Back to Home

Blackholes2 Forum Message

Forums: Atm · Astrophotography · Blackholes · Blackholes2 · CCD · Celestron · Domes · Education
Eyepieces · Meade · Misc. · God and Science · SETI · Software · UFO · XEphem
RSS Button

Home | Discussion Forums | Blackholes II | Post
Login

Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place...
The Space and Astronomy Agora
Time Dilation Explained In Illustratory Fashion...

Forum List | Follow Ups | Post Message | Back to Thread Topics | In Response To
Posted by nåte/">nåte on October 6, 1998 05:51:15 UTC

: Good point nate, I've heard that too about black holes (and it seems to make sense). I have a request for you, you seem an intelligent person from your excellent posts, well informed and all that. I have an extreme interest in the whole advanced physics field, and I have never heard the term "time dilation" until you ealier post. I am very interested in this, but I must say I don't think I completely understood it. Could you possibly rephrase your explanation, that is explain it in a different way? If you could I would very much appreicate it. Thanks.

: -Paul

: : : When real physical objects become black holes, the light they emit to distant observers becomes highly redshifted as the event : : : horizon size is approached as seen by distant observers. The details can be found in 'Gravitation' written by Misner, Thorne and : : : Wheeler . As the surface of the star reaches the horizon, its light is infinitely redshifted. In the reference frame of the star's surface, as it just passes the horizon radius, it has emitted a finite number of photons just : : : outside of the horizon, and it is these that may escape to distant observers. The problem is that they are increasingly redshifted : : : as the surface emitting them gets closer to the event horizon. In the limit, the last photon is almost infinitely redshifted. Also, : : : gravitational time dilation occurs so that the interval between the emission of each photon lengthens dramatically as the event : : : horizon is approached, and the intensity of the light exponentially decreases in time. The net effect is that to the outside : : : observer, the surface of the star fades within a few seconds and its wavelength of peak emission shifts from X-ray to optical : : : energies, all the way out to infrared and radio wavelengths. X-ray astronomers recently discovered just this fading effect in the : : : X-ray light from a black hole a few thousand light years from Earth.

: : : The view is completely different from the reference frame fo the star. Nothing weird happens when the surface crosses the : : : event horizon radius. Even the view out into distant space may be unchanged except that incoming light get highly blueshifted as : : : it falls down the gravitational well of the black hole and passes the horizon. But, after passage, no light can escape the hole, and : : : furthermore, the mathematics show that no stable orbits are possible inside. Space-time itself is collapsing.

: : The only problem with this whole concept is the fact that (from the stars frame of reference) while observing the outside universe while approaching the horizon, time exponentially speeds up before our eyes till ultimately at the instant of entering the horizon the universe rapidly comes to its end! So, given this reasoning (from the stars reference point), how could anything ever enter a black hole within "our" time/space continuum? The whole concept of a black hole (starting at the event horizon) should realistically be explained that they do not and cannot exist within our dimension. And if you challenge this concept, keep in mind the fact that any mass entering into this gravity well is also exponentially time dilated to the point of infinity... Not just from our reference frame, but from the object falling as well.

sure paul... : ) and thank you.

First, one has to visualize the dimension of time and space as an entity beyond nothingness. It is true that space is nothing, and besides itself holds nothing. However, a way to visualize time and space is to observe how the effects of gravity and velocity reveal its very nature. What a better way to observe "nothingness" than to observe two, if you will, "recipricols" of time/space.

Lets start with gravity. The phenomenon of gravity is quit amazing in fact. The force that a mass has among another mass is that of attraction to eachother. One can visualize this in a two dimensional field by assuming a rubber sheet suspended in air being held at the four corners of the mat. place a heavy ball or object in the center and notice the distortion the "mass" has on the mat. (space time) If you were to place a smaller mass near this depression it would "pull" towards the center of the mass. the key thing here is 'center' of the mass. gravity always has its point of origin from the center. One can see how this relates to, and is reality in our dimension of time and space. The effect is there.

Now, where does time and velocity come in here? Well, imagine a grid of lines inscribed on that rubber mat. If there is a mass present those lines that form a grid are now quite distorted. (depending on the amount of gravitation...) Now the concept of time comes in... Imagine time moving at the speed of light traveling on those lines on the mat. Without the presence of gravity the lines seem straight. In the presence of gravity the lines seem distorted, right? well in fact they are, but it depends on what frame of reference you are observing. Imagine you are an observer from the "straight" line area observing the "curved" space/time far away. well, when light (which remains at a constant velocity (c)) is traveling along the "curved" portion of time/space it appears to takes longer for it to travel the same "apparent" distance from your perspective. Now on the same note, say you were observing light travel on the "straight" portion of space/time, from the "curved" portion of time/space. Well, the "apparent" time it takes for the light to travel on the straight path seems to go faster; thus time dilation in both instances.

Now, time dilation is not limited to gravitational forces... it also is related and affected by velocity.. If you could approach the speed of light, time and space would become more and more curved; until eventually space and time would be infinitely curved. this, however, would only be possible if one could achieve the velocity of light. thus the effects of time dilation are apparent in velocity factors as well.

there are other factors that happen in both gravitional and velocity time dilation as well. Like length contraction, mass increase, ect. However, these are all apparent increases. They are only observable from someone observing from a stationary reference. It is interesting to note that given that these effects (mass increase) are apparent to the stationary observer, how these "affect" the traveler are quite apparent. Thus the reason it is impossible to reach the speed of light, due to theoritical mass increase. Even though if you were to observe your own space craft traveling this speed you would notice no mass increase or length contraction, just you would notice the ever increasing need of energy to accelerate at an exponential rate.

Note: You would observe, looking at the outside universe, time and space "becoming" infinitely curved, till eventually (if you could travel (c)) time would stop, this dimension would be gone... But your apparent mass would be infinite and your apparent volume... zero. :)

I hope this will clarify or illustrate for you. I choose visual exzamples because this is the way I think and visualize much of physics.

take care...

Follow Ups:

    Login to Post
    Additional Information
    Google
     
    Web www.astronomy.net
    DayNightLine
    About Astronomy Net | Advertise on Astronomy Net | Contact & Comments | Privacy Policy
    Unless otherwise specified, web site content Copyright 1994-2020 John Huggins All Rights Reserved
    Forum posts are Copyright their authors as specified in the heading above the post.
    "dbHTML," "AstroGuide," "ASTRONOMY.NET" & "VA.NET"
    are trademarks of John Huggins