You Can't Travel Back in Time, Scientists Say

Png_Prince · Post time 29-4-2007 01:04 PM

The future of time travel

Various researchers have proposed ways in which backward and forward time machines can be built that do not seem to violate any know laws of physics. Remember that the laws of physics tell us what is possible, not what is practical for humans at this point in time. The physics of time travel is still in its infancy. While all physicists today admit that time travel to the future is possible, many still believe time travel to the past will never be easily attainable. Don't believe anyone who tells you that humans will never have efficient technology for backward and forward time travel. Accurately predicting future technology is nearly impossible, and history is filled with underestimates of technology:

"Heavier-than-air flying machines are impossible." (Lord Kelvin, president, Royal Society, 1895)

"I think there is a world market for maybe five computers." (Thomas Watson, chairman of IBM, 1943)

"There is no reason for any individual to have a computer in their home." (Ken Olsen, president, chairman and founder of Digital Equipment Corp., 1977)

"The telephone has too many shortcomings to be seriously considered as a means of communication. The device is inherently of no value to us." (Western Union internal memo, 1876)

"Airplanes are interesting toys but of no military value." (Marshal Ferdinand Foch, French commander of Allied forces during the closing months of World War I, 1918)

"The wireless music box has no imaginable commercial value. Who would pay for a message sent to nobody in particular?" (David Sarnoff's associates, in response to his urgings for investment in radio in the 1920's)

"Professor Goddard does not know the relation between action and reaction and the need to have something better than a vacuum against which to react. He seems to lack the basic knowledge ladled out daily in high schools." (New York Times editorial about Robert Goddard's revolutionary rocket work, 1921)

"Who the hell wants to hear actors talk?" (Harry M. Warner, Warner Brothers, 1927)

"Everything that can be invented has been invented." (Charles H. Duell, commissioner, US Office of Patents, 1899)

Wouldn't it be a wild world to live in if time travel devices played important roles in the development of humanity條ike the computer and the telephone? Mathematicians dating back to Georg Bernhard Riemann (1826-1866) have studied the properties of multiple connected spaces in which different regions of space and time are spliced together. Physicists, who once considered this an intellectual exercise for armchair speculation, are now seriously studying advanced branches of mathematics to create practical models of our universe.

Science-fiction stories about space travel have already inspired humans to travel to the moon. Similarly, will time-travel stories inspire us to create real time-travel mechanisms? Will we ever find a way to overcome the Einstein speed limit and make all of spacetime home?

I wonder what humanity will discover about spacetime in the next century. Around four billion years ago, living creatures were nothing more than biochemical machines capable of self-reproduction. In a mere fraction of this time, humans evolved from creatures like Australopithecus. Today humans have wandered the moon and have studied ideas ranging from general relativity to quantum cosmology. Who knows into what beings we will evolve? Who knows what intelligent machines we will create that will be our ultimate heirs? These creatures might survive virtually forever, with our ideas, hopes, and dreams carried with them.

There is a strangeness to the cosmic symphony that may encompass time travel, higher dimensions, quantum superspace, and parallel universes梬orlds that resemble our own and perhaps even occupy the same space as our own in some ghostly manner. Stephen Hawking has even proposed using wormholes to connect our universe with an infinite number of parallel universes. Edward Witten is working hard on superstring theory, which has already created a sensation in the world of physics because it can explain the nature of both matter and spacetime. By realizing that the fundamental laws of physics appear simpler in higher dimensions, string theory can unite Einstein's theory of gravity with quantum theory in ten dimensions. Our heirs, whatever or whoever they may be, will explore space and time to degrees we cannot currently fathom. They will create new melodies in the music of time. There are infinite harmonies to be explored.

aku_EnSeM · Post time 29-4-2007 01:54 PM

that's interesting....

if i were the mod, i'd give u creadits 4 that....

tadika_action · Post time 1-5-2007 07:36 AM

Originally posted by aku_EnSeM at 27-4-2007 04:55 AM
Emm... i'm not trying to oppose anybody... i'm being neutral rite here, alright??

i'm very interested in this relativity things... but suddenly i found a law (don't know whether it is vali ...

I'll look into that once I'm done with my work. Insya Allah.

I remember solving a lot of paradoxes in my SR class... the broomstick travel in a closed room etc. If Alice Law can amend
some parts in Eistein Relativity theory... it's even better. It took a few centuries for scientists to discover Newtonian physics doesn't
work in a speed-of-light environment,aight?

If you are interested in physics... good for you!

aku_EnSeM · Post time 1-5-2007 10:20 AM

paparock · Post time 18-5-2007 12:28 AM

Aku berpendapat kita boleh bergerak semakin pantas tapi kita tak akan dapat keluar dari masa semasa kita. Maknanya perjalanan merentasi masa adalah mustahil. Kalau nak mempercepatkan masa perjalanan, boleh.

