece of matter or light and then, traveling in the same direction the universe is expanding what if we suddenly accelerated to light speed.
I know that's a lot of extreme hypotheticals but its how I make sense of things. I visualize going there. Probably why I can't make sense of black holes.
Anyways if we approached the the edge of the universe at light speed once we were passing that boundry, because obviously you would have to pass all the matter that is traveling at less than light speed, would space just be created and no matter how far you went it would always just be encompassed by our observible universe therefore always being a part of our universe and never being "outside" of our universe to begin with?

I hope I'm on the right track or that someone can refer me to a good article somewhere.

OK after reading a little more maybe I shoule be saying that we would need to travel 45 billion years not 14 billion years?
Not the look back time but proper distance?
But other than that error my question remains the same.

Or maybe it will be easier to answer if I use my scenario from the other post.

If there is a star close to the edge of the universe and its light is reaching us, it must be shining light at least the same distance in the opposite direction, the direction of the edge of the universe.
Since the light is moving away from us we cannot see it but wouldn't the light still occupy spacetime past the observable universe.

YD, the most basic principle in standard cosmo is called the Cosmological Principle. Matter and space are coextensive. Matter is evenly distributed throughtout all space (roughy speaking on average). Of course the matter is locally clumped and clustered into galaxies and such, but at a larger scale assume it averages out to be even.

If space is infinite then there is an infinite amount of matter, because it is uniformly evenly spread throughout.

If space is finite then there is a finite amount of matter. They are co-extensive.

That is the first rule. I guess it goes back to Einstein around 1920 give or take a few years. To begin to understand you have to teach your mind to picture like that: no big spaces without matter, no matter without space. Later you might come to explore ways of breaking that rule, or testing it, or challenging it. But that is the first step in understanding.

How are you with that? Can you for starters assimilate the Cosmological Principle? Make it a rule to think of the universe that way?

One way of saying this ( http://en.wikipedia.org/wiki/Cosmological_principle ) is that REGARDLESS OF WHERE YOU ARE IN SPACE THINGS LOOK APPROXIMATELY THE SAME as they do here or anywhere else, averaged over large enough scale so individual shapes of galaxies get washed out.

If you think this way, no "edge" or "boundary" is imaginable. Such a thing would contradict the main working assumption we all share---the cosmo principle. Because at an edge things would look different.

Have you watched the Wright balloon model? If not, try it. there is a 2D universe with no edges. It meets the requirements of the Cosmo Principle. Google "wright balloon model" and see if you get it.

I'm assuming you WANT to get so you can think enough like a professional cosmologist that you can understand the basics of what they're are talking about.

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Ok the way I have been thinking of it is space existed and the big bang created matter into the space and has just been filling an increasing volume of space as it expands but the space it is expanding in is infinite.

I know that is not the way the current models work.

Am I too understand it like this, as the universe expands larger and larger it is creating more spacetime, and even if something were to travel past the furthest matter it would still be a part of this universe so there can never be an outside of the universe.

Ok the way I have been thinking of it is space existed and the big bang created matter into the space and has just been filling an increasing volume of space as it expands but the space it is expanding in is infinite.

I know that is not the way the current models work.

Am I too understand it like this, as the universe expands larger and larger it is creating more spacetime, and even if something were to travel past the furthest matter it would still be a part of this universe so there can never be an outside of the universe.

YoungDreamer said:
Ok the way I have been thinking of it is space existed and the big bang created matter into the space and has just been filling an increasing volume of space as it expands but the space it is expanding in is infinite.
...

That is your trouble! It is the "explosion" misconception. It is one of the common misconceptions people have.

There is a Scientific American article called "Misconceptions about the Big Bang" that is often recommended. But the main thing is you have to WANT to get over it.

If you want to cling to the "explosion" picture of matter exploding out into empty space then it is very hard to communicate.

I have the SciAm article in my signature, it is the "charley" link. the first page is blank so scroll down
=======

The explosion model would give an inferior fit to the observational data, and runs counter to the spirit of our presentday law of gravity, which is Einstein 1915 relativity.

It is more or less useless to try to proceed if you are hung up on thinking of the universe as infinite empty space with an explosion of matter in it.

I'm off to bed. Maybe I;ll see you tomorrow.

bcrowell said:
There is no center. We have a FAQ on this: https://www.physicsforums.com/showthread.php?t=506991

"We can visualize this using the metaphor in which galaxies are dots on a balloon being blown up. No point on the balloon is the center of expansion. If you want to pick out a center, you have to pick a point in the air, not on the surface of the balloon. But in the balloon analogy, the third dimension is just an aid to visualization. Only points on the balloon's two-dimensional surface represent actual points in space."

