brooksquest:

Jeff, if you could help alittle with where the Great Attractor is from the Milky Way.

It lies in the direction of the constellations Hydra and Centaurus. The giant galaxy cluster Abell 3627 is thought to lie near its core:

Our peculiar velocity in its direction is something like 600 or 700 km/sec.

... It would also be very helpful to know if the Great Attractor has any red-shift when viewed from Earth and how fast it is receding.

Due largely to its low galactic latitude (less than 8 degrees from the plane of the Milky Way) and direction along our line of sight toward the center of the Milky Way, which puts it almost directly on the opposite side of the gas and dust clouds near our galaxy's core, we can't see this object (or collection of objects and dark matter) directly, other than to note galaxy clusters (like Abell 3627) which seem to be a part of it or very near it. It is presumed to be the equivalent of about 150 to 250 million light-years distant, so its mass would need to be at least 10^16th solar masses and likely as much as half an order of magnitude greater.

Abell 3627's low redshift (z=0.016), direction, and distance lead us to believe it is low in the Great Attractor's gravity well, perhaps very near its center.

The current accepted constant is about 70 km/sec/Mparsec. This  of course does not apply to any local objects. Just how distant does an object have to be from us to start showing recession IAW HubLaw and constant. All my references say "significantly distant". 

I believe the current assumption is that recessional velocity swamps peculiar velocity at any z greater than 0.2 ... but I'd have to go look that up  to be sure. At any rate, you must go out several hundred million light-years to start to see cosmologically significant shifts.

When you say that the Hubble flow "does not apply to local objects" you're not going quite far enough, so I infer (and could be wrong) that you don't understand the difference: it does apply to local objects, we don't notice it when we're nearby. If we were a cosmological distance away, and measured the Milky Way's recessional velocity, it would certainly show up!

Jeff I believe you mentioned the current radius of the visible universe is about 13 billion light years?

Not quite. I said that's roughly the distance to the observable horizon. The radius of the universe could be several times that value.

Please take the time to calculate how fast 2 objects 26 billion light years away from each other would be receding.

Each would appear to the other to have a redshift over 12 (which is as high as I can calculate reliably).

This I believe is why some think that space (which is low mass) is expanding. If objects travel through space and not along with it, then Hubble's Constant only applies as long as the universe is small.

Again, that's not exactly correct. It's a conclusion you are making based on a flawed assumption. The Hubble Constant's precise value is a hotly debated topic among researchers. You would be safe to assume it lies in the range of 70 to 80, but some researchers have it as high as 100. Many different sets of data, made using different technologies and methodologies, seem to agree it is well above 50. Red-shift/distance calculators rely on other parameters, too, and the answer you get for "absolute" distance will depend on their values.

Of course the big band aide is always available when amendments are needed: Inflationary epoch. 

Call it a band-aid if you will, but it fits the data. There is nothing wrong with amending a theory to fit the data. That is part of how science works. Inflation is one of several amendments, made over half a century, to the BBT. I should point out that inflation has more than redshift observations to support it. Current ideas about the unification of the four fundamental forces fit quite neatly into a framework which allows symmetry-breaking and separation of gravity from the other forces to cause the requisite expansion.

We know the Earth moves through space as observed locally. Is the theory of space expansion solid?

Again, it fits the observations. So does the idea (not an established theory, nor even a credible hypotheses) of "old light" (some call it "tired light"). No mechanism to explain tired light has passed its tests.

Could it be that distant objects simply move through space?

Absent expansion and inflation, some of them (the ones with giant redshifts) would have to move at appreciable fractions of the speed of light.

Is there another explanation for red-shift?

None that have passed the requisite tests -- at least none that have won over the BBT proponents.

I believe this is part of another thread.

By all means ... first, however, do take the time to read Voyage to the Great Attractor, or Simon Singh's Big Bang ...

 Kool Data Jeff.