Kita kena ingat tenaga tak boleh dilenyapkan. Ia hanya boleh berubah dan berubah dan berubah tanpa henti akibat faktor kimia, fizik dan sebagainya.Jadi kalau kita boleh reverse setiap proses perubahan tu maka kita boleh tiba di mana2 titik peristiwa yang kita nak, but still we have no choice but to go along the path yang kita dah lalui aje. Dan untuk tujuan itu juga rekod kita perlulah sempurna. Sebab setiap perubahan yang berlaku kepada diri kita sendiri sebenarnya mengubah benda2 lain, dan perubahan benda lain juga merubah kita. Jadi kalau kita cuma rekodkan perubahan diri kita aje, kita tak akan dapat balik ke belakang sebab data tak lengkap so takleh proses.

Tapi cuba bayangkan, even kalau kita hebat sangat boleh reverse every bit of all the processes, semua benda lain pun akan balik asal juga, kan?

Misalnya kalau sekarang kita start buat reversion untuk balik ke tahun 1980, maka everything around us termasuk diri kita sendiri shall be exactly the same as 1980 masa kita di tahun 1980 dulu. So, what's the point? Jika di tahun 1980 dulu kita berumur 10 tahun, tahun 2007 kita cipta mesin rentas masa dan balik ke tahun 1980 kita akan jadi budak 10 tahun tu jugak dan masa terus berjalan macam biasa. Tak mungkin kita boleh gunakan apa2 mesin rentas masa untuk balik ke 2007 sebab the first time masa kita jadi budak 10 tahun mesin rentas masa tu tak wujud. So kita pun membesar sebagaimana yang sebelumnya. By 2007 kita pun buat mesin rentas masa dan balik ke 1980 sekali lagi... Lepas tu kita jadi budak 10 tahun balik dan membesar sehingga kita mencipta mesin merentas masa pada tahun 2007... begitulah seterusnya dan lagi dan lagi... bila nak abis?

Macam tu jugak kalau kita nak merentas ke masa depan. Tak mungkin boleh sebab apa yang belum berlaku belum berlaku. Esok hanya wujud apabila kita hadir bersama-samanya. Kalau kita pandai2 cipta rekod "masa depan" itu dah bukan lagi masa depan tapi ia dah jadi "masa sekarang". Analoginya sekiranya kita berada di tahun 1980 kita tak boleh merentas masa ke tahun 2000 dan menemui KLCC di KL sebab pada tahun 1980 KLCC masih belum wujud. Mungkin anda kata kita buat lompatan kuantum ka apa. Yup, memang kita boleh lompat. Tapi cuba bayangkan kita lombat ke satu ketika yang belum wujud, kita nak mendarat kat mana? Saper boleh gerenti tahun 2010 mesti ada punya?

Beritahu aku kalau aku salah...

[ Last edited by paparock at 18-5-2007 01:16 AM ]

mziskandar · Post time 18-5-2007 03:37 AM

lompat kedepan boleh kut... nak lompat balik ke tempat asal (sekarang) atau masa silam je yg x boleh...

paparock · Post time 18-5-2007 07:12 AM

Kalau ikut logik atau law of nature kalau kita boleh lompat ke depan kita mesti boleh lompat ke belakang jugak. Kalau ke belakang tak boleh, ke depan pun tak akan boleh...

aku_EnSeM · Post time 19-5-2007 05:25 PM

Originally posted by paparock at 18-5-2007 12:28 AM
Aku berpendapat kita boleh bergerak semakin pantas tapi kita tak akan dapat keluar dari masa semasa kita. Maknanya perjalanan merentasi masa adalah mustahil. Kalau nak mempercepatkan masa perjala ...

good argument about the landing on where thing... it makes me sit back and start to think...

blastoff · Post time 19-5-2007 06:21 PM

Looking Back in Time

The Hubble Deep Field
Click on image for full size (100K JPEG)
Image Courtesy of NASA

When Astronomers probe the deepest regions of space they are actually looking back in time. This is simply because of the finite speed of light. Light moves at the speed of 300,000,000 meters/second (186,000 Miles/second). At short distances, like from satellites in orbit of Earth, the light travel time is only a fraction of a second. However, the Sun is so distant from Earth (150,000,000 Kilometers) that its light takes 8 minutes to reach us. So when you look at the sun in the sky (never look at it directly, you'll go blind) you see it as it was 8 minutes ago. As distances get larger so does this "look-back time." Our closest stellar neighbor, Alpha Centauri, is so far away that its light travels for 4.3 years before reaching us. When we look at the closest spiral galaxy to our own Milky Way, the Andromeda galaxy, we see it as it was 2 million years ago (when Homo Sapiens first began walking the Earth). The Hubble Space Telescope has taken a picture called the Hubble Deep Field (pictured here). When we gaze at those ancient galaxies we are seeing a distant part of the universe as it was billions of years ago (when Earth was still in its infancy).

http://www.windows.ucar.edu/tour/link=/the_universe/Lookback.html

[ Last edited by blastoff at 20-5-2007 12:54 AM ]

blastoff · Post time 19-5-2007 06:42 PM

So when we probe the deep space nothing we see actually take place at the exact moment of time we see it happen , we are actually looking at the past .

