Help a Physics Amateur - See Attachment!

[RhodesMedia]

Dear Physicists,

First time poster and a complete physics amateur with a serious question. I may not have posted correctly I just really want some help to understand something (I am not a crackpot!)...

My question is explained through diagrams please see the attachment.

I really appreciate any help!

 

[rcgldr]

Part of the reason is that the stars or any objects that create light didn't exist until they were separated by great distances.

 

[Cantstandit]

The way I see it, the classical laws of physics were always there, and did not "wait" for the laws of quantum physics to stop applying, they were just too "small" to matter, not unlike force gravity virtually does not apply to atoms.
And I think there is no centre of the universe per se. The space itself expanded so the centre is "everywhere".
Now instead of working I will be thinking about the beginning of space, time and matter ;)

 

[vanhees71]

It's also a misconception about the big bang, which is hard to imagine intuitively since it's not like an explosion in a given space, i.e., something expanding in space. It's the very creation of space-time itself out of a singularity. With the general theory of relativity, which is a classical relativistic field theory of a massless spin-1/2-field which can be reinterpreted as the space-time pseudometric of a pseudo-Riemannian manifold which makes up the four-dimensional space-time.

On a long-range scale, this space-time is homogeneous and isotropic, i.e., there is no exceptional point (particularly not something that you'd call a center) and not exceptional direction in space. More precisely formulated one should say, you can define a frame of reference, with respect to which each observer at rest sees a homogeneous and isotropic space. Due to this large symmetry, the corresponding space-times are mathematically classified in three types: closed (spherical), flat, open (hyperbolical). The space-times are named after their discoverers as Friedmann-Lemaitre-Robertson-Walker solutions of Einstein's field equation. The only function left to be calculated after choosing a fundamental frame of reference is a scale factor, which is a function of time. The particular solution of this function depends on the matter content, where matter is everything except gravitation, including according to the standard cosmological model usual (baryonic) matter, electromagnetic radiation, neutrinos (making only about 5% of the total matter content), dark matter made up of yet to be discovered unknown particles (about 20%) and the greatest mystery of all physics, dark energy (cosmological constant, about 75% of the matter content).

We have two main sources of information about the scale factor from the redshift of distant supernovae, which can be used as standard candles, and the high-precision measurement of the fulcutations of the cosmic microwave background radiation (CMBR) through satellites like COBE and WMAP. Recently the most precise instrument of this kind has been launched, the satellite PLANCK.

The CMBR is the relic radiation from the time where neutral atoms have formed from the charged atomic nuclei (mostly hydrogen and helium) and electrons floating around in the universe. This has been possible after about 400000 years after the big bang when the universe had cooled down below the socalled Mott-transition temperature, where the state of matter makes a phase transition from a plasma to a gas of neutral atoms. The plasma had been nearly in thermal equilibrium and as long as the particles of such a medium are charged, also the electromagnetic radiation is scattered around and thus in equilibrium with the medium. After the formation of a neutral gas, the radiation decouples. This means the spectrum of the radiation stays an equilibrium (Planck spectrum) at all times but becomes red shifted through the expansion of the scale factor, i.e., it becomes cooler. At the moment the temperature is about 2.7K and thus the maximum of the spectrum sits in the microwave region. The precise measurements of WMAP has revealed that the temperature fluctuates only with $\delta T/T \simeq 10^{-5}$. This makes the CMBR the most precise Planck spectrum ever measured! Nevertheless these tiny fluctuations can tell us about the state of the universe at recombination, i.e., 400000 years after the big bang. Together with the red-shift observables from supernovae (among other observations through the Hubble Space Telescope) these fluctuations tell us that our universe is flat to a high accuracy and that the expansion of the scale factor accelerates. This is only possible due to the large amount of dark energy in the universe since all normal matter acts decelerating since for normal matter gravity is always attractive.

We have no explanation for the amount of dark matter measured. It's one of the greatest enigmas of contemporary physics. Maybe the answer to this question is related with the so far unsolved theoretical problem to find a consistent quantum-theoretical description of gravitation (and most likely of space-time iteself).

 

[HallsofIvy]

The best thing to say about your question is that it is nonsense. We are NOT far from the center of the universe because there is NO center of the universe or point where the big bang occured. Space itself was created at the big bang- every point is the point where the big bang occured.

