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The Best Science Writing Online 2012
Showcasing more than fifty of the most provocative, original, and significant online essays from 2011, The Best Science Writing Online 2012 will change the way...
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Questions answered in this episode:
"Let's say I'm an alien on a ship 65 million or more light-years away. Using a telescope, I look at Earth and I see dinosaurs living their daily lives. If my ship started travelling towards earth near the speed of light. Would I see the dinosaurs moving faster--fast-forwarded?"—sl270703
"If all movement is relative, how can there be a speed limit? In order to measure speed, you have to measure it against something. So...what is the speed limit measured against?"—lordv27
"If a black hole's event horizon gets bigger every time its density gets bigger, i.e., it "absorbs" mass, why hasn't the whole universe collapsed into an enormous black hole yet? Shouldn't this kind of expanding black hole be getting bigger exponentially? And will this be the end of our universe and possibly the birth of a new one (or where ours began—a big bang)?"—Shaido666
Submit your questions for the next round of Ask the Experts by clicking here and posting in the YouTube comments (Google account required). And while you're there be sure to subscribe to the Spacelab channel for weekly videos on space and astronomy.
The question with the most "likes" will be answered in the next video by a new guest expert. Previous episodes have featured astronomer Caleb Scharf, astrophysicist Neil deGrasse Tyson and Scientific American's own editor in chief, Mariette DiChristina.
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59 Comments
Add CommentSpeed of light follow up: If two spaceships are traveling at 75% the speed of light towards each other, wouldn't they appear to be exceeding the speed of light to one another? If they collided, wouldn't that collision net out to exceeding the speed of light?
Reply | Report Abuse | Link to this@Gogela Yes, the two ships close on each other at 1.5 times the speed of light. But this poses no problem because no physical influence is outrunning light.
Reply | Report Abuse | Link to thisANOTHER speed-of-light question. The center of the galaxy is about 26,000 lightyears distant from earth. If a space traveler from earth traveled to the center of the galaxy at the speed of light, not at some close fraction of the speed of light but AT the speed of light, would not the journey appear to this person as instantaneous? Time slows down as one approaches the speed of light but AT the speed of light, does it not stop? Thus it should seem to the traveler that the trip to the center of the galaxy was instantaneous while observers on earth watched a long, 26,000 year journey. Is this not correct?
Reply | Report Abuse | Link to thisThe two spaceships would not appear to approach each other at 1.5 times the speed of light. They will experience time slower and still be under the speed of light. Remember speed is not absolute and neither is time.
Reply | Report Abuse | Link to thisAnything with mass cannot go the speed of light. Time would not stop.
Reply | Report Abuse | Link to thisQ1 - "... Would I see the dinosaurs moving faster--fast-forwarded?"
Reply | Report Abuse | Link to thisSorry, George: the correct answer is no, you would not see dinosaurs moving faster - you'd actually have seen them very quickly disappear, of course!
It was a trick question, after all, even if unintentional...
Q1 - "... Would I see the dinosaurs moving faster--fast-forwarded?"
Reply | Report Abuse | Link to thisI would have thought the light from earth would be massively blue-shifted by the approach speed so you wouldn't be able to actually see anything - though maybe you could decode the shifted radiation to produce the fast visual image??
Speed of light is the limit because of the fact that anything that moves faster breaks the law of causation. Since the law of causation is the basis of thermodynamical understanding of time, the limit is also the constituent of time. Moreover, the light also constitues the basis of information, hence , there is no way of knowing objects moving faster than light.
Reply | Report Abuse | Link to thisre: Q1
Reply | Report Abuse | Link to thisjt, wrong.
The Dinosaurs do appear to move faster. Note that these are images of the dinosaurs and not the dinosaurs themselves.
The formula you're used to for adding velocity in newtonian physics would be:
Reply | Report Abuse | Link to thisw = u + v
where "w" is the total velocity, u is the velocity of one object and v is the velocity of the other.
When you add relativistic velocities, you have to incorporate a correction factor. The formula is:
w = (u + v)/(1 + u * v / c^2)
where w, u, and v are as above, and c is the speed of light.
For low velocities, u*v/c^2 is a very small number, so you don't really notice it unless you're looking very carefully. The fastest object created by man was apparently the Helios 2 solar probe at 70,220 m/s or 0.0002342 c. Try to crash two of those together, the correction factor would be (70,220 ^2)/(299,792,458^2) = 5.49* 10^-8.
