Am no expert, but let me try...
1. Einstein never said nothing can move as fast/faster than light. He said nothing can
accelerate to the speed of light.
As an object accelerates, its mass increases, its length decreases along the direction of its travel, and time slows down for that object. These are all real and measured effects. If you extrapolate the measured effects forward, you find that when an object's speed is approximately 300,000 km/s, its mass becomes infinite, its length becomes zero, and time screeches to a halt for that object. Accelerating to that speed would therefore be a theoretical impossibility.
Let's consider the issue of mass. In order to accelerate an object, you have to apply a force. The amount of acceleration is directly proportional to the force, but INVERSELY proportional to the object's mass. In other words, as the object gets heavier, it accelerates less. That's Newton's second law in a nutshell.
As an object approaches the speed of light, its mass increases. This was predicted by Einstein and borne out by experiment. As the mass increases, it takes more and more energy to accelerate it further. If the object were ever to reach the speed of light its mass would become infinite; therefore, it would require infinite energy to get it to that point. Since infinite energy isn't available, it's impossible for anything with mass to reach the speed of light.
The only reason that light can travel at the speed of light is because it doesn't have mass. Light does carry energy, which can be converted to mass, but not mass itself.
Lorentz factor, gamma, (recall, for a moment, γ = 1/√(1-v²/c²).) needs to be brought in to E=Mc² to understand it properly.
Also recall that E=γ*mc², and this provides the *total* energy (kinetic+static) for a particle in motion. Suppose that you take some random particle, with mass m>0. Then you try to fling it around at some speed, v. Plug in some numbers and take the limit as v>c. What happens? γ>∞. What does this imply? As you get arbitrarily close to the speed of light, your energy required to accelerate any further is infinite. This isn't one of those small infinities that we can make go away with a special math trick... it is a literal infinity. You would literally need more energy than exists in the Universe to take any particle of mass m>0 to the speed of light. This is why the only particle that travels at the speed of light is photons, they have m=0 (not something close to 0, exactly zero).
BTW... As for mass increasing to infinity (the common notion), this is the wrong way to think about it. Your mass doesn't actually increase. Text books sometimes simplify the equation to E=Mc², where M = γ*m. it works mathematically but physically its just wrong.
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2. Ok, we are dabbling in the realms of speculation here... The big bang theory (expansion from singularity theory) is steadily getting replaced by the big bounce theory (alternating expansion from and contraction to a singularity).
A black hole is a region of spacetime with enormous (not infinite) density (with some volume... it is a dead star after all) from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently dense mass will deform spacetime to form a black hole.
All the genesis theories on the other hand talks about a singularity. Singularity is 0D. It is a point in spacetime in which gravitational forces cause matter to have an infinite density and zero volume.
So, yeah, a bit after the big bang, things might have been similar to a Black Hole as the singularity lost density and gained volume. However, it would be a really weird kind of black hole as there is no other source of light/mass/existence of anything else present at the time as a frame of reference, as everything in the universe is within the expanding singularity.
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3. Photons can travel at c (speed of light) because it has 0 mass.
The light enters the material and hits atoms of that material, which absorb and then re-emit photons this effectively 'holds back' the light for a instant and then it carries on. The denser the material, the more often this happen and so the slower light can travel.
When atoms absorb a photon of light, it is actually the electrons of the atom that do this – they rise into another energy state (i.e. temporarily take the photons energy) and then drop back down (releasing the photon in a sense).
The confusing part for me is that light isn't a stream of photons necessarily – it is a wave in the electromagnetic field. Photons are just a good way of explaining this setup. It is the energy of this wave that is absorbed released and not a photon itself.
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A few questions that occurred to me recently. Let's see if any science experts here can answer them!
1. FTL travel is not possible according to Einstein. But is it possible to travel at the speed of light? According to Einstein, at the speed of light, time stops so does that mean someone travelling at light speed could instantaneously travel to the edge of the universe and back to earth?
2. Black holes are bodies with such enormously high mass in such a tiny space that they have incredibly high gravitational pull. A few nanoseconds after the Big Bang, this was exactly the state the universe was in, so was it a black hole? Is the universe actually a massive black hole?
3. Why do photons travel at the speed of light? We know that photons travel slower in glass than in vacuum (2/3 * c) so if a stream of photons enters glass and decelerates to 2/3 *c, when it gets out of the glass, what causes it to accelerate again? Is it getting some energy boost from somewhere?
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