Astronomy-Interesting Facts

[youngyew]

In the absence of oxidant (e.g. oxygen), you will most probably melt / denature instead of burn when you are heated up.

[vseehua]

Originally Posted by youngyew

In Einstein's frameworks, nothing can travel faster than light. However, nobody really says that nothing exists outside Einstein's framework, so who knows, one day it might be possible?

But of course I am not qualified to talk about this thing, just some random ramblings here.

In Einstein's frameworks, there is nothing that prevents anything from travelling faster from light. It just states that we cannot ever accelerate from 0 to the speed of light. However, it doesn't state that an particle cannot travel natively faster than light.

Originally Posted by Al-Bert

I could comprehend why Sun could "burn" without oxygen gas...

However, I have no idea why something would get burned when it travels close to the Sun? ( There's no any kind of gas particle exist in outerspace )

That is burning in the sense of combustion. In the case of something burned while being close to the sun, it is refering to the melting-evaporating-plasmafication of matter/destruction of chemical bonds when it gets too heated because of the heat radiating from the sun's surface...

Originally Posted by Al-Bert

Wanna ask something, light beam has the speed of 300000 km/s....
Do you think the speed of light beam will increase when we shoot the light beam in a constant velocity moving vehicle?

Let say if the velocity of the vehicle is 200km/s....will the speed of light beam shot from the vehicle increase to 300200 km/s ?

When you move, your time actually slows in relative to your surroundings, which makes it possible for light to stay at a constant speed however fast that you are moving.

It had been tested in the 70s by putting an atomic clock on a concorde and one on the surface of the Earth. The one on the concorde is a tiny bit slower than the one which is on the surface of the Earth but still measurable to an extent.

Strange as it sounds, but that is some of the most accurate predictions that General Relativity had predicted to date...

[bluez_aspic]

Originally Posted by vseehua

In Einstein's frameworks, there is nothing that prevents anything from travelling faster from light. It just states that we cannot ever accelerate from 0 to the speed of light. However, it doesn't state that an particle cannot travel natively faster than light.

There are such hypothetical particles known as tachyons, but even if they were to exist information would still not be transmitted faster than the speed of light. General relativity reduces to special relativity in a local sense, but I've routinely read articles (usually re: big bang) which claims that the equations permit space to expand in such a way that two objects, located at a great distance apart, can have a recession velocity greater than the speed of light. Note that this refers to an expansion of space, not motion through space - so Special Relativity is not violated.

(to see this space expansion thing - assume that the universe expands in such a way that its size is doubled every 1 year. So two planets A and B which were initially, say, 5 light years apart, would now be 10 light years apart. But this took place in the time span of only 1 year. So from the perspective of A, planet B would have receded much faster than the speed of light)

Most 'faster-than-light' phenomena involves 'cheating' in some sense - but information still is not transmitted faster than light. If that were to be the case, cause-and-effect would be literally turned upside down - one immediate consequence would be that the laws of physics would appear different to different observers. Terrible indeed, but so far we have no reason to conclude otherwise.

Originally Posted by vseehua

When you move, your time actually slows in relative to your surroundings, which makes it possible for light to stay at a constant speed however fast that you are moving.

This isn't quite accurate, actually. One of the fundamental postulates of Special Relativity is the universality of the speed of light - that whatever you do, whether you were to travel fast or slow or remain motionless, light will always travel at the same speed. It's taken as an AXIOM, a FUNDAMENTAL TRUTH - and so far that has been well corroborated by experimental evidence.

It's weird and mysterious, isn't it? A good way to understand this is to try comparing the speed of light (which is independent of both source and receiver), to the apparent speed of a ball (which depends on both the speed of the source and receiver), and the way in which sound travels (independent of the speed of the source, but dependent on the speed of the receiver relative to the medium).


re: Al-Bert - If you're serious about picking up Special Relativity, it's actually quite easy (only requires knowledge of Pythagoras' theorem and elementary algebra) - Halliday, Resnick and Walker has a chapter or two dedicated to a gentle introduction on the subject. Special Relativity by A.P. French. is more hardcore, but that happens to be my favourite text.

[vseehua]

Originally Posted by bluez_aspic

This isn't quite accurate, actually. One of the fundamental postulates of Special Relativity is the universality of the speed of light - that whatever you do, whether you were to travel fast or slow or remain motionless, light will always travel at the same speed. It's taken as an AXIOM, a FUNDAMENTAL TRUTH - and so far that has been well corroborated by experimental evidence.

It's weird and mysterious, isn't it? A good way to understand this is to try comparing the speed of light (which is independent of both source and receiver), to the apparent speed of a ball (which depends on both the speed of the source and receiver), and the way in which sound travels (independent of the speed of the source, but dependent on the speed of the receiver relative to the medium).


re: Al-Bert - If you're serious about picking up Special Relativity, it's actually quite easy (only requires knowledge of Pythagoras' theorem and elementary algebra) - Halliday, Resnick and Walker has a chapter or two dedicated to a gentle introduction on the subject. Special Relativity by A.P. French. is more hardcore, but that happens to be my favourite text.

Well, i am trying to put it in a way that more people can understand what is going on Something like the electronic shells in the atoms taught during our SPM years

[Al-Bert]

Is black hole a kind of wormhole?

And if no light could escape from black hole ( means we can't see black hole ), then how come Hawking radiation from the black hole could be observed?

[bluez_aspic]

Originally Posted by Al-Bert

Is black hole a kind of wormhole?

And if no light could escape from black hole ( means we can't see black hole ), then how come Hawking radiation from the black hole could be observed?

My memory is rather fuzzy on this one, but I'll give it a shot:

A wormhole is two separate black holes being connected by a 'tunnel' (in the fabric of space-time) - but it's more of a sci-fi concept, really. The existence of black holes on the other hand rests on a sounder basis, since the equations of General Relativity predicts their existence - whether they truly exist is another thing altogether. I'm not quite sure what the consensus is nowadays.

Hawking radiation is emitted from a black hole due to a quantum mechanical effects (the Heisenberg uncertainty principle, to be precise). Primordial black holes (i.e. those which were formed in the infancy of the universe) could emit more Hawking radiation than they suck in, and thus this would enable primordial black holes to be observed. But it's said that the emitted radiation would be very weak, so not much success in verifying this one either.

[vseehua]

Observations have proved that black holes do exist in the universe... so far, because of the limits of certain extreme conditions like a glaxy being able to hold it's mass or matter (stars, materials) together.

A wormhole, however, is a hypothesis that have not yet been proved, or calculated to a convincing extent. This will be the reason why i would call it hypothesis. Wiki article here.

More about Hawking Radiation here. Notice that the radiation doesn't really come from inside the hole, rather, just above the event horizon. So the statement about things needing to travel more than the speed of light to excape a black hole still holds.

[Al-Bert]

I understand that the formula to calculate the wave energy is E=hf, where E is energy, h is Planck contant and f is frequency of wave.

My doubt : wouldn't the amplitude of the wave bring any effect to wave energy? I mean, you need work in order to increase the intensity of a wave, thus don't you think that the work done will be converted into the new energy of the wave? But the formula E=hf doesn't seem to endorse it.

[youngyew]

The E=hf formula is for the energy of a single photon. Amplitude of a wave reflects the number of photons, but it doesn't affect the energy contained in each photon.

[ChristopherCWL]

Anything to do with the E=MC^2 formulae??