Astrophysics/Location in the Universe
QUESTION: Hello. I kind of have 2 questions.
When reading about the shape of the universe, well, frankly I donīt understand at all, but I donīt worry about that too much. What I do wonder about is:
Why, if the universe came from a point that is expanding outward, and we have maps of the distribution of the matter in the universe, why canīt we determine where we are within the universe? Why canīt we locate ourselves relative to the point where the singularity happened, from the point from where presumably everything is is flying away from?
I donīt know if I should ask my second question in another email, or wait and ask in a few weeks, so tell me how I ought to do it please. In the mean time, my other question is this:
Regarding the electromagnetic spectrum, are there limits to the frequencies? At what frequencies do gamma rays and radio waves end, on the higher and lower ends, respectively? Is it infinite? Could you break it down for me?
Thanks for your time. I was excited when i came across this site. It seems great. I love talking to experts about anything, but I love astrophysics a lot.
The existence of (partial) 'maps' showing the distribution of matter (e.g. galactic clusters etc.) in the universe is not a basis for the determination of our position relative to the origin "point" (which is really a loosely used term) of the cosmic inception. Remember that the inception - or what we call the "Big Bang" (actually more the initial unfolding) was an expansion of both space and time, hence all future positions become conflated in terms of localizing any other (space-time) position relative to it.
One way, or rather crude analogy used, to explain it in prosaic terms, is to compare to an expanding balloon with its surface full of ink dots. As the balloon expands then there is no ink dot from which a unique position can be ascertained relative to the center of inflation-expansion. We are in a similar fix, since we are in a galaxy cluster (Local Group) which is also part of the self-same expansion as all other galactic clusters, and none offer a supreme position in terms of special reference frames.
Yes indeed, "everything is flying away" from us, but it's flying away from all other observers in all other galaxy clusters too! So, who's right and who is the special observer from which the start point can be reckoned? Well, there are none!
In terms of electromagnetic waves, there are generally defined "limits" that most physicists, astronomers adhere to in assigning wavelengths, such as gamma rays etc. In the case of radio waves we are generally looking at anything from 10 cm onwards - beyond. For gamma waves we're generally looking at all radiation with wavelength of 0.1 A (angstrom) or less. If 1 A = 10^-8 cm, then we're talking of wavelengths less than 10^-9 cm, or 10^-11 m. Again, bear in mind these are accepted conventions.
I am not sure what exactly you mean when asking, "is it infinite?' - I presume that you mean the wavelength limits. As regards infinite anything that's more a concept peculiar to mathematics than physics, so I would not use the term 'infinite' - but rather 'indefinite'. In other words, the wavelength of radio waves can go on indefinitely higher (e.g. beyond 10 cm) just as the wavelength of gamma waves can go on indefinitely lower (e.g. less than 0.1 A).
Ultimately, one day, observational optics-physics may determine what -if any- the end points of the wavelengths are. I.e. can a radio wave be so large (say 1 Ly across) that its Stokes' parameters can't even be assessed, or its basic properties? Maybe. We don't know but we do know in order to be detected at all radio waves must fall within certain physical limits, i.e. brightness temperature, received flux, solid angle etc. One also needs to look at properties of the antenna -receiver such as beam width, gain, antenna temperature, etc. So we need to be very wary about using terms like "infinite" in terms of observing parameters.
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QUESTION: Thanks (Dr.?) Stahl.
Regarding the first question, I guess I just canīt conceptualize it very well. But let me ask you this- we know that some objects are moving away from us faster than others, is this just do to local gravitational effects or is there a larger pattern behind it? Can we see any larger patterns of the expansión on the universe? Or am I just still totally missing it?
Also, just randomly asking- what would happen if the frequency of radio waves went so low that it, metaphorically speaking, ended up looking like a flat line?
ANSWER: Hello again,
Some objects are moving away from us faster than others, because being at greater distances they have increased velocity (of recession). You may want to Google "The Hubble Law" in relation to this where you will find that the velocity v is related to the distance, d, and the Hubble constant H, by: v = Hd
so the greater the distance, d, the faster the recessional velocity.
In terms of "larger patterns" pertaining to expansion, the only one of which I am aware concerns the fact that it is accelerating owing to the presence of dark energy. You can read more on dark energy in this earlier answer (googling it is also a good idea):
I also suggest reading Chapter 5 of Lawrence Krausse 'A Universe from Nothing'. In this chapter ('The Runaway Universe') Krausse explains the difficulties in ascertaining acceleration of the cosmos, and also argues that one group's results may have been prematurely adopted.