No reason not to believe something lies beyond our visible boundary but if the horizon is about 13 billion light years and the diameter is about 26 billion light years then you say the redshift would be about 12 for objects at opposite ends. What relative velocity would that correlate to? 26 billion divide by 3 million = 8666. Multiply that times the constant and you get 606,666 km per sec. This would mean that at that diameter either space or the objects would be moving about light speed away from each other. Any objects or space beyond that diameter would exceed light speed.

Can space expansion exceed light speed? I don't know. Not sure how the near void of space could be expanding anyway. At least not with sufficient umph to push galaxies along with it. It would seem to be like trying to blow over a mountain with only your breath.

When I talk about the epoch as a band aide I just mean it cannot be identified as a firm amount. Currently, based on our horizon, the value for the epoch is an early expansion of about 10xE50. Put in place to explain the bigger than thought universe that appears to be in contact beyond the distance allowed for distant parts of the universe to "know" about each other.

As the universe gets bigger they will simply update the amount of inflation. They will also have to periodically have to adjust the age of the universe too and this of course will have to adjust the temperature of the CMB which right now if believe to have cooled to the exact temperature it should be at based on a 14 billion year old universe.

I have trouble accepting a constant that is currently under debate with a range or error over 30km/sec. The constant value for the speed of light has no such error. My point is that if we can show that it is not a constant but only a variable, then we should lower its position on the "truth" scale a bit. 

BQ 

brooksquest:

 ...

No reason not to believe something lies beyond our visible boundary but if the horizon is about 13 billion light years and the diameter is about 26 billion light years ...

The diameter would be considerably larger. Cosmologists explain this as being due to the curvature of space.

... then you say the redshift would be about 12 for objects at opposite ends. What relative velocity would that correlate to? 26 billion divide by 3 million = 8666. Multiply that times the constant and you get 606,666 km per sec. This would mean that at that diameter either space or the objects would be moving about light speed away from each other. Any objects or space beyond that diameter would exceed light speed.

Ignoring that it is the fabric of space-time itself that is stretching, that is the effect we'd observe ... and do, in fact, observe. When z is very large, the apparent velocity is light-speed-ish.

Can space expansion exceed light speed? I don't know. Not sure how the near void of space could be expanding anyway. At least not with sufficient umph to push galaxies along with it. It would seem to be like trying to blow over a mountain with only your breath.

It gives the appearance of exceeding light speed. A very good explanation of this is given by Sten Odenwald in Patterns in the Void.

When I talk about the epoch as a band aide I just mean it cannot be identified as a firm amount. Currently, based on our horizon, the value for the epoch is an early expansion of about 10xE50. Put in place to explain the bigger than thought universe that appears to be in contact beyond the distance allowed for distant parts of the universe to "know" about each other.

Yes, that was the early justification for inflation: without it there was no way to explain the uniformity of the CMB. The BBT predicts that everything we now observe was very much nearer at early epochs. It did not predict it nearly enough. Inflation addresses that problem by rapidly accelerating the expansion. While no mechanism for the acceleration was proposed initially, the inflation theory is now presumed to be caused by a separation of the four fundamental forces -- where gravity initially split from the other three rather dramatically.

As the universe gets bigger they will simply update the amount of inflation. They will also have to periodically have to adjust the age of the universe too and this of course will have to adjust the temperature of the CMB which right now if believe to have cooled to the exact temperature it should be at based on a 14 billion year old universe.

I have trouble accepting a constant that is currently under debate with a range or error over 30km/sec. The constant value for the speed of light has no such error. My point is that if we can show that it is not a constant but only a variable, then we should lower its position on the "truth" scale a bit. 

I take your point, but this is how science works. It's why we use phrases such as "currently-accepted value" ... When there is no agreement on a measurement (and remember, Ho is pretty much the grandaddy of all measurements!), its value will change as new data, technologies, and methodologies are applied to it. That's the nature of science.

Otherwise we'd still think geocentrism works.