Plugging in the numbers for the Helios probe, the expected observed speed of the two probes heading towards each other would be 140,439.9923 m/s as opposed to the non-relativistic expected value of 140,440.
For the theoretical objects travelling at 0.75c, you'd get:
(0.75c + 0.75c)/(1+ (0.75c*0.75c/1c^2)) = 1.5/(1+0.5625) = 0.96c
to lawman108
Reply | Report Abuse | Link to thisin reply to pkoneil
Half right. No massive object can go at the speed of light.
THe second comment is not quite right. This is one of the thought experiments Einstein did in first discovering his theory. Imagine what a light beam experiences (if it could).
http://www.pitt.edu/~jdnorton/Goodies/Chasing_the_light/index.html
If time is measured by oscillations of a light wave, then according to this experiment time does stop.
"If a black hole's event horizon gets bigger every time its density gets bigger, i.e., it "absorbs" mass, why hasn't the whole universe collapsed into an enormous black hole yet? Shouldn't this kind of expanding black hole be getting bigger exponentially? And will this be the end of our universe and possibly the birth of a new one (or where ours began—a big bang)?"—Shaido666
Reply | Report Abuse | Link to thisActually, the universe probably existed as an infinitely extended black hole at the onset of cosmic expansion during our universe's current cycle (since singularities can not exist). It is also probable that when the current expansion phase ends the universe will collapse and once again become an infinitely extended black hole briefly before expanding again. There must be a short range (subplanck length) repulsive force that limits space contraction. In normal black hole formation, the black hole is in a state of 'gravistatic equilibrium' in which there is a stable balance between the gravitational and short range antigravitational forces because the matter outside of the black hole provides enough force to prevent instability within the black hole. However, when the universe finally 'dies' at the end of the current cycle it collapses in its entirety (instead of piecemeal) and the pressure between the the gravitational force and the antigravitational force become so great that the universe must expand in order to relieve this instability. A thermodynamic gradient is produced.
"If a black hole's event horizon gets bigger every time its density gets bigger, i.e., it "absorbs" mass, why hasn't the whole universe collapsed into an enormous black hole yet? Shouldn't this kind of expanding black hole be getting bigger exponentially? And will this be the end of our universe and possibly the birth of a new one (or where ours began—a big bang)?"—Shaido666
Reply | Report Abuse | Link to thisActually, the universe probably existed as an infinitely extended black hole at the onset of cosmic expansion during our universe's current cycle (since singularities can not exist). It is also probable that when the current expansion phase ends the universe will collapse and once again become an infinitely extended black hole briefly before expanding again. There must be a short range (subplanck length) repulsive force that limits space contraction. In normal black hole formation, the black hole is in a state of 'gravistatic equilibrium' in which there is a stable balance between the gravitational and short range antigravitational forces because the matter outside of the black hole provides enough force to prevent instability within the black hole. However, when the universe finally 'dies' at the end of the current cycle it collapses in its entirety (instead of piecemeal) and the pressure between the the gravitational force and the antigravitational force become so great that the universe must expand in order to relieve this instability. A thermodynamic gradient is produced. antigravitationalforce.com
Re. Q1 - wrong! The dinosaurs would have been seen to quickly disappear from the Earth!
Reply | Report Abuse | Link to thisGeorge says in the video (paraphrased) that the dinosaurs would initially be seen 65 million years into the past, after 65 million years of travel, they'd be seen 130 million years into the future. Sound reasoning, except the dinosaurs went extinct 64 million years ago! I told you it was a trick question!
I agree, we only have the understanding of the Universe of the theories we have been thought & Understand. Just read science and or education subject over the decades and eventually you find most of it has failed and new finding are revealed through more research.
Reply | Report Abuse | Link to thisCurrently, the Proton is to believe smaller as thought before and no one knows Why.
Many other examples can be named in theories of Genetics triads and resulting effects.
Even now as Einstein's theories stands for over 100 years, because we really haven't breed still smarter individuals yet and intellectually we're in a Slump, just as the economy doesn't mean that his formulas and theories will hold up as we discover more or find the Flaws in the Models.
As it stands, most believe in more advanced intellectual species, who might be living in other or even in this Galaxy. If & when we've been visited by UFO's at some point in time, as the majority like to believe it is very unlikely that they have mastered that feat by NOT traveling above the Speed of Light in Space or Time. Since Star formation is the typical easiest observation in the Universe that we're able to Detect Understand & Explain in (we believe) all detail, it's no surprise to me that we hang on to the Limit of the speed of light that cannot be exceeded by any other Matter.
