# heres a stumper...Question

Discussion in 'Physics & Math' started by HEXiT, Dec 11, 2011.

1. ### SarkusHippomonstrosesquippedalo phobeValued Senior Member

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9,437
If by spacetime you mean our Universe, then it is increasingly considered to be flat (http://www.universetoday.com/37029/flat-universe/) but that does not mean that it will collapse in on itself... quite the opposite... the universe will keep expanding, and the fate will likely be heat death / big-freeze where everything has the same temperature and no useful work can be carried out. Another scenario could be that the acceleration of the expansion becomes too much for EM and gravity, and everything breaks down to a thin soup of the most basic of building-blocks etc.
A flat universe will not collapse in on itself.

3. ### Crunchy CatF-in' *meow* baby!!!Valued Senior Member

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8,423
What you stated doesn't really make sense.

5. ### HEXiTRegistered Member

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37
objects only have velocity when moving in relation to something else that it can affect so if everything is moving at the same speed then in relation to each other they have no velosity as the object cannot accelerate or decelerate in relation to any other body around it. so everything will come to a stop.
picture throwing balls into a bucket while your on a moving train. the bucket and the train represent space time (our Hubble bubble as some1 so sweetly put it) you stand and throw the ball it accelerates to the point where it makes contact with the bucket and thus becomes part of the train now throw the second ball and like the first ic caught in the bucket. the ball is now part of the train but in relation to the other ball it is now stationary even though there still moving with the train...
now take the balls and make em matter/energy and the train space and time...
now stretch the train and everything in it including the bucket with the two balls in.
would the balls resist the stretching and thus conform to a constant speed of light or would the balls stretch too and in doing so break a fundamental law..

i do understand what happens if the objects in the train were traveling less than the speed of light, but thats not what im asking about...

im sorry im dyslexic so cant always precisely express what im thinking in words.
(this isnt an excuse its just a fact, so dont let that sway you if you think my musings are a brain fart)

7. ### DinosaurRational SkepticValued Senior Member

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4,885
The equations relating to tacyons require that they move backward in time. This results in the following paradox.
Suppose a group of scientists built a tacyon generating device, which they intend to turn on at exactly noon.

The device requires a huge amount of power. When they detect the tacyons some time prior to noon, they decide to not turn on the generator. Why use all that power when they know the device works & their theory is correct?​
BTW: I think that circa 1955-1965, building a tacyon generator was considered to be a worthwhile project. Martin Gardiner pointed out the paradox in his Scientific American Mathematical Games column & the project never got started.

Current cosmology considers the following to be valid.
The expansion of the universe is such that the farther an object is from an observer, the faster it is receding.

The relationship between distance and recession speed is such that there is a distance at which the recession rate is equal to light speed. Beyond that distance objects are receding faster than light speed.

Objects up to the the critical distance are viewed as being in the observable universe. The observable universe is different for different observers.

An observer cannot have a cause/effect relationship with any object beyond the critical distance.​
I think that the velocity of light limit on speed is actually a limit on the possibility of interaction.

BTW: As a galaxy approaches the critical distance, the red shift makes its apparent brightness dimmer & dimmer. At the critical distance it is so dim that it cannot be seen.

8. ### DaleGeriatric friend of trollsRegistered Senior Member

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There are heretics who dare doubt an accelerating cosmos. Many dare not admit that crime. Anyhow, if a constant force were pushing or pulling anything in any particular direction, it seems that Albert E. threw in an increase in mass for velocity increase, mathematically precluding more than mere approach to the speed of light if such speeders were of any mass at all. Seems like mass gets to infinity as velocity reaches c. By then it is time to give up.

9. ### Telemachus RexProtesting Mod StupidityRegistered Senior Member

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"Speed" and "velocity" are slightly different in that speed is a scalar value, whereas velocity is a vector. In fact if two objects are moving at the same speed in different directions, they will have different velocities and be will be moving relative to one another.

Let's assume, hypothetically, that every galaxy were accelerating away from us at greater than the speed of light, then they would be moving relative to us, and would (by the assumption we started with) have a velocity relative to us. If they were moving that fast, though, we would slip outside our "light cone" at which point we would no longer be able to see them. Whether we can see them or not, at least according to classical physics, they would still be moving relative to us.

10. ### Jack1941Registered Member

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12
Wow, I have a lot of issues with a statement that declares a declaration as fact, just to support its validity. The things you declare are fact are indeed not fact, nor are the true. If this subject is going to go any where, start over, and state what you suppose might be true, and declare it a possibility. We can bring enlightenment to this Forum, and possibly achieve a consensus of opinion. But we need to take it slow enough to allow those to grow, that will.

11. ### Jack1941Registered Member

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Are we referring to the section from 400 nm to 700 nm of the electromagnetic wave spectrum when we refer to light? And any discussion of the vectoring velocity is meaningless in a physical sense. And any fundamentally hypothetical statement is not valid. The propagation of EMF with respect to the particle from which the EMF emanates from is the only way to have a valid expression of the speed of light. Any other representation for the speed of light is not valid. Can we establish truths and remain within those confines? Please do.

12. ### James RJust this guy, you know?Staff Member

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36,948
That's wrong. There's no speed-of-light limit on how fast space can expand.

In this thread, we're referring to the section from 0 nm to infinite nm.

What's a vectoring velocity? And who discussed it?

Why?