The conclusion many years ago that red-shift was due to recession remains the foundation for The Big Bang Theory. This is the key as mentioned in other threads that unlocks the door to what is really going on "out there".

The theory states that at its origin, the universe was very dense ( a point ). I find it amazing that all the matter that would become the universe could come together at a point prior to the Bang itself and yet we restrict ourselves in talking about "before" the Bang. All we can see happened after an event that does not explain itself.

How does empty space expand? What does it expand into? Emptier space?  

The universe is flat with critical density so there is no proof of curved space. 

There is no reason to believe that anyone, anywhere in the universe would be near the edge of it all.

BQ 

brooksquest:

The universe is flat with critical density so there is no proof of curved space. 

There is ample observational evidence that gravity curves spacetime. While that is not the same curvature I mentioned, it is curvature nonetheless. The curvature I mentioned is calculated based on assumptions, rather than observations.

There is no reason to believe that anyone, anywhere in the universe would be near the edge of it all.

Logic works equally well either way. So there is no scientific reason to believe there is not. Absence of evidence is not evidence of absence.

If you assume the universe is not infinite, then it has at least one edge, and perhaps many edges. Such an edge might lie within an intelligent being's observable horizon, as long as you make at least these two assumptions: (a) there is intelligent life in the universe, besides our own; (b) intelligent life besides our own can arise elsewhere in the universe within a timespan of a few billion years (short enough to lie with an observable horizon limit of the "beginning").

According to the BBT, the universe we observe today was created by the BB itself. It therefore began with the t=0 BB event. It therefore is finite. It may be unbounded as far as we can tell, but if it had a beginning then it is finite by definition.

From the standpoint of pure logic, it is no more difficult to provide a universe with a beginning than it is to provide a universe without one. It is simply a matter of each interpretation having different initial conditions. While it is tempting to state that since we can't "see" all the way back to "the beginning" then the universe must be infinite, it is no more (or less) logical than saying that it is finite.

brooksquest:

How does empty space expand? What does it expand into? Emptier space?  

I think you would enjoy Patterns in the Void.

So far as we know, there is no perfect emptiness. The fabric of spacetime permeates space. Gravity and spacetime may very well be equivalent.

Why would we think spacetime itself couldn't expand?

 It is a good question. 2 possibilities. Space does expand or it doesn't. We cannot prove that it does so if it doesn't then how do we account for superluminal motion at great distances. The current model is based on the assumption that space can expand. Is space different between distant galaxies than it is locally? Why would we assume that it is? If the expansion is accelerating then how can galaxies cluster and supercluster now? Space expansion would tend to not allow new galaxies to form and would suggest that at great distances galaxies would now be isolated far from other galaxies at their actual, not observed, locations. If space expansion means that our "close to nothing space" is becoming less something would it eventually lose its ability to support matter? Gravity does play a key role on the largest scales universally as the most abundant force in the universe. Again I ask, what is space expanding into? We find ourselves once again selfishly assuming a boundary between the universe and the outside unknown. I have already shown that this boundary is not real.

BQ 

brooksquest:

 It is a good question. 2 possibilities. Space does expand or it doesn't.

Once more into the breach ...

We cannot prove that it does ...

Apparently you aren't willing to accept the work of many astronomers/astrophysicists over the past half century. You talk often about scrapping what we've been told and exercising our imaginations to come up with new ideas. Well, BBT, inflation, expansion -- those were new ideas once, and have stood the test of time since. There are several lines of evidence leading to the conclusion that space is expanding. It's okay if you want to ignore those. But put something observational in place of them ... the musings of an imaginative mind don't adequately close the gap ...

... so if it doesn't then how do we account for superluminal motion at great distances.

I'll bite ... how?

The current model is based on the assumption that space can expand. Is space different between distant galaxies than it is locally?

Certainly it's different:

1. It's larger (there's very much more of it).
2. It's more tenuous (there's less in it).
3. It's very much farther away (we're immersed in locality).
4. There's less gravity there (a consequence of #3).