So for an alien who lives deep in space far far away from earth then if the alien can probe the earth from far away using any kind of sophisticated tool then the alien can see what our earth looks like in its infancy maybe

or the pharoahs' time , or the dinasours' era depending on the distance of the alien planet from earth ....

[ Last edited by blastoff at 19-5-2007 06:49 PM ]

blastoff · Post time 20-5-2007 12:50 AM

Cosmic Look-Back Time

NGC 6240

The finite speed of light means that we must always be out of date, no matter how hard we strive to keep up with the times. Thus, the seemingly simple question - what is happening right now on the Sun? - cannot be answered by an observer on Earth, because it takes light 8 minutes to reach Earth from the Sun. For distant galaxies, the light travel times are even longer, so our information about the galaxy NGC 6240, which is 400 million light years away, is 400 million years out of date! One consolation is that if astronomers on NGC 6240 are observing our Milky Way galaxy, they are likewise 400 million years behind the times - our times, that is. As Albert Einstein said, "The past, present and future are only illusions, even if stubborn ones."

Albert Einstein (Credit: Caltech)

The time in the past at which the light we now receive from a distant object was emitted is called the look-back time. When astronomers discuss events in distant objects, they take for granted that the actual event occurred earlier because of light travel time. It is similar to finding a series of photographs of a child in a 300 year-old time capsule. We could see how the child was developing 300 years ago, even though he/she would no longer be alive.

In the case of NGC 6240, the predicted merger of supermassive black holes has likely already occurred, perhaps 250 million years ago in NGC 6240 time. But we won't know about it for another 150 million years! See the following sample time line.

NGC 6240 sample time relative to Earth time:
450 million years earlier - Galaxies merged
400 million years earlier - Supermassive black holes are 3000 light years apart (Chandra Observation)
250 million years earlier - Black holes merged

Earth time:
50 million years ago: Galaxies merge
Now: Observe Supermassive black holes 3000 light years apart
150 million years from now: Black holes merge

http://chandra.harvard.edu/photo/cosmic_lookback.html

paparock · Post time 20-5-2007 01:28 AM

The article is basically talking about distance. This thread is talking about time travel...

wei_loon5063 · Post time 20-5-2007 01:32 AM

Originally posted by paparock at 20-5-2007 01:28 AM
The article is basically talking about distance. This thread is talking about time travel...

No.... he is on track...

Let me ask you.. what is time?

How do you see time?

what is light?

how is light relates to time?

paparock · Post time 20-5-2007 01:46 AM

Ermmm... but time travel is about getting somewhere in the past or in future in real time. Light traveling from a distance star is about something moving from point A to point B..

[ Last edited by paparock at 20-5-2007 01:47 AM ]

wei_loon5063 · Post time 20-5-2007 01:51 AM

You are lost....
You need to understand what time, space and space-time is first.
then understand light.then learn relativity.then learn what is past, what is now, what is future.

[quote]
In special relativity, a light cone is the pattern describing the temporal evolution of a flash of light in Minkowski spacetime. This can be visualized in 3-space if the two horizontal axis are chosen to be spatial dimensions, while the vertical axis is time.
The light cone is constructed as follows. Taking as event p a flash of light (light pulse) at time t0, all events that can be reached by this pulse from p form the future light cone of p, whilst those events that can send a light pulse to p form the past light cone of p.
Given an event E, the light cone classifies all events in spacetime into 5 distinct categories:

Events on the future light cone of E.

Events on the past light cone of E.

Events inside the future light cone of E are those which are affected by a material particle emitted at E.

Events inside the past light cone of E are those which can emit a material particle and affect what is happening at E.

All other events are in the (absolute) elsewhere of E and are those that will never affect and can never be affected by E.

If space is measured in light-seconds and time is measured in seconds, the cone will have a slope of 45

paparock · Post time 20-5-2007 02:21 AM

Given an event O on my worldline, find my plane of simultaneity. Set my wristwatch to read 12:00 at event O.
Suppose I sent out a light-pulse at 11:59, suitably aimed so that the pulse will reach event X.
And suppose I receive an echo from event X at 12:01. What could I say about event X?
Well, it took two minutes to get there to event X and back. So, it must have taken light one minute (that is, half the roundtrip-time) to get to X.
Well, if it was there one minute after I sent the light-pulse out, my watch must have read 12:00 when the pulse reached X. Therefore, I say that "event X is simultaneous with event O."
And, since the light-pulse, travelling at the speed of light, took one minute to get to X, then I say that "event X is a length 1 light-minute away from event O." (This length makes sense to me because I measured it between two simultaneous events.)
Suppose I had sent out another light pulse earlier at 11:58 toward event Y and received its echo at 12:02. I would say "event Y is also simultaneous with event O, and it is 2 light-minutes away from me." ...and, so forth. I would say that all such events would be simultaneous with event O. Realize, however, that MY determination of "which events were simultaneous with event O" will generally differ from that of another observer (even if event O is also on his worldline).

I need time to counter this one. A bit tricky for me... hehehe

[ Last edited by paparock at 20-5-2007 02:51 AM ]