 

[Quinzio]

The way I see it, the classical laws of physics were always there, and did not "wait" for the laws of quantum physics to stop applying, they were just too "small" to matter, not unlike force gravity virtually does not apply to atoms.
And I think there is no centre of the universe per se. The space itself expanded so the centre is "everywhere".
Now instead of working I will be thinking about the beginning of space, time and matter ;)

For a good reason.
And there's no IN and OUT of the universe, because out of the universe, there's even no space and no time.
Now instead of sleeping, I'll try to understand how does it feel without space and time.

 

[RhodesMedia]

Guys,

Thank you so much for your replies. I especially was helped by "The space itself expanded so the centre is "everywhere"." and "Space itself was created at the big bang- every point is the point where the big bang occured."

Very helpful to show me how wrong my perception of the expansion was. Thanks.

But after reading the responses (vanhees71 just give me 354,567,324 more days to try to understand much of your response, but thanks very much!) and the other recommended threads regarding the centre (or rather lack thereof) of the universe i.e. https://www.physicsforums.com/showthread.php?t=496550 I am still left with my question. The thread states...

"any comparison of the Big Bang with an explosion in space is misleading. Rather, what we are talking about here is an expansion of space, which, according to the observations which have hitherto been made, seems to show us nothing which would correspond to a centre. You might want to take a look at the discussion found here...”

Which links to a page with an even better line...

“Yet there is no centre to the expansion; it is the same everywhere. The Big Bang should not be visualised as an ordinary explosion. The universe is not expanding out from a centre into space; rather, the whole universe is expanding and it is doing so equally at all places, as far as we can tell.”

So if space itself is what is expanding, wouldn't it still be congruous with the evidence that this very expansion of space is happening much faster than the speed of light?

Sorry that my understanding is so rudimentry guys...

 

[RhodesMedia]

Or is the fact we are able to "look back" at the light and appear to be in front of it... 'i.e. the light hasn't reached us yet... because, as rcgldr said, "the stars or any objects that create light didn't exist until they were separated by great distances."

This is totally logical... but is there something else at play?

From my understanding of the evidence it appears that space-time itself expands faster than light, hence, the speed of light isn't the 'fastest' thing there is.

 

[sicarius]

"So if space itself is what is expanding, wouldn't it still be congruous with the evidence that this very expansion of space is happening much faster than the speed of light?"

Assuming the expansion is uniform across the universe, then nearby objects would be moving away from you slower than those that are more distant. This is because there is more space to expand in between objects.

So, while this simple answer is "No, it is not expanding at the speed of light, since we do see light, it cannot be." A better explanation would be that there are still unanswered questions. Is the universe so large that the most distant parts are moving away faster than the speed of light? Possibly. Are there objects out there giving off light but are so distant that their light will never make it here? Maybe. If so, are there ways to detect them? Gravitational lensing could do it if a dense enough body is close enough to both us and the object, say half way in between, where it is only moving at 3/4 the speed of light away from each of us. Then the lensing effect would make it visible, where it's light would otherwise never reach us.

 

[Cosmo Novice]

Guys,

So if space itself is what is expanding, wouldn't it still be congruous with the evidence that this very expansion of space is happening much faster than the speed of light?

Ok I will try to explain this as I understand it.

The Big Bang (BB) was the beginning of the Universe (U). This was the beginning of time and space and led to the state where the laws of General Relativity (GR) apply. The BB did not begin in a pre-existing "space", this was the beginning everything including space and time. U can be defined as "the totality of everything that exists".

Generally time at the instant of the BB is reffered to as t=0. Science currently has no known theoretical proofs for this point in space/time. Quantum Mechanics is currently attempting unification of gravity with GR to theorise this point in space/time (if t=0 even exists). Science will talk about t>0, specifically t>1 Planck (a Planck is the smallest possible measurement of time).

In the early stages of U there was an inflationary period, in this period U was expanding much more rapidly than currently and many times the speed of light.

This expansion has continued, the expansion is not attributed to dark energy directly, however it is thought the increasing rate of expansion can be attributed to dark energy.