 Why would we assume that it is?

Another interesting reference covering all the points of this discussion (and more) is Joseph Silk's On the Shores of the Unknown.

I have a question.  Much has been made in this thread, and others, of the reliability of the red shift as a means of determining distance and , by extension, age.  The point has been made that it would seem logical for light, during it's travel from the most distant objects that we see, to interact with dust, gas, dark matter, etc. and thereby have it's wavelength effected (an artificial red shift).  What is the real likelyhood of that interaction?  We know that galaxies, when they collide, suffer no actual, physical contact, there are no massive smash-ups of stars and planets because a galaxy is more 'empty space' (space in the context of the interval between objects, not space-time) than it is actual matter.  If that is the case then I would expect the inter-galactic void to be even more empty.  There would seem to be very little for light to interact with.  When it does, as with gravitational lensing, we accout for that.  I know this is rather simplistic thinking, but that's just the kinda' guy I am.

Thanks in advance for any input.

zachsdad:

I have a question.  Much has been made in this thread, and others, of the reliability of the red shift as a means of determining distance and , by extension, age.  The point has been made that it would seem logical for light, during it's travel from the most distant objects that we see, to interact with dust, gas, dark matter, etc. and thereby have it's wavelength effected (an artificial red shift).  What is the real likelyhood of that interaction? 

That's the idea of tired light. On the face of it, the idea seems reasonable. However, there is no known mechanism by which such interactions could shift the light's frequency without also affecting its momentum. So it doesn't fit the evidence.

Another factor that tired light can't explain is the time dilation of supernovae. We observe that more distant supernovae of a known type (and therefore light curve over time) seem to have their light curve stretched. The more distant the supernova, the more its curve is stretched. If redshift were due to tired light instead of distance, then the light curve's duration would be independent of distance. The  2001 Goldhaber Supernova Cosmology Project study of such supernovae produced data like this:

where the red line shows what would be predicted by tired light and the blue line shows what would be predicted by distance-based redshift. The black line represents a least-squares "best fit" to the data. Since the blue line and black line very nearly coincide, we conclude the distance-based explanation is correct and tired light fails.

Similarly, tired light fails to predict the temperature of the CMB (but cosmological redshift nails it) . Also, studies of the surface brightness of distant galaxies show that redshift fits the curve extremely well whereas tired light would not fit it at all (like the supernova example).

We know that galaxies, when they collide, suffer no actual, physical contact, there are no massive smash-ups of stars and planets because a galaxy is more 'empty space' (space in the context of the interval between objects, not space-time) than it is actual matter.  If that is the case then I would expect the inter-galactic void to be even more empty.  There would seem to be very little for light to interact with.  When it does, as with gravitational lensing, we accout for that.  I know this is rather simplistic thinking, but that's just the kinda' guy I am.

When light encounters a medium (a dust cloud, glass, hydrogen gas, etc.) it is absorbed and re-emitted (either as heat or as light with a shift in wavelength and momentum). In effect, it is either blocked by the medium or it takes on the spectral characteristics of the medium. In the simplest case, a photon which encounters a cloud of hydrogen gas may strike a hydrogen atom. Its energy is absorbed by the atom and raises the atom's potential by the same amount. The unstable electron thus energized emits another photon, of exactly the same energy and frequency, to restabilize the atom. When we detect this second photon, its energy and frequency are indistinguishable from the original except that it has picked up the spectral signature of the atom. Its momentum remains the same. This is explained by the theory of quantum electrodynamics.

The other case is that the incoming photon is blocked ... it loses momentum (energy) and that loss is detectable either as a larger frequency shift (say, to that of the infrared where it would be detected as heat) or as a measureable loss of momentum. In the aggregate light from a distant source, we don't see this loss of momentum (which loss would be predicted by tired light), so the tired light scenario doesn't match observation.

Additional interesting reading is Ned Wright's Cosmology Tutorial (click here).