After all, It's the limit of our calculations & observations that we understand life and the Physical concepts explaining our surroundings and not the Universe.
Time does not slow down - it is just that the atomic clock's timing changes when their relativistc mass/energy changes. That is why the GPS lab has to keep adjusting their ground and orbiting clocks to keep them is sync because they are at different relativistic mass/energies.
Reply | Report Abuse | Link to thisfor more see- http://novan.com/energies.htm
Thanks Alan, are you related to Sir Fred?
Reply | Report Abuse | Link to thisYou might find a new research report interesting:
Reply | Report Abuse | Link to this"A Clock Directly Linking Time to a Particle's Mass,"
http://www.sciencemag.org/content/339/6119/554
However, the extension of periodic processes such as the relativistic decay of unstable particles indicates that, for those particles, the progression rate of time has effectively been slowed relative to particles at rest.
"... If no time dilation exists, then those muons should decay in the upper regions of the atmosphere, however, as a consequence of time dilation, they are present in considerable amount also at much lower heights."
http://en.wikipedia.org/wiki/Time_dilation_of_moving_particles
In other words things moving faster than the speed of light would be invisible?
Reply | Report Abuse | Link to this"Yes, the two ships close on each other at 1.5 times the speed of light. But this poses no problem because no physical influence is outrunning light."
Reply | Report Abuse | Link to thisA contradiction. If no physical influence is outrunning light, how can any ship or 3rd party observer measure 1.5x speed of light? Is this an imaginary hypothetical speed? In physics, speed is a scalar quantity measured as change in distance over change in time between two bodies.
Re.: Q1...
Reply | Report Abuse | Link to thisActually, the current estimate for the Cretaceous–Paleogene extinction event is approximately 66 million years ago, so if the alien looked through a telescope 65 million years ago it would not likely have seen many dinosaurs running around - certainly no big ones...
1) The dinosaurs will not appear to move faster nor slower because the speed of light is constant regardless of the motion of the observer.
Reply | Report Abuse | Link to this2) The speed limit is measured against any observer and it remains constant regardless of the observer's motion.
3) The galaxies are too far from the black holes to get sucked by gravitational force.
1) While dinosaurs wouldn't be around for long, the hypothetical spaceship approaching Earth at nearly the speed of light for about 65 million years would receive the light emitted from Earth over a period of 130 million years, travelling essentially at the speed of light in a vacuum.
Reply | Report Abuse | Link to thisThe relativistic observer's effective 'frame rate' would be much greater than the relatively static observer - the surviving raptors and/or birds would appear to be moving really fast. That'd be one helluva telescope that could resolve a bird at a distance of 65 million light years!
And the telescope would have to be looking in extreme blue-shifted wavelengths to compensate for the approach-speed doplar shift.
Reply | Report Abuse | Link to thisThe Schwarzschild radius is proportional to the mass with a proportionality constant involving the gravitational constant and the speed of light:
Reply | Report Abuse | Link to thisr(sub)S = {2Gm}/{c^2},
thus the Schwarzschild radius can be defined for any mass, e.g. electron, proton, earth, sun, galaxy, etc. If the relevant mass is contained within the S-radius, we have a black hole. If the universe is not still a black hole by this definition, then surely it must have been one when it was much smaller sometime in the past. That is, if one accepts the standard expanding universe picture from very compact beginnings. So, obviously the normal black hole picture with a density singularity at the centre cannot be the full story, and smaller and therefore denser black holes can cheerfully exist within a larger, less dense black hole. Elementary..?
While I accept that if one traces genealogy back far enough, we're all related somehow, I don't know my specific relationship with either of the "famous" Hoyle's: red (astronomer) or Edmund (card game rules).
Reply | Report Abuse | Link to this"Fred" not "red" sputid tyops.
Reply | Report Abuse | Link to this@alanhoyle When calculating closing speed, you do not apply the Lorentz formula, because you are not changing frames of reference. See, for example, http://snurl.com/26a744s
Reply | Report Abuse | Link to this@jtdwyer Yes, of course, I'm neglecting KT! But to be technical, we didn’t specify when the trip began; it might well have been during the epochs of the dinosaurs.