GR encompasses certain physical laws. One is that objects with mass cannot travel faster than c (light). Galaxies are receeding from us >c (faster than light). However this is not kinematic motion (some is actually kinemtaic motion but nothing close to c.) The reason they are receeding (notice i say receeding and not travelling) is that the space inbetween the galaxies is expanding.

So galaxies are receeding from us >c due to the rate of expansion of U, this does not in any way break the physical laws of GR, it is like a sidestep.

Cosmologists fit the best model to current observational data. Either the U will have an open or closed geometry, being then either spatially finite or spatially infinite depending on positive or negatice curvature - either way it has no spatial edge. If spatially flat then it is infinite in all directions, if curved either pos or neg then it is a higher dimensional manifold such as an n-sphere.

There is however an edge to the universe, and that is a temporal edge.

I hope this has helped clear this up for you a little. I am in no way a physicist or anything but have a good conceptual understanding of the current cosmological models.

 

[Cosmo Novice]

It's also a misconception about the big bang, which is hard to imagine intuitively since it's not like an explosion in a given space, i.e., something expanding in space. It's the very creation of space-time itself out of a singularity. With the general theory of relativity, which is a classical relativistic field theory of a massless spin-1/2-field which can be reinterpreted as the space-time pseudometric of a pseudo-Riemannian manifold which makes up the four-dimensional space-time.

On a long-range scale, this space-time is homogeneous and isotropic, i.e., there is no exceptional point (particularly not something that you'd call a center) and not exceptional direction in space. More precisely formulated one should say, you can define a frame of reference, with respect to which each observer at rest sees a homogeneous and isotropic space. Due to this large symmetry, the corresponding space-times are mathematically classified in three types: closed (spherical), flat, open (hyperbolical). The space-times are named after their discoverers as Friedmann-Lemaitre-Robertson-Walker solutions of Einstein's field equation. The only function left to be calculated after choosing a fundamental frame of reference is a scale factor, which is a function of time. The particular solution of this function depends on the matter content, where matter is everything except gravitation, including according to the standard cosmological model usual (baryonic) matter, electromagnetic radiation, neutrinos (making only about 5% of the total matter content), dark matter made up of yet to be discovered unknown particles (about 20%) and the greatest mystery of all physics, dark energy (cosmological constant, about 75% of the matter content).

We have two main sources of information about the scale factor from the redshift of distant supernovae, which can be used as standard candles, and the high-precision measurement of the fulcutations of the cosmic microwave background radiation (CMBR) through satellites like COBE and WMAP. Recently the most precise instrument of this kind has been launched, the satellite PLANCK.

The CMBR is the relic radiation from the time where neutral atoms have formed from the charged atomic nuclei (mostly hydrogen and helium) and electrons floating around in the universe. This has been possible after about 400000 years after the big bang when the universe had cooled down below the socalled Mott-transition temperature, where the state of matter makes a phase transition from a plasma to a gas of neutral atoms. The plasma had been nearly in thermal equilibrium and as long as the particles of such a medium are charged, also the electromagnetic radiation is scattered around and thus in equilibrium with the medium. After the formation of a neutral gas, the radiation decouples. This means the spectrum of the radiation stays an equilibrium (Planck spectrum) at all times but becomes red shifted through the expansion of the scale factor, i.e., it becomes cooler. At the moment the temperature is about 2.7K and thus the maximum of the spectrum sits in the microwave region. The precise measurements of WMAP has revealed that the temperature fluctuates only with $\delta T/T \simeq 10^{-5}$. This makes the CMBR the most precise Planck spectrum ever measured! Nevertheless these tiny fluctuations can tell us about the state of the universe at recombination, i.e., 400000 years after the big bang. Together with the red-shift observables from supernovae (among other observations through the Hubble Space Telescope) these fluctuations tell us that our universe is flat to a high accuracy and that the expansion of the scale factor accelerates. This is only possible due to the large amount of dark energy in the universe since all normal matter acts decelerating since for normal matter gravity is always attractive.

We have no explanation for the amount of dark matter measured. It's one of the greatest enigmas of contemporary physics. Maybe the answer to this question is related with the so far unsolved theoretical problem to find a consistent quantum-theoretical description of gravitation (and most likely of space-time iteself).

You should really keep your target audience in mind. Nice post though