 One of the biggest problems with the BBT is that the theory does not explain itself. It doesn't explain how it occurred. We only have observations of what happened after. Some observations have been interpreted pretty well. Others have practically invented ghosts and goblins to explain what is being seen. Critical density was so short in explaining a flat universe that "dark energy" was made up from the imagination as having to exist to account for it. No one has ever detected dark energy! Oh, but it must be there because we see it's effect. Eintein's blunder cosmic constant was pulled out of the closet and reinserted into the equation under the alias of dark energy. Because it gave Albert a post mortem pat of the back it was easier to accept as a credible explanation. Without it and the epoch, the BBT falls completely apart based on observations. Band aides are for boo boos.

I showed you that we should not assume an "edge" to the universe because we can see far beyond anyone's edge who is it at what we think is our edge. You do understand that he should be able to see far beyond ours. Each edge infinitely extended by another observer.

When I look at HST deep sky images, the galaxies appear crowed out to the smallest dots in the image. So you believe we are closer to the center where the BB took place huh? Interesting.

BQ 

brooksquest:

 One of the biggest problems with the BBT is that the theory does not explain itself.

Neither, for example, does mathematics. It is invented, as it were, from whole cloth. That doesn't invalidate either.

What would invalidate either is to demonstrate they don't work (don't match observation). When a theory doesn't match observation, it is scrapped or modified. That's the way it works.

It doesn't explain how it occurred. We only have observations of what happened after.

Which is a direct prediction of the theory. That, alone, doesn't validate the theory, but it can't invalidate it, either.

Some observations have been interpreted pretty well. Others have practically invented ghosts and goblins to explain what is being seen. Critical density was so short in explaining a flat universe that "dark energy" was made up from the imagination as having to exist to account for it.

Again, you oversimplify. Use of terms like "ghosts" and "goblins" deprecates the work of many reputable scientists who developed what we call today the standard model. Not a nice way to argue a point ... nice: a word which here is meant to be taken in its mathematical sense.

No one has ever detected dark energy!

Not precisely correct ... I certainly would accept, however, that its existence (while generally accepted by standard model cosmologists) is still debated.

Oh, but it must be there because we see it's effect.

Pardon me, but "Duh." In another post you make this same point non-pejoratively about gravity (I think what you said there was that it a mechanism for how it works has not been proved).

Eintein's blunder cosmic constant was pulled out of the closet and reinserted into the equation under the alias of dark energy. Because it gave Albert a post mortem pat of the back it was easier to accept as a credible explanation. Without it and the epoch, the BBT falls completely apart based on observations. Band aides are for boo boos.

Without arguing the point, I'll just point out that you are again perhaps dramatizing here with "falls completely apart" and "boo boos" ... we do certainly differ on those points!

I showed you ...

No, you asserted ...

that we should not assume an "edge" to the universe because we can see far beyond anyone's edge who is it at what we think is our edge.

What you did was postulate a thought experiment without observational data to back it up. In fact, you developed a thought experiment which can't be observed (according to the theory). If one can't observe it, one can't prove it by not observing it. I'm not arguing with you, personally, but with the method you're using to assert your point. As long as we are allowed to take it as assertion, then fine.

You do understand that he should be able to see far beyond ours.

I do not, and should not (logically). Consider the case where each of us has different technology and methods. We should each have our own observable horizon, but they should differ.

Each edge infinitely extended by another observer.

That is not my assumption, nor would I agree with it, if you're talking about the earlier thought experiment with two observers, one of whom is "nearer the edge" than the other. I am certainly not assuming an infinite universe. One can postulate it as a straw-man to talk about an hypothesis, of course.

When I look at HST deep sky images, the galaxies appear crowed out to the smallest dots in the image.

Of course they do. The HDF and HUDF images, for example, are very, very tiny portions of the sky. One of them includes only a mere handful of foreground (Milky Way) galaxy stars. No intergalactic stars at those distances would be visible. How could you expect to see anything other than those galaxy images or the cosmic equivalent of George Carlin's Hippy-Dippy Weatherman's "Forecast for this evening: Sunset, followed by widely scattered dark!"? The spaces between the galaxies represented by the pixels in those images are vast.

