
Number Theory Number Theory Math Forum 
 LinkBack  Thread Tools  Display Modes 
September 10th, 2017, 09:14 AM  #1 
Member Joined: May 2013 Posts: 34 Thanks: 1  are the real numbers truly more infinite than the rationals
In Hilbert's hotel, he has a infinite number of guests, the whole numbers staying in an infinite number of rooms. An infinitely long bus comes along with infinite passengers, the rationals. To fit them in, he makes each guest in his hotel move to the room 2*room number. then he has an infinite number of buses containing an infinite number of people in each bus arrive. the polynomial numbers. (Bus 1 could be square root of all the rational numbers, bus 2 the cube root, bus 3, the fourth root, and so on.) To fit them in, he puts all the people in bus 1 in 2^bus seat number, all the people in bus 2 in 3^bus seat number and so on with all the primes. now the only thing left would be the nonpolynomial numbers, or otherwise known as the transcendental numbers. Those also come in on an infinite number of buses with an infinite number of people. (pi, e, and so on.) to fit those in we put them in composite powers. bus 1 (2*3)^bus seat number, bus 2 (2*5)^bus seat number, bus 3 (2*7)^bus seat number, bus 4 (3*5)^bus seat number and so on. now all the numbers in the real set have been accounted for, haven't they? Last edited by skipjack; September 10th, 2017 at 09:34 AM. 
September 10th, 2017, 09:30 AM  #2 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,237 Thanks: 2412 Math Focus: Mainly analysis and algebra 
You are assuming that each new set is countable before you try to accommodate it in the hotel. The transcendental numbers are not countable.

September 10th, 2017, 10:50 AM  #3 
Senior Member Joined: Jun 2015 From: England Posts: 768 Thanks: 223 
The study of this subject starts with Cantor's Continuum Hypothesis. (Which might be considered a strange name considering what it actually says) Continuum Hypothesis  from Wolfram MathWorld 
September 10th, 2017, 11:08 AM  #4  
Senior Member Joined: Aug 2012 Posts: 1,783 Thanks: 482  Quote:
How would CH have any relevance to the OP's question? Last edited by Maschke; September 10th, 2017 at 11:17 AM.  
September 10th, 2017, 12:00 PM  #5 
Senior Member Joined: Jun 2015 From: England Posts: 768 Thanks: 223 
I said it's where this started. I didn't say its the be all and end all of the subject. And I'm happy for Phillip to decide for himself whether it is of interest or not. Last edited by studiot; September 10th, 2017 at 12:04 PM. 
September 10th, 2017, 01:10 PM  #6  
Senior Member Joined: Aug 2012 Posts: 1,783 Thanks: 482  But that's false, historically and factually. Historically, Cantor's first proof of the uncountability of the reals was published in 1874; and he proposed CH in 1878. And factually, the reals are uncountable regardless of the status of CH or any assumption you could make about its truth value. https://en.wikipedia.org/wiki/Georg_...theory_article https://en.wikipedia.org/wiki/Continuum_hypothesis I'm just wondering why you brought it up at all, since it's totally unrelated to the OP's question of whether the reals are indeed uncountable. Quote:
If you misspoke yourself I don't mean to poke you. If you're just a little confused, I'd be glad to explain it. But why double down on an error? The reals are uncountable. Cantor gave three proofs. CH is the statement that there's no uncountable cardinal strictly between the naturals and the reals. Whether we take it as true or false (which we are free to do since it's independent of the other axioms of set theory) the reals are still uncountable. Last edited by Maschke; September 10th, 2017 at 01:22 PM.  
September 10th, 2017, 02:09 PM  #7  
Senior Member Joined: Jun 2015 From: England Posts: 768 Thanks: 223  Quote:
Equally the issue of whether there is an uncountable cardinal between the naturals and the reals only makes sense if the reals are uncountable in some way to make their cardinality greater than that of the naturals, just as Phillip asked. On the same day that I offered Phillip this prompt towards his investigation, I suggested the phrase 'Thermal Resistance in relation to electrical theory' to someone else on another site. Within a few hours I had a reply saying that was just the right phrase for the questioner to research and he had thus been able to complete the solution of his problem. In my experience questioners don't often ask their questions in the nice tight phraseology that textbook and exam questions are (hopefully) written and rarely say exactly what they mean.  
September 10th, 2017, 02:29 PM  #8  
Senior Member Joined: Aug 2012 Posts: 1,783 Thanks: 482  Quote:
Last edited by Maschke; September 10th, 2017 at 02:31 PM.  

Tags 
infinite, numbers, rationals, real 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Real Numbers and Natural Numbers  zylo  Topology  14  May 10th, 2017 01:57 AM 
Dimensions, and numbers beyond real numbers  Elektron  Math  4  May 7th, 2017 11:47 AM 
infinite numbers  shaharhada  Number Theory  4  January 21st, 2017 04:35 AM 
Infinite set of numbers  kustrle  Number Theory  4  October 18th, 2015 12:29 PM 
Probability of finite padic numbers within rationals  elim  Probability and Statistics  0  July 21st, 2010 02:03 PM 