« on: Yesterday at 05:04:15 »
Yes. Recall Hawking Radiation.
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Accelerating objects radiate.Only charged particles radiate, unless you're talking about gravitational waves?
m×c2 – 2×G×m×M/r = 0 (we have to count the gravitational term twice because each body exerts on the other, I think...)I disagree. The potential energy is for the system of two particles in this case so you don't need the two.
Temperature is a form of kinetic energy (largely), and therefore we would expect a mass of warm air to cool as it rises, as the kinetic energy of its temperature gets exchanged for potential energy of its height (and this is typically what is observed).Excellent response. My compliments to the chef!
This states that L = V + U.Correction. L = T - V, where T = Kinetic energy and V = Potential energy. If the potential is a velocity dependent one then the letter U is used. This is particularly important in electrodynamics.
Don’t be derailed by the concept of a singularity. Chris Baird says of singularities:
“In general, singularities are the non-physical mathematical result of a flawed physical theory. When scientists talk about black hole singularities, they are talking about the errors that appear in our current theories and not about objects that actually exist.”
I think it is worth keeping in mind that the same would apply to a BB singularity.
So the universe acording to the theory has been infintively small at one point.MAY have been.
Chris Baird, again:
“….infinities never exist in the real world. Whenever an infinity pops out of a theory, it is simply a sign that your theory is too simple to handle extreme cases.
I have no problem with the assertion that the balance of energy in the Universe is zero.See: http://www.newenglandphysics.org/ask_a_physicist/guth_grav_energy.pdf
However, I find myself wondering if that is actually the same as saying the total amount is zero.Seems to be a matter of semantics to me.
If there is x amount of +ve energy, that is an amount.What does "+ve energy" etc mean? I never saw that term before.
If there is x amount of -ve energy, that is an amount.
Since nothing can move faster than light that has to be the upper limit, if not something else already limits it.Welcome to the forum!
That's where I have a problem with the big bang theory because the theory revolves around the universe expanding from a single point aka a singularity. So the universe acording to the theory has been infintively small at one point. Since energy cannot be created, there has to be the same amount of energy in the universe from the point of the big bang to now.That is incorrect. There is the same amount of energy before the big bang as there is now. The total amount of energy in the universe is zero. That's how energy remain conserved as it was created. There's two kinds of energy; positive and negative. Negative energy comes from gravitational potential energy and positive energy comes from particles. You can read about it in The Inflationary Universe by Alan Guth. I can make those pages available to you if you'd like?
What part of differential geometry do you suspect I do not understand. I assume you talking about grads divs and curlsNo. That's vector calculus. The basics of differential geometry are described here:
Thanks folks for the answer to my original question.The term "big bang" is misleading. It makes it appear as if within the theory itself there is an event which started the universe expanding. There may have been such an event but we have no way to adduce it as of now.
I get the super nova example but not the- We don't "look back" to the big bang as if it happened a long distance away. In a sense it happened everywhere..... HELP!!!!
This, from Stephen Whiston - @whizzer666 - on Twitter today:We don't "look back" to the big bang as if it happened a long distance away. In a sense it happened everywhere.
"I have always not been able to reconcile the fact - nothing is faster then the speed of light - yet we look back to the big bang through our telescopes - honesty how does that work? Can you explain?"
Who can help with this?
In a box falling freely it is said there is no experiment that can determine we are in motion. If we are in a very large box we could use rubber balls thrown at the walls. Gravity will change the kinetic energy of the balls. It will slow this moving away from the source. This change in inertial motion will indicate freefall towards the source of the gravitational field.It depends on stature if the field. If the field is uniform then no. Otherwise yes. Simply bring a gradiometer with you and you can make that determination.
If a photon is at point p1 at time t1 and later is at point p2 at time t2 how far has it actually travelled? "With respect to whom?", you ask. Is that the wrong question?That depends on whether the spacetime is curved or not.
Ah... I see now that Jeffrey was talking about relativistic conditions, where inertial mass is not a constant.On the contrary. Newton's Laws are still valid. It's a common misconception that Newton defined F = ma. That was a relation proposed by Euler, not Newton. Newton defined force, essentially, by F = dp/dt. And his third law always holds when the forces are contact forces.
But under relativistic conditions, an object no longer obeys Newton's laws
- or you have to bend F=ma to say that m varies with velocity or gravitational potential - and that the time you use to measure acceleration also changes.
- these are not modifications that Newton would recognize!When used correctly, sure he would.