So you believe we are closer to the center where the BB took place huh? Interesting.

I do not, nor have I stated that. You are free to infer anything you like. Perhaps I missed something ... I'll go back and look ...

OK, I looked all the way back to the beginning (this is quite a thread!).

I've said the following about a center:

• According to BBT we can't locate a center.
• It is okay, for the purposes of argument, to postulate that any object which has an extent also has a center, or centroid (and there is a difference).
• In one of your thought-experiment examples we went back and forth about two observers and their separate observable horizons. I postulated, for the sake of that discussion, that one observer was nearer an edge.
• In various posts and replies we have talked about the center and possible edges.

I have not stated, anywhere I can find, that:

1. The universe has a center.
2. We are near the center.
3. I believe there is a center.

Just to be resoundingly clear on this point:

• I do not know whether there is a center.
• I do not believe the universe to be infinite, in fact I adamantly disbelieve it (because I believe it had a beginning). I scientifically believe that it had a beginning, a very specific one: offering the BBT standard model and supporting observations.
• I believe (scientifically and mathematically) that it can have a center, at least for purposes of discussion using classical mechanics, and I believe it because it has an extent (at least an observable extent). For me this is a matter solely of practicality: the universe is so large, and we have observationally explored so little of it, and so tentatively, that even if it had a center with a big cosmically-observable blinking sign that said "here I am" there is no practical reason to suspect we have noticed it, or will anytime soon.

Hello All

Its funny that the Big Bang Theory is theoretical and not based on actual observations and geometry.

Somehow its been taken to be a fact and from there it has been accepted by Schools, churches and politics as the working model.

Harry Costas:

Hello All

 

Its funny that the Big Bang Theory is theoretical and not based on actual observations and geometry.

It's not theoretical, it's theory. There's a vital difference.

An established theory has proposed arguments that can be tested, have been tested, have passed those tests, and thus has been adopted by working scientists as a model for moving forward.

The BBT is all of these.

The preponderance of observational evidence is explained very well by the BBT.

Somehow its been taken to be a fact and from there it has been accepted by Schools, churches and politics as the working model.

That somehow is called the scientific method. The BBT is not metaphysics. It's science.

 Jeff,

When we talk about someone at the edge looking toward us let's just assume equal technology. For the sake of this discussion it would not matter one way or the other because the fact remains that the diameter of what he thinks the universe is, is doubled by our knowledge of what lies beyond his view. IF YOU DO NOT BELIEVE his observations would double our universal diameter then the only explanation would be that we are closer to the center of the BB universe than he, or anyone else at the edge is. So your disbelief in sequencial doubling leads to us being near the center of it all. We may as well call for another inquisition.

The BBT states that at its origin, the universe was very dense. How did it get dense? Oh, we can't talk about it. Gravity would have to be involved in producing density. Oh, but we can't talk about it. It would have taken allot of time for it to become dense before it "exploded". Oh, but we don't think it exploded like a bomb, but we still reverse Hubble's Law and constant to see how old it is. Not being able to talk about how the event itself happened is like censorship. If a tree fell in the forest and no one was there, did it make a sound? Can we talk about that?

2 + 2 = 4

Philosophy tells us this is "true". Nothing "yet" has told us that the big bang is "true". Math is beautiful and is far beyond the level of importance of what we think caused the universe to be born. Please do not belittle mathematics.

BQ
 

Hello All

If the Big Bang has been tested than show me the tests without ad hoc ideas supporting the theory.

Than apply science to the theory.

I can give you hundres and thousands of links supporting the Big Bang, but! any infinite number times zero equals zero.
=============================================

Shapeshifting towards a
New Cosmology

http://www.ceptualinstitute.com/uiu_.../cosmology.htm


Theoretical cosmology

http://cosmology.uct.ac.za/research/..._cosmology.htm

Our universe in reality has parts that are expanding and parts that are contracting.