Reply | Report Abuse | Link to thisIf the Big Bang happened less than 14 billion years ago and the speed of light is as fast as anything can go how can the universe have 150 billion light year diameter?
Reply | Report Abuse | Link to thisHow does science account for the energy which gets released in an atomic explosion? Where did it come from and was it the same or greater in amount of the energy needed to form the atom in the first place?
Reply | Report Abuse | Link to thisgmmuser - yes, the problem statement did specify "65 million or more light-years away" and did not specify a departure time, although your explanation indicated that observations during the trip would reveal high speed dinosaurs... Of course, I'm just nitpicking - your answer what substantively correct!
Reply | Report Abuse | Link to thisYes the dinosaurs will appear to move fast if the ship was moving near c 65 million yrs ago. I presume the light rays left earth before the ship started traveling which is more logical since in the first case the ship would have been traveling for 65 million yrs. In the second case, you will not see the dinosaurs moving fast or slow because the light rays are moving at constant speed.
Reply | Report Abuse | Link to thisIn the two ships scenario, none of them would measure a speed greater than c. But each would see the other in slow motion (time dilation) since both ships are inertial frames moving at constant speed near c. There is no preferred inertial frame. Both are correct. The paradox is if there are twin astronauts, one in ship A another in ship B. When they meet up who is older?
The original twin paradox is not really a paradox since earth is an inertial frame and the ship is an accelerating frame. Hence the twins can agree who is older.
Maybe it can't, there can possibly be a limit and this should be calculable if we have the correct physics. So maybe our physics is wrong or we do not use what we really know and only seek to prove what we think instead of what we know.
Reply | Report Abuse | Link to thisDear Sir,
Reply | Report Abuse | Link to thisYou have rightly suggested a correction. However, this is valid only if the two bodies are moving away from each other or coming towards each other. If they are moving in any other direction, another correction will be needed. This is obvious. Hence we are not discussing it.
Regards,
basudeba
Dear Sir,
Reply | Report Abuse | Link to thisWe are complementing your observations.
A wave is transfer of momentum without actual permanent displacement of mass. Light being a wave, it must move fastest in "empty" space. Massive particles exhibit momentum, i.e., mv. Thus, its maximum velocity in "empty" space will be reduced proportionately by their mass.
Secondly, Time is the interval between events that orders their sequence. Time measurement is the comparative measurement of this interval with a standard or unit interval that is fairly repetitive and easily intelligible. Light waves being fairly repetitive, can be used as units. But it is not the only unit of time. As long as events, i.e., interaction of forces with bodies, exist, time will continue to exist.
Regards,
basudeba
"When calculating closing speed, you do not apply the Lorentz formula, because you are not changing frames of reference"
Reply | Report Abuse | Link to thisClosing speed is for 3-body scenario. It is a classical concept of speed. It is not the speed between points A and C. It is the speed of point A to B and B to A. Adding these two does not equal speed of A to C. Relative speed is always between A to C. The two ships are all about relative speed. Therefore you can never measure a speed greater than light.
Correction: It is the speed of point A to B and B to C.
Reply | Report Abuse | Link to thisB is in between points A and C. Closing speed is physically meaningless because you can have many points to the left and right of B, add all their speeds and this does not represent any true speed between any point and a reference point.
"1) The dinosaurs will not appear to move faster nor slower because the speed of light is constant regardless of the motion of the observer."
Reply | Report Abuse | Link to thisI think you are confusing the speed of light with the speed of events. Sure the light only travels at light speed, but the motion of the approaching observer means (s)he collects/sees the light from more events than if the observer were stationary.
No wonder kids are screwed up these days. Feeding us cr*p about non-existent, invisible, nasty entities - when the universe works perfectly well without Black Holes! What sort of reality are you 'scientists' living in? I guess it's virtual, Star Wars CGI, fairy story stuff.
Reply | Report Abuse | Link to thisSee the light. Get a real life and join the Electric Universe revolution, where everything works without Dark Forces! w^3.holoscience.com/wp/
No confusion here. That is exactly the point I'm making that's why the images will not appear faster or slower IF the light rays left earth before the ship started traveling. Think about it if you're still confused.
Reply | Report Abuse | Link to thisIs dark matter subject to Einstein's Law, or does the dark stuff play by its own rules?