No center in space, yes.
But can't we say that the Universe has a center in time - the Big Bang in the center of the balloon, and that the surface of the balloon is the present time, the air is the past and outside the surface of the balloon is the future which does not yet exist?

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Marcus I absolutely want to shed any misconceptions I have, that is why I'm here.
I know you are not suggesting otherwise.
I think that I have thought the same way for too long and it is just hard relearning such a complex thing that isn't even understood in the first place.
I feel that if I don't look at the universe for what the facts say it is then I am not really looking at it at all.
So...
I have re-read the balloon analogy, I feel that the balloon analogy is good for explaining the idea of the Hubble Constant and how the universe expands but how can I view a 2-D object and get a sense of a 3-D universe?
Or is the balloon analogy not going to do that.
So...
Here is my revised view, correct me where I'm still not seeing it the right way.
The BB started as a singularity, a very mysterious thing that I won't get into cause I really really don't understand that. The BB wasnt really a bang it was an expansion. And it keeps expanding at an ever increasing rate. It is like a 3-D spherical cobweb stretching out in all directions. And there is never an edge because there is no outside of the universe just like there was no outside of the singularity that created all matter.

"To begin to understand we must first understand that we may never understand"

Octavianus said:
But can't we say that the Universe has a center in time - the Big Bang in the center of the balloon, and that the surface of the balloon is the present time, the air is the past and outside the surface of the balloon is the future which does not yet exist?

In cosmological models constructed using GR, spacetime only exists for t>0. There was never a t=0.

(The other thing to point out is that the balloon metaphor only works for a closed universe. If the universe is open, then you want to visualize it as an infinite rubber sheet.)

Marcus will do much better than I could for theories like LQG that have a bounce rather than a bang, but I think in those cases you would have a time coordinate that is like the real line, with a temporal "center" at t=0. But I believe the universe has nonzero spatial size at the bounce, so there is still no spatial center.

YoungDreamer said:
Am I too understand it like this, as the universe expands larger and larger it is creating more spacetime, and even if something were to travel past the furthest matter it would still be a part of this universe so there can never be an outside of the universe.

When you say "past the furthest matter," it sounds like you're still imagining matter exploding into a preexisting vacuum. Try the balloon metaphor for the case of a closed universe. The farthest matter is at the opposite side of the balloon. If you go past it, you're just coming back closer to home again.

Octavianus said:
"We can visualize this using the metaphor in which galaxies are dots on a balloon being blown up. No point on the balloon is the center of expansion. If you want to pick out a center, you have to pick a point in the air, not on the surface of the balloon. But in the balloon analogy, the third dimension is just an aid to visualization. Only points on the balloon's two-dimensional surface represent actual points in space."

No center in space, yes.
But can't we say that the Universe has a center in time - the Big Bang in the center of the balloon, and that the surface of the balloon is the present time, the air is the past and outside the surface of the balloon is the future which does not yet exist?

I think that is an ingenious way to think about it. It's one possible way. If you find that way of picturing spacetime appealing and useful you are not alone.
As a 3D creature used to thinking geometrically in no more than 3D, I don't know of any perfect way of intuiting spacetime. It's probably good to have several mental images, analogies, you have learned how to use as helps, and not get rigidly bound to one mental picture.

You are talking about using radial distance in 3D as a time-coordinate in picturing 3D spacetime. (And then as always there is the everpresent problem of trying to go from the analogy up to one higher dimension.)

bcrowell said:
... theories like LQG that have a bounce rather than a bang, but I think in those cases you would have a time coordinate that is like the real line, with a temporal "center" at t=0. But I believe the universe has nonzero spatial size at the bounce, so there is still no spatial center.

Yes! that is one problem with Octavianus' proposal of a mental aid in imagining time. I didn't want to mention it because one can only go step by step in learning. Radial time is not a "final solution" analogy.

As you suggest, there are some models where there is a bounce, as if the balloon has been collapsing for a long long time, gets down to a minimum size, and then "rebounds" and starts expanding again. In that picture there is no idea of a "beginning" to existence. One just has to accept that existence exists---time does not have a first moment.

I would be happy if Octavianus did not worry about that right now (it does not fit the radial time visuaiization strategy... because radial time is only one sided infinite. It is only infinite in one direction, so it can't handle everything we might want to do with spacetime.

So would I be correct to say that the universe is like the Earth to an ant
Bear with me...
An ant could crawl around on the Earth forever and never reach an edge.
Is that how the universe as a whole works, if we went as far as we could go we would be back where we started?