In addition we find extremely large voids billions of year across that the big bang cannot explain.

brooksquest:

 ... the fact remains that the diameter of what he thinks the universe is, is doubled by our knowledge of what lies beyond his view.

I guess I'm just dense. I do not get the point above. If you consider our observable horizons being the same (because we have the same technology), and we are each at the center of our respective observable horizons -- imagine we are each in a spherical shell of technological visibility, from our own perspectives -- then what are the cases where overlapping these spheres leads to one person's view doubling the diameter of the other's? The only such case I can imagine is when the spheres intersect at a point and the two observers are looking (in opposite directions) along the radius of their own sphere and through the center of the other observer's sphere. From the perspective of each observer, the line of view through the other observer would double the overall diameter ... but only that view would do it. That still doesn't tell you anything at all about the overall size, or shape, of the universe at large. What am I missing?

So your disbelief in sequencial doubling leads to us being near the center of it all. ...

The BBT states that at its origin, the universe was very dense. How did it get dense? Oh, we can't talk about it.

I did not say, nor does BBT theory posit, that we can't talk about it.

I said, and BBT theory supports, that we can't know it, we can't observe it.

So, any talk about it must be classed as mathematical speculation (for which there may be good justification, but in the absence of observation what do you have?) or metaphysics. Neither is science, per se, though both are of concern to many scientists.

Gravity would have to be involved in producing density. Oh, but we can't talk about it.

We certainly can talk about it, and BBT -- especially inflation and the CMB research -- talks about it at great length. But only post-BB. According to BBT, for a period of several hundred thousand years immediately after t=0 (again, the BB's initial instant, not necessarily that for the universe as a whole, although that is the way I read the BBT) the universe was so hot that atoms couldn't form and photons could decouple. It was like a fog through which we can't see ... that is, there is a lookback time beyond which we'd encounter this fog and observational evidence would not be forthcoming.

It would have taken allot of time for it to become dense before it "exploded".

Not if spacetime were created by the BB. The BBT itself can only be mum on what occurred prior to the BB's initial instant. It can't prove, since there can be no observations prior to that time -- again, assuming the premises of the BBT -- or disprove it. BBT supporters simply can't know about earlier times. Some BBT supporters would agree that space and time themselves did not exist prior to that instant. Some BBT supporters would agree that space and time are one and the same and did not exist prior to that instant. And some BBT supporters would agree that gravity is, in fact, the fabric of spacetime and did not exist prior to that instant. But other BBT supporters would disagree with these points. None of which invalidates the premises observationally.

Oh, but we don't think it exploded like a bomb, but we still reverse Hubble's Law and constant to see how old it is. Not being able to talk about how the event itself happened is like censorship. If a tree fell in the forest and no one was there, did it make a sound? Can we talk about that?

Yes, and in the same way our understanding of physics tell us that a sound occurred when the tree fell. Acoustic waves would be created. If they fell on deaf ears, or no ears, they would still exist. But with the BBT, there is that foggy era beyond (further back in time) photon decoupling. It was a very foggy time. We can run our simulations (based on all kinds of initial conditions one cares to conjure) backward in time as far as we care to speculate. But when it comes to being able to demonstrate the theory works, there are only two choices:

1. We admit we can't have observational evidence further back than the era of photon decoupling, and we admit anything earlier is conjecture (admittedly it might have a sound hypothetical basis).
2. We select our parameters and initial conditions such that the computer model results in a universe that is not at odds with that which we see today. (Otherwise, the conditions and/or model fails, or we must postulate that the universe we see around us today is only one of many possible results -- which again takes us into the realm of metaphysics.)

2 + 2 = 4

Philosophy tells us this is "true". Nothing "yet" has told us that the big bang is "true". Math is beautiful and is far beyond the level of importance of what we think caused the universe to be born. Please do not belittle mathematics.