Reply | Report Abuse | Link to thisI calculate the quantum circulation of Black hole is 3.044x10^-26 m^2/s. where, Planck quantum circulation of particle is 6.36x10^-4 m^2/s. This means that black hole almost unable to radiate energy. The equation of mass of a photon can explain this nature of black hole. This equation is applicable to all fields from particle to the universe written in my book Complete Unified Theory ( pages-424, 1998). There is no such possibilities to collapse the universe by black hole in near billion of billions years.
Reply | Report Abuse | Link to thisNirmalendu Das.
Dated: 03-02-2013.
I calculate the quantum circulation of Black hole is 3.044x10^-26 m^2/s. where, Planck quantum circulation of particle is 3.6369x10^-4 m^2/s. This means that black hole almost unable to radiate energy. The equation of mass of a photon can explain this nature of black hole. This equation is applicable to all fields from particle to the universe written in my book Complete Unified Theory ( pages-424, 1998). There is no such possibilities to collapse the universe by black hole in near billion of billions years.
Reply | Report Abuse | Link to thisNirmalendu Das.
Dated: 03-02-2013.
If you read the advantages of Complete Unified Theory, then you will get the idea about the nature or the Universe.
Reply | Report Abuse | Link to thisMOST IMPORTANT ADVANTAGE OF COMPLETE UNIFIED THEORY (TOTAL PAGES – 424, PUBLISHED IN THE YEAR 1998, ISBN: 81-7643-0005), WRITTEN BY Nirmalendu das. EMIAL: nirmalgopa@gmail.com , Mob: India 9475089337.
1) THE COMPLETE UNIFIED THEORY FOLLOWS THE LAW OF NATURE OR PHYSICS. THIS IS SINGLE THEORY.
2) THIS THEORY IS THE THEORY OF CERTAINTY, THEORY OF EVERY THINGS ETC.
3) THE COMPLETE UNIFIED THEORY IS VERY CLEAR AND EASY THEORY TO UNDERSTAND THE VAST SCIENCE. IT IS POSSIBLE TO DESCRIBE WHOLE SCIENCE WITHOUT USE OF CALCULUS LIKE MATH.
4) IT IS POSSIBLE TO KNOW DIFFERENT FINDINGS FROM PARTICLE TO THE UNIVERSE BY THIS SINGLE THEORY.
(THE CALCULATED RESULTS ARE EXACTLY TALLIED WITH THE FINDINGS OF OTHER TRADITIONAL THEORIES DONE BY THE SCIENTISTS IN THE DIFFERENT FIELDS OF SCIENCE.)
5) THE COMLLETE UNIFIED THEORY CAN EXPLAIN THE INTERNAL MECHANISM OF MATTERS DURING EMISSION OF ENERGY. IT IS NOT POSSIBLE TO KNOW FROM THE TRADITIONAL THEORIES. FOR EXAMPLE, WE DO NOT KNOW THE INTERNAL MEHCANISM OF THE EINSTEIN`S EQUATION E = mc2 THAT, IN WHAT WAY MATTER IS RADIATING ENERGY AS m IS NOT ALONE .
6) THIS THEORY CAN SOLVE THE STRUCTURE OF ELECTRON, ELECTROMAGNETIC RADIATION, BIRTH OF MAGNETISM, MAXIMUM MASS OF THE UNIVERSE, THE SUCCESSIVE DERIVATIVES OF BIRTH OF STARS, GALAXIES, QUASARS, PARTICLES ETC, THUS THE UNIVERSE.
7) IT DOES NOT AGREE WITH THE DISTASTEFUL CONCEPT OF SCIENCE LIKE ZERO REST MASS OF THE PARTICLES (MASS OF PHOTON, GRAVITION).
8) THE VALUE OF Pi (π) IS NOT CONSTANT AT EXCITED STATE OF MATTER WHEN PARICLE IS DEFORMED ------ BUT THE SCIENTISTS ARE USING THE VALUE OF π AS CONSTANT IN EVERY FIELDS WHERE NEEDED.
9) THE COMPLETE UNIFIED THEORY DO NOT AGREE WITH THE EQUATION OF THEORY OF RELATIVITY OF EINSTEIN OF MASS, AS VELOCITY IS NOT MASS, THAT CAN INCREASE OR DECREASE THE MASS. THE VELOCITY IS ONLY THE ENVONRMENT THAT CAN INCREASE THE MASS BY ACTING MASS TO MASS REACTION.