Eventually i'll begin to understand.

Ok I take back what I said about ending up where you started because the universe is expanding and more space is being made in front of us and you can't get to the edge of something that has a constantly moving edge.

YoungDreamer said:
Ok I take back what I said about ending up where you started because the universe is expanding and more space is being made in front of us and you can't get to the edge of something that has a constantly moving edge.

We also don't know whether the universe is closed (like a sphere) or open (like an infinite plane): https://www.physicsforums.com/showthread.php?t=506986

The Big Bang disproved that we are at the center of the universe. The European Space Agency on July 5, 2010 had a article "Planck unveils the Universe – now and then" that I think is helpful to this discussion:

ESA PR-15 2010 ESA’s Planck mission has delivered its first all-sky image. It not only provides new insight into the way stars and galaxies form but also tells us how the Universe itself came to life after the Big Bang.

“This is the moment that Planck was conceived for,” says ESA Director of Science and Robotic Exploration, David Southwood. “We’re not giving the answer. We are opening the door to an Eldorado where scientists can seek the nuggets that will lead to deeper understanding of how our Universe came to be and how it works now. The image itself and its remarkable quality is a tribute to the engineers who built and have operated Planck. Now the scientific harvest must begin.”

From the closest portions of the Milky Way to the furthest reaches of space and time, the new all-sky Planck image is an extraordinary treasure chest of new data for astronomers.

The main disc of our Galaxy runs across the centre of the image. Immediately striking are the streamers of cold dust reaching above and below the Milky Way. This galactic web is where new stars are being formed, and Planck has found many locations where individual stars are edging toward birth or just beginning their cycle of development.

Less spectacular but perhaps more intriguing is the mottled backdrop at the top and bottom. This is the ‘cosmic microwave background radiation’ (CMBR). It is the oldest light in the Universe, the remains of the fireball out of which our Universe sprang into existence 13.7 billion years ago.

While the Milky Way shows us what the local Universe looks like now, those microwaves show us what the Universe looked like close to its time of creation, before there were stars or galaxies. Here we come to the heart of Planck’s mission to decode what happened in that primordial Universe from the pattern of the mottled backdrop.

The microwave pattern is the cosmic blueprint from which today’s clusters and superclusters of galaxies were built. The different colours represent minute differences in the temperature and density of matter across the sky. Somehow these small irregularities evolved into denser regions that became the galaxies of today.

The CMBR covers the entire sky but most of it is hidden in this image by the Milky Way’s emission, which must be digitally removed from the final data in order to see the microwave background in its entirety.

When this work is completed, Planck will show us the most precise picture of the microwave background ever obtained. The big question will be whether the data will reveal the cosmic signature of the primordial period called inflation. This era is postulated to have taken place just after the Big Bang and resulted in the Universe expanding enormously in size over an extremely short period.

http://www.esa.int/esaCP/SEMF2FRZ5BG_index_0.html

A propos this quote by ViewsofMars about the ESA Planck mission, an earlier Planck mission webpage had this rather poetical "rabbit on the moon" description of the sensitivity with which it is mapping the Ancient Light.

Like measuring the heat of a rabbit on the Moon

The detectors will look for variations in the temperature of the CMB that are about a million times smaller than one degree – this is comparable to measuring from Earth the heat produced by a rabbit sitting on the Moon. This is why the detectors must be cooled to temperatures close to absolute zero...​
http://www.esa.int/esaCP/SEM0Y5S7NWF_index_0.html

I don't know how the ESA tech writers came up with that, or even if it is physically accurate, but I thought it was charming, and had a slight gallic flavor. It seemed somehow right for someone thinking in French to describe a quantity of heat radiation as the amount received by us from one rabbit situated on the moon.

YoungDreamer said:
An ant could crawl around on the Earth forever and never reach an edge.
Is that how the universe as a whole works, if we went as far as we could go we would be back where we started?

That sounds right, YD, and as you later pointed out you would have to imagine stopping the expansion process in order to make it around.

But that's all right. It is OK to imagine distances with expansion stopped, so that you have time to measure or travel and they don't change while you are doing that. It helps understand the geometry.

The distance between two things that you would measure if you could stop expansion at a certain moment is called the "proper distance" at that moment. It's a technical term---in a universe with dynamically changing geometry there can be several different types or definitions of distance, this is one of the most commonly used.

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Didnt think rabbits ate cheese. Perhaps a large mouse?