Re: the frequency of radio waves being "so low" they are metaphorically a "flat line", no. The frequency is related to the wavelength, L, by:
f = v/ L
Thus, lowest frequency would correspond to greatest wavelength. But as I noted in part 1, given the limitations of our receivers, antennas, as well as the variable parameters of radio sources (flux, etc.) we simply cannot be sure what that (observational) limit is, including what conceivable phenomenon might generate it. Maybe L is 100m, or maybe even 1 Ly (though this seems to be doubtful). But in any case, it's difficult to imagine a "flat line". The reason is that with a properly designed "radio telescope" - of proper dimensions, properties- the wave ought to still be detectable, so it wouldn't be a "flat line"!
Also, just because humans can't construct an effective design to capture such extreme waves doesn't mean another civilization- much more advanced- is foreclosed from doing so!
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QUESTION: Other advanced civilizations is more of a religious question, isnīt it? I mean, itīs not really a human matter.
And maybe I get it a bit. The farther away it happened the farther and farther away it continues to happen. Lensing and so forth.
I think that the local super cluster is moving in a common direction relative to the rest of things.
I believe I have found the answer to my question: Of the universe mass map things I have seen- and correct me if Iīm wrong- to localize ourselves, we just must look to the middle of it, those maps are made with us at the center...?
-No one cares about the end of the Universe, unless itīs made of bubbles.
Stephen Baxter in Vacuum Diagrams
Actually, the possible existence of other advanced civilizations is by now means a religious question. We actually have a SETI program ('Search for Extra-terrestrial Intelligence')that has contributions from astrophysicists, other scientists (exo-biologists) and is based on a radio spectrum search for possible signals based on probabilities computed from existing science (i.e. type of star, whether it has a spectral class similar to the Sun, and hence plausibly a 'habitable zone' for possible planets like the Sun).
Further spurring this is the search for exo-planets (again, you can google this term) and we've found over 500 already. If these planets exterior to our solar system exist then it's a good bet that some form of life-supporting planet is also out there and that life may well be intelligent and even advanced.
Also, assuredly, if another civilization is detected it will be a major human matter! Think of the impact on politics, religions, even our existing science. So, given this, the search for such intelligence is certainly a "human matter", as indeed all worthwhile scientific inquiry is.
Alas, I am still not sure you "get it" from your brief take on expansion. It has nothing to do with gravitational lensing - which does affect some galaxies but is not the basis for the Hubble expansion. I think what you really need to do is to google "the Hubble law" and carefully read through it. An even better strategy is to try to get hold of a basic astronomy text at a library and read through the sections to do with the Hubble law and cosmic expansion. What occurs to me in going through your questions is the need to do much more extensive reading. You can't hope to grasp these facets by only asking questions out of curiosity. You also need to fortify that curiosity with **actual books** (many may also be already available free on the net). The right books also will contain questions at the end which will test how much you have really understood. Is it something like school? Yes! But that's a good thing!
Some sites which feature free astronomy notes and books, as downloads:
I can certainly provide the guidance here at allexperts, but in the end I can't complete the mission of guaranteeing your firm understanding. That must be up to you. The more effort you put into additional reading, etc. the greater will be the payoff.
Part of this auxiliary reading must be to ensure you grasp that the expansion is differential in the sense that the greater the distance the greater the recessional velocity. We use red shift measurements of galactic clusters to determine this, meaning we observe the displacement of the spectral lines from their normal position then compute the velocity from this.
Basically, the key and critical idea to grasp is that the cosmos is expanding and the rates differ depending on how distant the object is that's observed in relation to the observer.
Re: your query on cosmic maps, see e.g. those related to the Sloan digital sky survey:
it is best not to take these too literally. For one thing, the survey is ongoing so hardly complete. For another, it only assays limited regions of the cosmos so can hardly be said to be an entire map of the cosmos. If not an entire map, it can in no way disclose our own position in relation to the whole. Moreover, again, by virtue of the expansion bear in mind you are not in any inertial reference frame such that you can absolutely say or claim you are "at the center" of it all.
Consider this example: you obtain a Google (satellite) map of one particular geographical formation, or place, say Madagascar. Having obtained that can you claim you are at the "center of the global map"? Hardly! In a way this limited domain obtained from Google satellite views is analogous to the limited cosmic maps assembled by the Sloan.
The key thing that you need to disabuse yourself of is that humans or the Earth are "at the center" of anything. The fact is, we aren't and this is one thing that the expansion definitely shows.
We just have to learn to live with it :)