10) THE COMPLETE UNIFIED THEORY CAN EXPLAIN THE MASS OF CURIE PARTICLE (TILL UNKNOWN) WHICH IS RELATED TO ALL SUBATOMIC PARTICLES EVEN HIGGS BOSON, QUARKS. THIS IS VERY NEW SYSTEM, IN WHAT WAY ALL PARTICLES ARE INTERRELATED.
11) COMPLETE UNIFIED THEORY IS SINGLE THEORY. WE CAN SOLVE ALL TO USE THIS THEORY.
12) THIS THEORY CAN GIVE THE ANSWER THAT WHY BLACK PARTICLE, BLACK HOLE ETC. LOT OF THINGS IS THERE.
Nirmalendu Das.
Muons have a very high relativistic mass/energy level relative to absolute space (207 times that of an electron)and very high velocity (kenetic/energy - nearly the speed of light) relative to other bodies so it just takes longer to dissapate this kenetic energy and mass/energy.
Reply | Report Abuse | Link to this"If a black hole's event horizon gets bigger every time its density gets bigger, i.e., it "absorbs" mass, why hasn't the whole universe collapsed into an enormous black hole yet? Shouldn't this kind of expanding black hole be getting bigger exponentially? And will this be the end of our universe and possibly the birth of a new one (or where ours began—a big bang)?"—Shaido666
Reply | Report Abuse | Link to thisBlack Holes lose mass via Hawking's radiation.
A photon of light can be influenced by the gravity of a galaxy and have its trajectory bent from it original path of travel. Could that same photon of light be slowed by the gravity of the galaxy it is leaving particularly if the home galaxy is far more massive?
Reply | Report Abuse | Link to thisTests of the theory of relativity have shown that a photon always travels at the same speed, which is called c = 299 792 458 m/s. In a gravitational field, the frequency of the light may change, due to space-time distortion by gravity, but the speed remains constant.
Reply | Report Abuse | Link to thisHere are some questions that I hope George Musser, and friends will answer:
Q1. Should light go into orbit around a massive star (black hole?) if the orbital velocity = c?
Q2. Does a gravitational wave (GW), which is itself a spacetime distortion, pass unaffected through a strong gravitional field like a white dwarf?
and finally,
Q3.If a GW and photons (a gamma ray burst -GRB) are created by an event on a massive star, could the GRB photons take longer to travel from the event than the GW due to their interaction with the gravitational field of the event?
How come light travles with the fastest possible speed? In other words how can we know this?
Reply | Report Abuse | Link to thisWe are actually inside a black hole. A black hole with the mass of the universe will have an event horizon roughly the size of the universe
Reply | Report Abuse | Link to thisNever heard that theory, very cool. However it is my understanding that the universe is expected to die a cold death of expansion, not the hot death of contraction?
Reply | Report Abuse | Link to thisNever heard that theory, very cool. However it is my understanding that the universe is expected to die a cold death of expansion, not the hot death of contraction?
Reply | Report Abuse | Link to thisImagine a balloon expanding at light speed in all directions. The distance of opposite edges of the balloon is growing faster than light, but no objects within the balloon are.
Reply | Report Abuse | Link to thisI saw a few days ago a Nova program about the search for absolute zero...is there one for the opposite temperature? What is the temperature as one increases one's light speed?
Reply | Report Abuse | Link to thisTake 200 billion galaxies in the universe with 200 billion suns each and you get a mass of the universe of about 8x10^52 kg. Take that mass and a radius of 1.3x10^26 m (14 b.l.y.) and you get an escape velocity equal to something close to c. If the escape velocity really is c this mean that our own universe is already a black hole.
Reply | Report Abuse | Link to thisI'm having trouble envisaging where the concept of a singularity is in that universe black-hole?
Reply | Report Abuse | Link to thisIf you look at the equation for escape velocity, you see a mass divided by a radius. We normally think of a fixed mass and divide that by a very small radius to bring the escape velocity up to the speed of light. But for all of the galaxies spread uniformly throughout the universe, mass goes up as the cube of the radius. So you end up with an escape velocity that rises linearly with radius. For a radius as large as the universe you can get an escape velocity as big as the speed of light.
Reply | Report Abuse | Link to thisSure, but classical physics says there is a singularity at the centre of a black hole. The universe on the contrary is spread out within the event horizon and if anything is expanding rather than converging toward a singularity. So it doesn't comply with the classic definition. Now I'm not saying the classic definition has to be right - just that your attractive idea doesn't quite fit it.
Reply | Report Abuse | Link to this