Scientist don't assume, they do NOT do such thing. Scientist follow the scientific method then come up with a conclusion, but they do no such thing as 'assume'.
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Scientific method is a body of techniques for investigating phenomena and acquiring new knowledge, as well as for correcting and integrating previous knowledge. It is based on gathering observable, empirical and measurable evidence subject to specific principles of reasoning,[1] the collection of data through observation and experimentation, and the formulation and testing of hypotheses.[2]
Although procedures vary from one field of inquiry to another, identifiable features distinguish scientific inquiry from other methodologies of knowledge. Scientific researchers propose hypotheses as explanations of phenomena, and design experimental studies that test these hypotheses for accuracy. These steps must be repeatable in order to predict dependably any future results. Theories that encompass wider domains of inquiry may bind many hypotheses together in a coherent structure. This in turn may assist in the formation of new hypotheses, as well as in placing groups of hypotheses into a broader context of understanding.
There is a popular misconception, sometimes even taught in science classes, that a scientific idea progresses from being a hypothesis, to being a theory, to being a law, based on how much evidence has been established. This is not the case. Although scientists in different fields may use the three terms somewhat differently (especially the term "hypothesis"), the terms represent different types of scientific understanding which are not subject to the alleged progression.
Among other facets shared by the various fields of inquiry is the conviction that the process must be objective to reduce a biased interpretation of the results. Another basic expectation is to document, archive and share all data and methodology so it is available for careful scrutiny by other scientists, thereby allowing other researchers the opportunity to verify results by attempting to reproduce them. This practice, called "full disclosure", also allows statistical measures of the reliability of these data to be established.
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[edit] Elements of scientific method
There are multiple ways of outlining the basic method shared by all of the fields of scientific inquiry. The following examples are typical classifications of the most important components of the method on which there is very wide agreement in the scientific community and among philosophers of science, each of which are subject only to marginal disagreements about a few very specific aspects.
The accepted definition of the scientific method involves most of the following basic facets:
Observation. A constant feature of scientific inquiry, observation includes both unconditioned observations (prior to any theory) as well as the observation of the experiment and its results.
Description. Information derived from experiments must be reliable, i.e., replicable (repeatable), as well as valid (relevant to the inquiry).
Prediction. Information must be valid for observations past, present, and future of given phenomena, i.e., purported "one shot" phenomena do not give rise to the capability to predict, nor to the ability to repeat an experiment.
Control. Actively and fairly sampling the range of possible occurrences, whenever possible and proper, as opposed to the passive acceptance of opportunistic data, is the best way to control or counterbalance the risk of empirical bias.
Identification of causes. Identification of the causes of a particular phenomenon to the best achievable extent. For cause-and-effect relationship to be established, the following must be established:
Time-order relationship. The hypothesized causes must precede the observed effects in time.
Covariation of events. The hypothesized causes must correlate with observed effects. However, correlations between events or variables are not necessarily indicative of causation.
Elimination of plausible alternatives. This is a gradual process that requires repeated experiments by multiple researchers who must be able to replicate results in order to corroborate them.: All hypotheses and theories are in principle subject to disproof. Thus, there is a point at which there might be a consensus about a particular hypothesis or theory, yet it must in principle remain tentative. As a body of knowledge grows and a particular hypothesis or theory repeatedly brings predictable results, confidence in the hypothesis or theory increases.
Another simplified model sometimes utilized to summarize scientific method is the "operational":
The essential elements of a scientific method are operations, observations, models, and a utility function for evaluating models.[citation needed]
operation - Some action done to the system being investigated
Observation - What happens when the operation is done to the system
Model - A fact, hypothesis, theory, or the phenomenon itself at a certain moment
Utility Function - A measure of the usefulness of the model to explain, predict, and control, and of the cost of use of it
One of the elements of any scientific utility function is the refutability of the model. Another is its simplicity, on the Principle of Parsimony also known as Occam's Razor.
The following is a more thorough description of the method. This set of methodological elements and organization of procedures will in general tend to be more characteristic of natural sciences and experimental psychology than of disciplines commonly categorized as social sciences. Among the latter, methods of verification and testing of hypotheses may involve less stringent mathematical and statistical interpretations of these elements within the respective disciplines. Nonetheless the cycle of hypothesis, verification and formulation of new hypotheses will tend to resemble the basic cycle described below.
The essential elements[3], [4], [5] of a scientific method[6] are iterations [7], recursions[8], interleavings, and orderings of the following:
Characterizations (Quantifications, observations[9] , and measurements)
Hypotheses[10] (theoretical, hypothetical explanations of observations and measurements)[11]
Predictions (reasoning including logical deduction[12] from hypothesis and theory)
Experiments[13] (tests of all of the above)
Source and more info on the scientific method Click.The link has even more info on the scientific method, people, please do not comment without knowing thank you. And to the one word posters. Example:
QUOTE(Blue_Sphere @ Aug 25 2007, 11:48 AM)
Spooky.
QUOTE(Krayt12 @ Aug 25 2007, 12:07 PM)
...whoa...
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Sounds Big
You all agreed with the rules when you became a member:
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2e. Garbage posting: Do not deliberately make posts of little worth or that contain nonsense. This is usually done either for the purpose of increasing post count or to disrupt the forum by doing so in an attempt to bait others in to responding.
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4b. One-word comments: Do not respond to threads or gallery pictures with derogatory one word responses such as "Fake!" or "Photoshop!". If you think something is fake then say why you think that, elaborate on your response.
The universe has a huge hole in it that dwarfs anything else of its kind. The discovery caught astronomers by surprise.The hole is nearly a billion light-years across. It is not a black hole, which is a small sphere of densely packed matter. Rather, this one is mostly devoid of stars, gas and other normal matter, and it's also strangely empty of the mysterious "dark matter" that permeates the cosmos. Other space voids have been found before, but nothing on this scale.Astronomers don't know why the hole is there."Not only has no one ever found a void this big, but we never even expected to find one this size," said researcher Lawrence Rudnick of the University of Minnesota.Rudnick's colleague Liliya R. Williams also had not anticipated this finding. "What we've found is not normal, based on either observational studies or on computer simulations of the large-scale evolution of the universe," said Williams, also of the University of Minnesota.The finding will be detailed in the Astrophysical Journal.The universe is populated with visible stars, gas and dust, but most of the matter in the universe is invisible. Scientists know something is there, because they can measure the gravitational effects of the so-called dark matter. 
View: Full Article | Source: Space.com
Good statement, Torchwood. I do have a suggestion. This, and other voids are filled with neutral anti-hydrogen. That is hydrogen made from an anti-electron (positron) and an anti-proton. Anti-matter has anti-gravity, you know. Oh yes. Well known in my family of 1. Explains lots of things, including the soap-bubble medium scale organization of the universe. Anti-hydrogen would be neutral, and thus invisible. Since anti-gravity objects try to stay as far away from any other particles as they can, these bubbles produce an outward pressure on the matter around them, both dark and light. Where the bubbles collide there are strings of clusters of galaxies. Neutral anti-hydrogen atoms are light, and they push away from passing cosmic rays, which keeps them neutral, cool, and invisible. Since they are evenly distributed throughout the bubble, there would be no lensing effect. So they stay hidden.