Hey, thanks Marcus! (I'm writing a poem about you.) Adding a tad more to this subject. Picking up where I left off. From European Space Agency:

Planck’s new view of the cosmic theatre

11 January 2011
ESA PR-3 2011 The first scientific results from ESA’s Planck mission were released at a press briefing today in Paris. The findings focus on the coldest objects in the Universe, from within our Galaxy to the distant reaches of space.

If William Shakespeare were an astronomer living today, he might write that “All the Universe is a stage, and all the galaxies merely players.” Planck is bringing us new views of both the stage and players, revealing the drama of the evolution of our Universe.

Following the publication by ESA of the first full-sky Planck image in July last year, today sees the release of the first scientific results from the mission.

These results are being presented by the Planck Collaboration at a major scientific conference in Paris this week, based on 25 papers submitted to the journal Astronomy & Astrophysics.

Planck investigates the cosmic infrared background

The basis of many of these results is the Planck mission’s ‘Early Release Compact Source Catalogue’, the equivalent of a cast list.

Drawn from Planck’s continuing survey of the entire sky at millimetre and submillimetre wavelengths, the catalogue contains thousands of very cold, individual sources which the scientific community is now free to explore.

“This is a great moment for Planck. Until now, everything has been about collecting data and showing off their potential. Now, at last, we can begin the discoveries,” says Jan Tauber, ESA Project Scientist for Planck.

We can think of the Universe as a stage on which the great cosmic drama plays out over three acts.

Visible-light telescopes see little more than the final act: the tapestry of galaxies around us. But by making measurements at wavelengths between the infrared and radio, Planck is able to work back in time and show us the preceding two acts. The results released today contain important new information about the middle act, when the galaxies were being assembled.

Planck shows galaxy formation taking place
Planck has found evidence for an otherwise invisible population of galaxies shrouded in dust billions of years in the past, which formed stars at rates some 10–1000 times higher than we see in our own Galaxy today.

Measurements of this population had never been made at these wavelengths before. “This is a first step, we are just learning how to work with these data and extract the most information,” says Jean-Loup Puget, CNRS-Université Paris Sud, Orsay, France.

Eventually, Planck will show us the best views yet of the Universe’s first act: the formation of the first large-scale structures in the Universe, where the galaxies were later born. These structures are traced by the cosmic microwave background radiation, released just 380 000 years after the Big Bang, as the Universe was cooling.

However, in order to see it properly, contaminating emission from a whole host of foreground sources must first be removed. These include the individual objects contained in the Early Release Compact Source Catalogue, as well as various sources of diffuse emission.

Planck zeros in on anomalous emission in Rho Ophiucus
Today, an important step towards removing this contamination was also announced. The ‘anomalous microwave emission’ is a diffuse glow most strongly associated with the dense, dusty regions of our Galaxy, but its origin has been a puzzle for decades.

However, data collected across Planck’s unprecedented wide wavelength range confirm the theory that it is coming from dust grains set spinning at several tens of billion times a second by collisions with either fast-moving atoms or packets of ultraviolet light.

This new understanding helps to remove this local microwave ‘fog’ from the Planck data with greater precision, leaving the cosmic microwave background untouched.

“This is a great result made possible by the exceptional quality of the Planck data,” says Clive Dickinson, University of Manchester, UK.

http://www.esa.int/esaCP/SEMK4D3SNIG_index_0.html

What does ESA do?

ESA’s job is to draw up the European space programme and carry it through. ESA's programmes are designed to find out more about Earth, its immediate space environment, our Solar System and the Universe, as well as to develop satellite-based technologies and services, and to promote European industries. ESA also works closely with space organisations outside Europe.

## What is the current understanding of the center of the universe?

The current understanding is that there is no specific center of the universe. The universe is constantly expanding in all directions, making it impossible to determine a single central point.

## How do scientists study the edge of the universe?

Scientists study the edge of the universe by observing distant galaxies and measuring their redshift, which gives information about the expansion rate of the universe. They also use telescopes and other instruments to study the cosmic microwave background radiation, which is the leftover radiation from the Big Bang.

## Is there a physical boundary at the edge of the universe?

There is no physical boundary at the edge of the universe. The universe is believed to be infinite and constantly expanding, with no defined end or edge.

## Are there other universes beyond the edge of our observable universe?

While it is a popular theory, there is currently no scientific evidence to support the existence of other universes beyond our observable universe. However, this is an area of ongoing research and exploration in the field of cosmology.

## Can we ever know for sure if we are at the center of the universe?

It is unlikely that we will ever be able to determine for sure if we are at the center of the universe. Our understanding of the universe is constantly evolving and expanding, and it is possible that our current understanding may change in the future. Additionally, the concept of a single, stationary center of the universe may not even be applicable in the vastness of the cosmos.

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